MULTI-PORT FUEL INJECTION …billhughes.com/temp/95yjFuel.pdf† Engine coolant temperature sensor † Crankshaft position sensor † Ignition circuit sense (ignition switch in run

MULTI-PORT FUEL INJECTION (MFI)—COMPONENT DESCRIPTION/SYSTEMOPERATION

INDEX

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Air Cleaner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Air Conditioning (A/C) Clutch Relay—PCM Output . 26Air Conditioning (A/C) Controls—PCM Input . . . . . . 21Auto Shutdown (ASD) Relay—PCM Output . . . . . . 26Automatic Shutdown (ASD) Sense—PCM Input . . . 21Battery Voltage—PCM Input . . . . . . . . . . . . . . . . . 21Brake Switch—PCM Input . . . . . . . . . . . . . . . . . . . 22Camshaft Position Sensor—PCM Input . . . . . . . . . 22Crankshaft Position Sensor—PCM Input . . . . . . . . 22Data Link Connector—PCM Input . . . . . . . . . . . . . 22Data Link Connector—PCM Output . . . . . . . . . . . . 27EMR Lamp—PCM Output . . . . . . . . . . . . . . . . . . . 27Engine Coolant Temperature Sensor—PCM Input . 23Extended Idle Switch—PCM Input . . . . . . . . . . . . . 23Fuel Injectors—PCM Output . . . . . . . . . . . . . . . . . 27Fuel Pressure Regulator . . . . . . . . . . . . . . . . . . . . 33Fuel Pump Relay—PCM Output . . . . . . . . . . . . . . 27Fuel Rail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33General Information . . . . . . . . . . . . . . . . . . . . . . . 19Generator Field—PCM Output . . . . . . . . . . . . . . . . 27Generator Lamp—PCM Output . . . . . . . . . . . . . . . 27Idle Air Control (IAC) Motor—PCM Output . . . . . . . 27Ignition Circuit Sense—PCM Input . . . . . . . . . . . . . 23Ignition Coil—PCM Output . . . . . . . . . . . . . . . . . . . 28

Intake Manifold Air Temperature Sensor—PCM Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Malfunction Indicator Lamp—PCM Output . . . . . . . 28Manifold Absolute Pressure (MAP) Sensor—PCM

Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Open Loop/Closed Loop Modes of Operation . . . . . 30Oxygen (O2S) Sensor—PCM Input . . . . . . . . . . . . 24Park/Neutral Switch—PCM Input . . . . . . . . . . . . . . 24Power Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Power Steering Pressure Switch—PCM Input . . . . 24Powertrain Control Module (PCM) . . . . . . . . . . . . . 20Radiator Fan Relay—PCM Output . . . . . . . . . . . . . 28SCI Receive—PCM Input . . . . . . . . . . . . . . . . . . . 24SCI Transmit—PCM Output . . . . . . . . . . . . . . . . . . 29Sensor Return—PCM Input . . . . . . . . . . . . . . . . . . 25Shift Indicator—PCM Output . . . . . . . . . . . . . . . . . 29Speed Control—PCM Input . . . . . . . . . . . . . . . . . . 25Speed Control—PCM Output . . . . . . . . . . . . . . . . . 29Tachometer—PCM Output . . . . . . . . . . . . . . . . . . . 29Throttle Body . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Throttle Position Sensor (TPS)—PCM Input . . . . . . 25Torque Converter Clutch Relay—PCM Output . . . . 29Vehicle Speed Sensor—PCM Input . . . . . . . . . . . . 25

GENERAL INFORMATIONAll 2.5L 4-cylinder and 4.0L 6-cylinder engines are

equipped with sequential Multi-Port Fuel Injection(MFI). The MFI system provides precise air/fuel ra-tios for all driving conditions.

The Powertrain Control Module (PCM) operatesthe fuel system. The PCM was formerly referred toas the SBEC or engine controller. The PCM is a pre-programmed, dual microprocessor digital computer. Itregulates ignition timing, air-fuel ratio, emission con-trol devices, charging system, speed control, air con-ditioning compressor clutch engagement and idlespeed. The PCM can adapt its programming to meetchanging operating conditions.

Powertrain Control Module (PCM) Inputs rep-resent the instantaneous engine operating conditions.Air-fuel mixture and ignition timing calibrations forvarious driving and atmospheric conditions are pre-programmed into the PCM. The PCM monitors andanalyzes various inputs. It then computes engine fueland ignition timing requirements based on these in-puts. Fuel delivery control and ignition timing willthen be adjusted accordingly.

Other inputs to the PCM are provided by the brakelight switch, air conditioning select switch and thespeed control switches. All inputs to the PCM areconverted into signals.

Electrically operated fuel injectors spray fuel in

precise metered amounts into the intake port directlyabove the intake valve. The injectors are fired in aspecific sequence by the PCM. The PCM maintainsan air/fuel ratio of 14.7 to 1 by constantly adjustinginjector pulse width. Injector pulse width is thelength of time that the injector opens and sprays fuelinto the chamber. The PCM adjusts injector pulsewidth by opening and closing the ground path to theinjector.

Manifold absolute pressure (air density) and enginerpm (speed) are the primary inputs that determinefuel injector pulse width. The PCM also monitorsother inputs when adjusting air-fuel ratio.

Inputs That Effect Fuel Injector Pulse Width:• Exhaust gas oxygen content• Engine coolant temperature• Manifold absolute pressure (MAP)• Engine speed• Throttle position• Battery voltage• Air conditioning selection• Transmission gear selection (automatic transmis-sions only)• Speed control

The powertrain control module (PCM) adjusts igni-tion timing by controlling ignition coil operation. Theignition coil receives battery voltage when the igni-tion key is in the run or starter position. The PCM

J FUEL SYSTEM COMPONENT DESCRIPTION/SYSTEM OPERATION 14 - 19

provides a ground for the ignition coil. The coil dis-charges when the PCM supplies a ground. By switch-ing the ground path on and off, the PCM regulatesignition timing.

The sensors and switches that provide inputs tothe powertrain control module (PCM) comprise theEngine Control System. It is also comprised of thePCM Outputs (engine control devices that the are op-erated by the PCM).

SYSTEM DIAGNOSISThe powertrain control module (PCM) tests many

of its own input and output circuits. If a DiagnosticTrouble Code (DTC) is found in a major system, thisinformation is stored in the PCM memory. Refer toOn-Board Diagnostics in the MFI System—GeneralDiagnosis section of this group for DTC information.

POWERTRAIN CONTROL MODULE (PCM)The PCM operates the fuel system. The PCM was

formerly referred to as the SBEC or engine control-ler. The PCM is a pre-programmed, dual microproces-sor digital computer. It regulates ignition timing, air-fuel ratio, emission control devices, charging system,speed control, air conditioning compressor clutch en-gagement and idle speed. The PCM can adapt itsprogramming to meet changing operating conditions.

On XJ models, the PCM is located in the enginecompartment next to the air cleaner (Fig. 1). On YJmodels, the PCM is located in the engine compart-ment behind the windshield washer fluid reservoir(Fig. 2).

The PCM receives input signals from variousswitches and sensors. Based on these inputs, thePCM regulates various engine and vehicle operationsthrough different system components. These compo-nents are referred to as PCM Outputs. The sensorsand switches that provide inputs to the PCM are con-sidered PCM Inputs.

The PCM adjusts ignition timing based upon in-puts it receives from sensors that react to: enginerpm, manifold absolute pressure, coolant tempera-ture, throttle position, transmission gear selection(automatic transmission), vehicle speed and thebrake switch.

The PCM adjusts idle speed based on inputs it re-ceives from sensors that react to: throttle position,vehicle speed, transmission gear selection, coolanttemperature and from inputs it receives from the airconditioning clutch switch and brake switch.

Based on inputs that it receives, the PCM adjustsignition coil dwell. The PCM also adjusts the gener-ator charge rate through control of the generatorfield and provides speed control operation.

Powertrain Control Module (PCM) Inputs:• Generator output• A/C request (if equipped with factory A/C)• A/C select (if equipped with factory A/C)• Auto shutdown (ASD) sense• Intake manifold air temperature sensor• Battery voltage• Brake switch• Engine coolant temperature sensor• Crankshaft position sensor• Ignition circuit sense (ignition switch in run posi-tion)• Manifold absolute pressure sensor• Overdrive/override switch• Oxygen sensor• Park/neutral switch (auto. trans. only)• SCI receive (DRB scan tool connection)• Speed control resume switch• Speed control set switch• Speed control on/off switch• Camshaft position sensor signal• Throttle position sensor• Vehicle speed sensor• Sensor return• Power ground

Fig. 1 PCM Location—XJ Models

Fig. 2 PCM Location—YJ Models

14 - 20 FUEL SYSTEM COMPONENT DESCRIPTION/SYSTEM OPERATION J

• Signal groundPowertrain Control Module (PCM) Outputs:

• A/C clutch relay• Idle air control (IAC) motor• Auto shutdown (ASD) relay• Generator field• Malfunction indicator lamp (Check Engine Lamp)• Fuel injectors• Fuel pump relay• Ignition coil• SCI transmit (DRB scan tool connection)• Shift indicator lamp (manual transmission only)• Speed control vacuum solenoid• Speed control vent solenoid• Tachometer (on instrument panel, if equipped)• Torque converter clutch relay (3-speed auto. trans.only)

The PCM contains a voltage convertor. This con-verts battery voltage to a regulated 8.0 volts. It isused to power the crankshaft position sensor, cam-shaft position sensor and vehicle speed sensor. ThePCM also provides a five (5) volt supply for the Man-ifold Absolute Pressure (MAP) sensor and ThrottlePosition Sensor (TPS).

AIR CONDITIONING (A/C) CONTROLS—PCM INPUTThe A/C control system information applies to fac-

tory installed air conditioning units only.A/C SELECT SIGNAL: When the A/C switch is in

the ON position and the A/C low-pressure switch isclosed, an input signal is sent to the powertrain con-trol module (PCM). The signal informs the PCM thatthe A/C has been selected. The PCM adjusts idlespeed to a pre-programmed rpm through the idle aircontrol (IAC) motor to compensate for increased en-gine load.

A/C REQUEST SIGNAL: Once A/C has been se-lected, the PCM receives the A/C request signal fromthe evaporator switch. The input indicates that theevaporator temperature is in the proper range forA/C application. The PCM uses this input to cycle theA/C compressor clutch (through the A/C relay). It willalso determine the correct engine idle speed throughthe IAC motor position.

If the A/C low-pressure switch opens (indicating alow refrigerant level), the PCM will not receive anA/C select signal. The PCM will then remove theground from the A/C relay. This will deactivate theA/C compressor clutch.

If the evaporator switch opens, (indicating thatevaporator is not in proper temperature range), thePCM will not receive the A/C request signal. ThePCM will then remove the ground from the A/C relay,deactivating the A/C compressor clutch.

AUTOMATIC SHUTDOWN (ASD) SENSE—PCMINPUT

A 12 volt signal at this input indicates to the PCMthat the ASD has been activated. The ASD relay islocated in the power distribution center (PDC) in theengine compartment (Figs. 3 or 4). It is used to con-nect the ignition coil, generator field winding andfuel injectors to 12 volt + power supply. Also refer toAutomatic Shutdown Relay—PCM Output.

This input is used only to sense that the ASD relayis energized. If the PCM does not see 12 volts at thisinput when the ASD should be activated, it will set aDiagnostic Trouble Code (DTC).

BATTERY VOLTAGE—PCM INPUTThe battery voltage input provides power to the

powertrain control module (PCM). It also informs thePCM what voltage level is supplied to the ignitioncoil and fuel injectors.

If battery voltage is low, the PCM will increase in-jector pulse width (period of time that the injector is

Fig. 3 Power Distribution Center—YJ Models

Fig. 4 Power Distribution Center—XJ Models


energized). This is done to compensate for the re-duced flow through injector caused by the loweredvoltage.

BRAKE SWITCH—PCM INPUTWhen the brake light switch is activated, the pow-

ertrain control module (PCM) receives an input indi-cating that the brakes are being applied. Afterreceiving this input, the PCM maintains idle speed toa scheduled rpm through control of the idle air con-trol (IAC) motor. The brake switch input is also usedto operate the speed control system.

CAMSHAFT POSITION SENSOR—PCM INPUTA sync signal is provided by the camshaft position

sensor located in the distributor (Fig. 5). The syncsignal from this sensor works in conjunction with thecrankshaft position sensor to provide the powertraincontrol module (PCM) with inputs. This is done to es-tablish and maintain correct injector firing order.

Refer to Camshaft Position Sensor in Group 8D, Ig-nition System for more information.

DATA LINK CONNECTOR—PCM INPUTThe data link connector (diagnostic scan tool con-

nector) links the DRB scan tool with the powertraincontrol module (PCM). The data link connector is lo-cated in the engine compartment (Figs. 6 or 7). Foroperation of the DRB scan tool, refer to the appropri-ate Powertrain Diagnostic Procedures service man-ual.

The data link connector uses two different pins onthe PCM. One is for Data Link Transmit and theother is for Data Link Receive.

INTAKE MANIFOLD AIR TEMPERATURE SENSOR—PCM INPUT

The intake manifold air temperature sensor is in-stalled in the intake manifold with the sensor ele-ment extending into the air stream (Figs. 8 or 9). The

sensor provides an input voltage to the powertraincontrol module (PCM) indicating intake manifold airtemperature. The input is used along with inputsfrom other sensors to determine injector pulse width.As the temperature of the air-fuel stream in themanifold varies, the sensor resistance changes. Thisresults in a different input voltage to the PCM.

CRANKSHAFT POSITION SENSOR—PCM INPUTThis sensor is a Hall Effect device that detects

notches in the flywheel (manual transmission), orflexplate (automatic transmission).

This sensor is used to indicate to the powertraincontrol module (PCM) that a spark and or fuel injec-tion event is to be required. The output from thissensor, in conjunction with the camshaft position sen-sor signal, is used to differentiate between fuel injec-tion and spark events. It is also used to synchronizethe fuel injectors with their respective cylinders.

Refer to Group 8D, Ignition System for more crank-shaft position sensor information.

Fig. 5 Camshaft Position Sensor

Fig. 6 Data Link Connector—YJ Models—Typical

Fig. 7 Data Link Connector—XJ Models—Typical


The engine will not operate if the PCM does not re-ceive a crankshaft position sensor input.

ENGINE COOLANT TEMPERATURE SENSOR—PCMINPUT

The engine coolant temperature sensor is installedin the thermostat housing (Fig. 10) and protrudesinto the water jacket. The sensor provides an inputvoltage to the powertrain control module (PCM) re-lating coolant temperature. The PCM uses this inputalong with inputs from other sensors to determine in-jector pulse width and ignition timing. As coolanttemperature varies, the coolant temperature sensor’sresistance changes. The change in resistance resultsin a different input voltage to the PCM.

When the engine is cold, the PCM will operate inOpen Loop cycle. It will demand slightly richer air-fuel mixtures and higher idle speeds. This is doneuntil normal operating temperatures are reached.

Refer to Open Loop/Closed Loop Modes of Opera-tion in this section of the group for more information.

EXTENDED IDLE SWITCH—PCM INPUT

OPTIONAL POLICE PACKAGE ONLYThe extended idle switch is used to raise the en-

gine idle speed to approximately 1000 rpm. This iswhen the shifter is in either the Park or Neutral po-sition. A rocker-type 2-wire switch (extended idleswitch) is mounted to the instrument panel. Thisswitch will supply a ground circuit to the powertraincontrol module (PCM). The switch is availableonly with 4.0L engine when supplied with theoptional police package.

For testing and diagnosis of this switch and its cir-cuit, refer to the MFI System—General Diagnosissection of this group.

IGNITION CIRCUIT SENSE—PCM INPUTThe ignition circuit sense input tells the powertrain

control module (PCM) the ignition switch has ener-gized the ignition circuit. Refer to the wiring dia-grams for circuit information.

MANIFOLD ABSOLUTE PRESSURE (MAP)SENSOR—PCM INPUT

The MAP sensor reacts to absolute pressure in theintake manifold. It provides an input voltage to thepowertrain control module (PCM). As engine loadchanges, manifold pressure varies. The change inmanifold pressure causes MAP sensor voltage tochange. The change in MAP sensor voltage results ina different input voltage to the PCM. The input volt-age level supplies the PCM with information aboutambient barometric pressure during engine start-up(cranking) and engine load while the engine is run-ning. The PCM uses this input along with inputsfrom other sensors to adjust air-fuel mixture.

Fig. 8 Sensor Location—4.0L Engine


Fig. 10 Engine Coolant Temperature Sensor—Typical


The MAP sensor is mounted on the dash panel.The sensor is connected to the throttle body with avacuum hose and to the PCM electrically.

OXYGEN (O2S) SENSOR—PCM INPUTThe O2S sensor is located in the exhaust down pipe

(Fig. 11). It provides an input voltage to the power-train control module (PCM) relating the oxygen con-tent of the exhaust gas. The PCM uses thisinformation to fine tune the air-fuel ratio by adjust-ing injector pulse width.

The O2S sensor produces voltages from 0 to 1 volt.This voltage will depend upon the oxygen content ofthe exhaust gas in the exhaust manifold. When alarge amount of oxygen is present (caused by a leanair-fuel mixture), the sensor produces a low voltage.When there is a lesser amount present (rich air-fuelmixture) it produces a higher voltage. By monitoringthe oxygen content and converting it to electricalvoltage, the sensor acts as a rich-lean switch.

The oxygen sensor is equipped with a heating ele-ment that keeps the sensor at proper operating tem-perature during all operating modes. Maintainingcorrect sensor temperature at all times allows thesystem to enter into closed loop operation sooner.

In Closed Loop operation, the powertrain controlmodule (PCM) monitors the O2S sensor input (alongwith other inputs). It then adjusts the injector pulsewidth accordingly. During Open Loop operation, thePCM ignores the O2S sensor input and adjusts injec-tor pulse width to a preprogrammed value (based onother sensor inputs).

PARK/NEUTRAL SWITCH—PCM INPUTThe park/neutral switch is located on the transmis-

sion housing and provides an input to the powertraincontrol module (PCM). This will indicate that the au-tomatic transmission is in Park, Neutral or a drivegear selection. This input is used to determine idlespeed (varying with gear selection), fuel injectorpulse width, ignition timing advance and vehicle

speed control operation. Refer to Group 21, Transmis-sions, for testing, replacement and adjustment infor-mation.

POWER GROUNDThe power ground is used to control ground circuits

for the following powertrain control module (PCM)loads:• Generator Field Winding• 8 volt (PCM) power supply• Fuel Injectors• Ignition Coil

POWER STEERING PRESSURE SWITCH—PCMINPUT

A pressure sensing switch is included in the powersteering system (mounted on the high-pressure line).This switch will be on vehicles equipped with a 2.5Lengine and power steering. The switch (figure 12, YJmodels or figure 13, XJ models) provides an input tothe PCM. This input is provided during periods ofhigh pump load and low engine rpm; such as duringparking maneuvers. The PCM will then increase theidle speed through the idle air control (IAC) motor.This is done to prevent the engine from stalling un-der the increased load.

When steering pump pressure exceeds 1896 kPa 6172 kPa (275 6 25 psi) the PCM will increase the en-gine idle speed. This will prevent the engine fromstalling.

SCI RECEIVE—PCM INPUTSCI Receive is the serial data communication re-

ceive circuit for the DRB scan tool. The powertraincontrol module (PCM) receives data from the DRBthrough the SCI Receive circuit.

Fig. 11 Heated Oxygen Sensor Location—TypicalFig. 12 Power Steering Pump Pressure Switch—YJ

Models


SPEED CONTROL—PCM INPUTThe speed control system provides three separate

inputs to the powertrain control module (PCM); On/Off, Set and Resume. The On/Off input informs thePCM that the speed control system has been acti-vated. The Set input informs the PCM that a fixedvehicle speed has been selected. The Resume inputindicates to the PCM that the previous fixed speed isrequested.

The speed control operating range is from 50 km/hto 142 km/h (35 to 85 mph). Inputs that effect speedcontrol operation are:• Brake switch position• Park/neutral switch• Vehicle speed sensor• Throttle position sensor

Refer to Group 8H for further speed control infor-mation.

SENSOR RETURN—PCM INPUTSensor Return provides a low noise ground refer-

ence for all system sensors.

THROTTLE POSITION SENSOR (TPS)—PCM INPUTThe throttle position sensor (TPS) is mounted on

the throttle body (Figs. 14 or 15). The TPS is a vari-able resistor that provides the powertrain controlmodule (PCM) with an input signal (voltage) thatrepresents throttle blade position. The sensor is con-nected to the throttle blade shaft. As the position ofthe throttle blade changes, the resistance of the TPSchanges.

The PCM supplies approximately 5 volts to theTPS. The TPS output voltage (input signal to thePCM) represents the throttle blade position. ThePCM receives an input signal voltage from the TPS.This will vary in an approximate range of from 1 voltat minimum throttle opening (idle), to 4 volts at wideopen throttle. Along with inputs from other sensors,

the PCM uses the TPS input to determine currentengine operating conditions. In response to engineoperating conditions, the PCM will adjust fuel injec-tor pulse width and ignition timing.

VEHICLE SPEED SENSOR—PCM INPUTThe vehicle speed sensor (Fig. 16) is located in the

extension housing of the transmission (2 wheel drive)or on the transfer case extension housing (4 wheeldrive). The sensor input is used by the powertraincontrol module (PCM) to determine vehicle speed anddistance traveled.

The speed sensor generates 8 pulses per sensorrevolution. These signals, in conjunction with aclosed throttle signal from the throttle position sen-sor, indicate a closed throttle deceleration to thePCM. When the vehicle is stopped at idle, a closedthrottle signal is received by the PCM (but a speedsensor signal is not received).

Under deceleration conditions, the PCM adjusts theidle air control (IAC) motor to maintain a desiredMAP value. Under idle conditions, the PCM adjuststhe IAC motor to maintain a desired engine speed.

Fig. 13 Power Steering Pump Pressure Switch—XJModels

Fig. 14 Throttle Position Sensor—2.5L Engine

Fig. 15 Throttle Position Sensor—4.0L Engine


AIR CONDITIONING (A/C) CLUTCH RELAY—PCMOUTPUT

The powertrain control module (PCM) activates theA/C compressor through the A/C clutch relay. ThePCM regulates A/C compressor operation by switch-ing the ground circuit for the A/C clutch relay on andoff. The relay is located in the power distributioncenter (PDC) (Figs. 17 or 18). For the location of therelay within the PDC, refer to label on PDC cover.

When the PCM receives a request for A/C from A/Cevaporator switch, it will adjust idle air control (IAC)motor position. This is done to increase idle speed.The PCM will then activate the A/C clutch throughthe A/C clutch relay. The PCM adjusts idle air control(IAC) stepper motor position to compensate for in-creased engine load from the A/C compressor.

By switching the ground path for the relay on andoff, the PCM is able to cycle the A/C compressorclutch. This is based on changes in engine operatingconditions. If, during A/C operation, the PCM senseslow idle speeds or a wide open throttle condition, itwill de-energize the relay. This prevents A/C clutchengagement. The relay will remain de-energized untilthe idle speed increases or the wide open throttlecondition exceeds 15 seconds or no longer exists. ThePCM will also de-energize the relay if coolant tem-perature exceeds 125°C (257°F).

AUTO SHUTDOWN (ASD) RELAY—PCM OUTPUTThe ASD relay is located in the power distribution

center (PDC) (Figs. 17 or 18). For the location of thisrelay within the PDC, refer to label on PDC cover.

The ASD supplies battery voltage to the fuel injec-tors, ignition coil and generator field winding. Theground circuit for the coil in the ASD relay is con-trolled by the powertrain control module (PCM). ThePCM operates the relay by switching the ground cir-cuit on and off.

The fuel pump relay is controlled by the PCMthrough same circuit that the ASD relay is con-trolled.

The powertrain control module (PCM) energizesthe fuel pump through the fuel pump relay. (ThePCM was formerly referred to as the SBEC or enginecontroller). Battery voltage is applied to the relayfrom the ignition switch. The relay is energized whena ground is provided by the PCM. The relay is lo-cated in the power distribution center (PDC) (Figs.17 or 18). For the location of fuel pump relay withinPDC, refer to label on PDC cover.

For the 1995 model year, the ballast resistor andballast resistor bypass relay are no longer used tocontrol the fuel pump circuit.

Fig. 16 Vehicle Speed Sensor—Typical

Fig. 17 PDC—YJ Models

Fig. 18 PDC—XJ Models


DATA LINK CONNECTOR—PCM OUTPUTRefer to the previous paragraphs on Data Link

Connector—PCM Input for information.

EMR LAMP—PCM OUTPUTThe EMR (SRI) lamp is not used for the 1995

model year.

FUEL PUMP RELAY—PCM OUTPUTThe PCM energizes the fuel pump and the oxygen

sensor (O2S) heating element through the fuel pumprelay. Battery voltage is applied to the relay from theignition switch. The relay is energized when aground is provided by the PCM. Refer to AutomaticShutdown Relay for additional information.

FUEL INJECTORS—PCM OUTPUTSix individual fuel injectors are used with the 4.0L

6-cylinder engine. Four individual fuel injectors areused with the 2.5L 4-cylinder engine. The injectorsare attached to the fuel rail (Fig. 19).

The nozzle ends of the injectors are positioned intoopenings in the intake manifold just above the intakevalve ports of the cylinder head. The engine wiringharness connector for each fuel injector is equippedwith an attached numerical tag (INJ 1, INJ 2 etc.).This is used to identify each fuel injector.

The injectors are energized individually in a se-quential order by the powertrain control module(PCM). The PCM will adjust injector pulse width byswitching the ground path to each individual injectoron and off. Injector pulse width is the period of timethat the injector is energized. The PCM will adjustinjector pulse width based on various inputs it re-ceives.

During start up, battery voltage is supplied to theinjectors through the ASD relay. When the engine isoperating, voltage is supplied by the charging sys-tem. The PCM determines injector pulse width basedon various inputs.

GENERATOR FIELD—PCM OUTPUTThe powertrain control module (PCM) regulates the

charging system voltage within a range of 12.9 to15.0 volts. Refer to Group 8A for charging system in-formation.

GENERATOR LAMP—PCM OUTPUT

IF EQUIPPEDIf the powertrain control module (PCM) senses a

low charging condition in the charging system, it willilluminate the generator lamp on the instrumentpanel. For example, during low idle with all accesso-ries turned on, the lamp may momentarily go on.Once the PCM corrects idle speed to a higher rpm,the lamp will go out. Refer to Group 8A, Battery/Starting/Charging Systems for charging system infor-mation.

IDLE AIR CONTROL (IAC) MOTOR—PCM OUTPUTThe IAC motor is mounted on the throttle body

(Figs. 20 or 21) and is controlled by the powertraincontrol module (PCM).

Fig. 19 Fuel Injectors—Typical

Fig. 20 IAC Motor—4.0L Engine

Fig. 21 IAC Motor—2.5L Engine


The throttle body has an air control passage thatprovides air for the engine at idle (the throttle plateis closed). The IAC motor pintle protrudes into theair control passage and regulates air flow through it.Based on various sensor inputs, the powertrain con-trol module (PCM) adjusts engine idle speed by mov-ing the IAC motor pintle in and out of the air controlpassage. The IAC motor is positioned when the igni-tion key is turned to the On position.

A (factory adjusted) set screw is used to mechani-cally limit the position of the throttle body throttleplate. Never attempt to adjust the engine idlespeed using this screw. All idle speed functions arecontrolled by the PCM.

IGNITION COIL—PCM OUTPUTSystem voltage is supplied to the ignition coil pos-

itive terminal. The powertrain control module (PCM)operates the ignition coil. Base (initial) ignitiontiming is not adjustable. The PCM adjusts ignitiontiming to meet changing engine operating conditions.

The ignition coil is located near the distributor(Fig. 22).

Refer to Group 8D, Ignition System for additionalinformation.

MALFUNCTION INDICATOR LAMP—PCM OUTPUTThe malfunction indicator lamp illuminates each

time the ignition key is turned on. It will stay on forapproximately three seconds as a bulb test. The lampis displayed on the instrument panel as the CHECKENGINE lamp (Figs. 23 or 24).

If the powertrain control module (PCM) receives anincorrect signal, or no signal from certain sensors oremission related systems, the lamp is turned on. Thisis a warning that the PCM has recorded a system orsensor malfunction. In some cases, when a problem isdeclared, the PCM will go into a limp-in mode. Thisis an attempt to keep the system operating. It signalsan immediate need for service.

The lamp can also be used to display a DiagnosticTrouble Code (DTC). Cycle the ignition switch On-Off-On-Off-On within three seconds and any codesstored in the PCM memory will be displayed. This isdone in a series of flashes representing digits. Referto On-Board Diagnostics in the General Diagnosissection of this group for more information.

RADIATOR FAN RELAY—PCM OUTPUT

XJ MODELS ONLYThe electric radiator cooling fan used in XJ models

(equipped with 4.0L engine, heavy duty coolingand/or air conditioning) is controlled by the power-train control module (PCM) through radiator fan re-lay. The relay is energized when coolant temperatureis above 103°C (217°F). It will then de-energize when

Fig. 22 Ignition Coil—Typical

Fig. 23 Check Engine Lamp—XJ Models—Typical

Fig. 24 Check Engine Lamp—YJ Models—Typical


coolant temperature drops to 98°C (208°F). Refer toGroup 7, Cooling Systems for more information.

The relay is located in the power distribution cen-ter (PDC) (Fig. 25).

The electric radiator cooling fan is not used on YJmodels.

SCI TRANSMIT—PCM OUTPUTSCI Transmit is the serial data communication

transmit circuit for the DRB scan tool. The power-train control module (PCM) transmits data to theDRB through the SCI Transmit circuit.

SHIFT INDICATOR—PCM OUTPUTVehicles equipped with manual transmissions have

an Up-Shift indicator lamp. The lamp is controlled bythe powertrain control module (PCM). The lamp illu-minates on the instrument panel to indicate whenthe driver should shift to the next highest gear forbest fuel economy. The PCM will turn the lamp OFFafter 3 to 5 seconds if the shift of gears is not per-formed. The up-shift lamp will remain off until vehi-cle stops accelerating and is brought back to range ofup-shift lamp operation. This will also happen if ve-hicle is shifted into fifth gear.

The indicator lamp is normally illuminated whenthe ignition switch is turned on and it is turned offwhen the engine is started up. With the engine run-ning, the lamp is turned on/off depending upon en-gine speed and load.

SPEED CONTROL—PCM OUTPUTSpeed control operation is regulated by the power-

train control module (PCM). The PCM controls thevacuum to the throttle actuator through the speedcontrol vacuum and vent solenoids. Refer to Group8H for speed control information.

TACHOMETER—PCM OUTPUTThe powertrain control module (PCM) supplies en-

gine rpm values to the instrument cluster tachometer(if equipped). Refer to Group 8E for tachometer infor-mation.

TORQUE CONVERTER CLUTCH RELAY—PCMOUTPUT

ALL 2.5L 4 CYL. WITH 3-SPEED AUTO. TRANS

4.0L 6 CYL. YJ MODELS WITH 3-SPEED AUTO.TRANS

The transmission mounted torque converter clutch(TCC) solenoid is used to control the torque con-verter. The solenoid is controlled through the power-train control module (PCM) and by the TCC relay.This relay is used only on vehicles equipped with a3-speed automatic transmission.

An electrical output signal is sent from the PCM tothe TCC relay after the PCM receives informationfrom the vehicle speed, MAP, throttle position andengine coolant temperature sensors. After the TCCrelay receives this necessary information, it will senda signal to the torque converter clutch solenoid tocontrol the torque converter.

On YJ models the TCC relay is located in the en-gine compartment, on the cowl panel and near thebattery (Fig. 26). On XJ models the TCC relay is lo-cated in the power distribution center (PDC) (Fig.25).

AIR CLEANERThe air cleaner assembly used on all models (Figs.

27 or 28) is open to ambient air. The blend air doorand vacuum motor that was used on engines of pre-vious model years to supply heated air, is no longerused. The air cleaner housing contains the engine aircleaner element.


Fig. 26 TCC Relay Location—YJ Models


The powertrain control module (PCM) monitors airtemperature in the intake manifold through the in-take manifold air temperature sensor. The PCM ad-justs injector pulse width and ignition timing tocompensate for intake manifold air temperature. Re-fer to Powertrain Control Module (PCM) for more in-formation.

For removal and installation procedures of both theair cleaner housing and the air cleaner element, referto the Component Removal/Installation section ofthis group

OPEN LOOP/CLOSED LOOP MODES OFOPERATION

As input signals to the powertrain control module(PCM) change, the PCM adjusts its response to theoutput devices. For example, the PCM must calculatedifferent injector pulse width and ignition timing foridle than it does for wide open throttle (WOT). Thereare several different modes of operation that deter-mine how the PCM responds to the various input sig-nals.

MODES• Open Loop• Closed Loop

During Open Loop modes, the powertrain controlmodule (PCM) receives input signals and responds

only according to preset PCM programming. Inputfrom the oxygen (O2S) sensor is not monitored dur-ing Open Loop modes.

During Closed Loop modes, the PCM will monitorthe oxygen (O2S) sensor input. This input indicatesto the PCM whether or not the calculated injectorpulse width results in the ideal air-fuel ratio. Thisratio is 14.7 parts air-to-1 part fuel. By monitoringthe exhaust oxygen content through the O2S sensor,the PCM can fine tune the injector pulse width. Thisis done to achieve optimum fuel economy combinedwith low emission engine performance.

The fuel injection system has the following modesof operation:• Ignition switch ON• Engine start-up (crank)• Engine warm-up• Idle• Cruise• Acceleration• Deceleration• Wide open throttle (WOT)• Ignition switch OFF

The ignition switch On, engine start-up (crank), en-gine warm-up, acceleration, deceleration and wideopen throttle modes are Open Loop modes. The idleand cruise modes, (with the engine at operating tem-perature) are Closed Loop modes.

IGNITION SWITCH (KEY-ON) MODEThis is an Open Loop mode. When the fuel system

is activated by the ignition switch, the following ac-tions occur:

Fig. 27 Air Cleaner—XJ Models—Typical

Fig. 28 Air Cleaner—YJ Models—Typical


• The powertrain control module (PCM) pre-posi-tions the idle air control (IAC) motor.• The PCM determines atmospheric air pressurefrom the MAP sensor input to determine basic fuelstrategy.• The PCM monitors the engine coolant temperaturesensor input. The PCM modifies fuel strategy basedon this input.• Intake manifold air temperature sensor input ismonitored• Throttle position sensor (TPS) is monitored• The auto shutdown (ASD) relay is energized by thePCM for approximately three seconds.• The fuel pump is energized through the fuel pumprelay by the PCM. The fuel pump will operate for ap-proximately three seconds unless the engine is oper-ating or the starter motor is engaged• The O2S sensor heater element is energizedthrough the fuel pump relay. The O2S sensor input isnot used by the PCM to calibrate air-fuel ratio dur-ing this mode of operation.• The up-shift indicator lamp is illuminated (manualtransmission only).

ENGINE START-UP MODEThis is an Open Loop mode. The following actions

occur when the starter motor is engaged.The powertrain control module (PCM) receives in-

puts from:• Battery voltage• Engine coolant temperature sensor• Crankshaft position sensor• Intake manifold air temperature sensor• Manifold absolute pressure (MAP) sensor• Throttle position sensor (TPS)• Starter motor relay• Camshaft position sensor signal

The PCM monitors the crankshaft position sensor.If the PCM does not receive a crankshaft positionsensor signal within 3 seconds of cranking the en-gine, it will shut down the fuel injection system.

The fuel pump is activated by the PCM throughthe fuel pump relay.

Voltage is applied to the fuel injectors with thePCM. The PCM will then control the injection se-quence and injector pulse width by turning theground circuit to each individual injector on and off.

The PCM determines the proper ignition timing ac-cording to input received from the crankshaft posi-tion sensor.

ENGINE WARM-UP MODEThis is an Open Loop mode. During engine warm-

up, the powertrain control module (PCM) receives in-puts from:• Battery voltage• Crankshaft position sensor• Engine coolant temperature sensor

• Intake manifold air temperature sensor• Manifold absolute pressure (MAP) sensor• Throttle position sensor (TPS)• Camshaft position sensor signal (in the distribu-tor)• Park/neutral switch (gear indicator signal—auto.trans. only)• Air conditioning select signal (if equipped)• Air conditioning request signal (if equipped)

Based on these inputs the following occurs:• Voltage is applied to the fuel injectors with thepowertrain control module (PCM). The PCM willthen control the injection sequence and injector pulsewidth by turning the ground circuit to each individ-ual injector on and off.• The PCM adjusts engine idle speed through theidle air control (IAC) motor and adjusts ignition tim-ing.• The PCM operates the A/C compressor clutchthrough the clutch relay. This is done if A/C has beenselected by the vehicle operator and requested by theA/C thermostat.• If the vehicle has a manual transmission, the up-shift lamp is operated by the PCM.• When engine has reached operating temperature,the PCM will begin monitoring O2S sensor input.The system will then leave the warm-up mode and gointo closed loop operation.

IDLE MODEWhen the engine is at operating temperature, this

is a Closed Loop mode. At idle speed, the powertraincontrol module (PCM) receives inputs from:• Air conditioning select signal (if equipped)• Air conditioning request signal (if equipped)• Battery voltage• Crankshaft position sensor• Engine coolant temperature sensor• Intake manifold air temperature sensor• Manifold absolute pressure (MAP) sensor• Throttle position sensor (TPS)• Camshaft position sensor signal (in the distribu-tor)• Battery voltage• Park/neutral switch (gear indicator signal—auto.trans. only)• Oxygen sensor

Based on these inputs, the following occurs:• Voltage is applied to the fuel injectors with thepowertrain control module (PCM). The PCM willthen control injection sequence and injector pulsewidth by turning the ground circuit to each individ-ual injector on and off.• The PCM monitors the O2S sensor input and ad-justs air-fuel ratio by varying injector pulse width. Italso adjusts engine idle speed through the idle aircontrol (IAC) motor.


• The PCM adjusts ignition timing by increasingand decreasing spark advance.• The PCM operates the A/C compressor clutchthrough the clutch relay. This happens if A/C hasbeen selected by the vehicle operator and requestedby the A/C thermostat.

The optional Extended Idle Switch is used to raisethe engine idle speed to approximately 1000 rpm.This is when the shifter is in either the Park or Neu-tral position. A rocker-type 2-wire switch (extendedidle switch) is mounted to the instrument panel. Thisswitch will supply a ground circuit to the powertraincontrol module (PCM). The switch is availableonly with 4.0L engine when supplied with theoptional police package.

CRUISE MODEWhen the engine is at operating temperature, this

is a Closed Loop mode. At cruising speed, the power-train control module (PCM) receives inputs from:• Air conditioning select signal (if equipped)• Air conditioning request signal (if equipped)• Battery voltage• Engine coolant temperature sensor• Crankshaft position sensor• Intake manifold air temperature sensor• Manifold absolute pressure (MAP) sensor• Throttle position sensor (TPS)• Camshaft position sensor signal (in the distribu-tor)• Park/neutral switch (gear indicator signal—auto.trans. only)• Oxygen (O2S) sensor

Based on these inputs, the following occurs:• Voltage is applied to the fuel injectors with thePCM. The PCM will then adjust the injector pulsewidth by turning the ground circuit to each individ-ual injector on and off.• The PCM monitors the O2S sensor input and ad-justs air-fuel ratio. It also adjusts engine idle speedthrough the idle air control (IAC) motor.• The PCM adjusts ignition timing by turning theground path to the coil on and off.• The PCM operates the A/C compressor clutchthrough the clutch relay. This happens if A/C hasbeen selected by the vehicle operator and requestedby the A/C thermostat.

ACCELERATION MODEThis is an Open Loop mode. The powertrain control

module (PCM) recognizes an abrupt increase inthrottle position or MAP pressure as a demand forincreased engine output and vehicle acceleration. ThePCM increases injector pulse width in response to in-creased throttle opening.

DECELERATION MODEWhen the engine is at operating temperature, this

is an Open Loop mode. During hard deceleration, thepowertrain control module (PCM) receives the follow-ing inputs.• Air conditioning select signal (if equipped)• Air conditioning request signal (if equipped)• Battery voltage• Engine coolant temperature sensor• Crankshaft position sensor• Intake manifold air temperature sensor• Manifold absolute pressure (MAP) sensor• Throttle position sensor (TPS)• Camshaft position sensor signal (in the distribu-tor)• Park/neutral switch (gear indicator signal—auto.trans. only)

If the vehicle is under hard deceleration with theproper rpm and closed throttle conditions, the PCMwill ignore the oxygen sensor input signal. The PCMwill enter a fuel cut-off strategy in which it will notsupply battery voltage to the injectors. If a hard de-celeration does not exist, the PCM will determine theproper injector pulse width and continue injection.

Based on the above inputs, the PCM will adjust en-gine idle speed through the idle air control (IAC) mo-tor.

The PCM adjusts ignition timing by turning theground path to the coil on and off.

The PCM opens the ground circuit to the A/Cclutch relay to disengage the A/C compressor clutch.This is done until the vehicle is no longer under de-celeration (if the A/C system is operating).

WIDE OPEN THROTTLE MODEThis is an Open Loop mode. During wide open

throttle operation, the powertrain control module(PCM) receives the following inputs.• Battery voltage• Crankshaft position sensor• Engine coolant temperature sensor• Intake manifold air temperature sensor• Manifold absolute pressure (MAP) sensor• Throttle position sensor (TPS)• Camshaft position sensor signal (in the distribu-tor)

During wide open throttle conditions, the followingoccurs:• Voltage is applied to the fuel injectors with thepowertrain control module (PCM). The PCM willthen control the injection sequence and injector pulsewidth by turning the ground circuit to each individ-ual injector on and off. The PCM ignores the oxygensensor input signal and provides a predeterminedamount of additional fuel. This is done by adjustinginjector pulse width.• The PCM adjusts ignition timing by turning theground path to the coil on and off.


• The PCM opens the ground circuit to the A/Cclutch relay to disengage the A/C compressor clutch.This will be done for approximately 15 seconds (if theair conditioning system is operating).

If the vehicle has a manual transmission, the up-shift lamp is operated by the PCM.

IGNITION SWITCH OFF MODEWhen ignition switch is turned to OFF position,

the PCM stops operating the injectors, ignition coil,ASD relay and fuel pump relay.

THROTTLE BODYFiltered air from the air cleaner enters the intake

manifold through the throttle body (Fig. 29). Fueldoes not enter the intake manifold through the throt-tle body. Fuel is sprayed into the manifold by the fuelinjectors. The throttle body is mounted on the intakemanifold. It contains an air control passage (Fig. 30)controlled by an Idle Air Control (IAC) motor. The aircontrol passage is used to supply air for idle condi-tions. A throttle valve (plate) is used to supply air forabove idle conditions.

The throttle position sensor (TPS) and idle air con-trol (IAC) motor are attached to the throttle body.The accelerator pedal cable, speed control cable andtransmission control cable (when equipped) are con-nected to the throttle arm.

A (factory adjusted) set screw is used to mechani-cally limit the position of the throttle body throttleplate. Never attempt to adjust the engine idlespeed using this screw. All idle speed functions arecontrolled by the PCM.

FUEL RAILThe fuel rail supplies fuel to the injectors and is

mounted to the intake manifold (Fig. 31). The fuelpressure regulator is attached to the rail and the fuelpressure test port is integral with the rail. The fuelrail is not repairable.

FUEL PRESSURE REGULATORThe fuel pressure regulator (Fig. 32) is a mechani-

cal device that is not controlled by the powertraincontrol module (PCM).

Fig. 29 Throttle Body—Typical

Fig. 30 Idle Air Control Passage

Fig. 31 Fuel Rail—Typical

Fig. 32 Fuel Pressure Regulator—Typical


The fuel pressure regulator used is a vacuum bal-anced, nonadjustable type. The regulator is mountedon the output end of the fuel rail and is connected tointake manifold vacuum. The fuel return tube (to thefuel tank) is connected to the fuel pressure regulator.

The regulator is calibrated to maintain fuel systempressure at approximately 214 kPa (31 psi). This iswith vacuum applied while the engine is at idle. Fuelpressure will be 55-69 kPa (8-10 psi) higher if vac-uum is not applied to the regulator.

The pressure regulator contains a diaphragm, cali-brated spring and a fuel return valve (Fig. 33). Fuelpressure operates on one side of the regulator, whilespring pressure and intake manifold vacuum operateon the other side. Spring pressure on one side of thediaphragm tries to force the return valve closed. Fuelpressure on other side of diaphragm, with assistancefrom manifold vacuum on spring side of diaphragm,act against spring pressure to open the return valve.System fuel pressure is the amount of fuel pressurerequired to force against spring pressure and unseatthe return valve.

Without vacuum applied to the spring side of theregulator, the spring is calibrated to open the fuel re-turn outlet. This happens when the pressure differ-ential between the fuel injectors and the intakemanifold reaches approximately 269 kPa (39 psi).Since manifold vacuum varies with engine operatingconditions, the amount of vacuum applied to thespring side of the diaphragm varies. For this reason,fuel pressure varies, depending upon intake manifoldvacuum. With low vacuum, such as during wide open

throttle conditions, minimal vacuum assistance isavailable. Full spring pressure is exerted to seal thefuel outlet. This causes the system pressure to in-crease. With high vacuum, such as at engine idle orduring vehicle deceleration, fuel pressure on one sideof the diaphragm is balanced by intake manifoldpressure. This is done on the spring side of the dia-phragm and results in lower system fuel pressure.

Fig. 33 Fuel Pressure Regulator Operation—Typical


MULTI-PORT FUEL INJECTION (MFI)—GENERAL DIAGNOSIS

INDEX

page page

Automatic Shutdown (ASD) Relay Testing . . . . . . . 46Camshaft Position Sensor Test . . . . . . . . . . . . . . . 46Crankshaft Position Sensor Test . . . . . . . . . . . . . . 47Diagnostic Trouble Code (DTC) . . . . . . . . . . . . . . . 54DRB Scan Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . 54Engine Coolant Temperature Sensor Test . . . . . . . 46Extended Idle Switch Test . . . . . . . . . . . . . . . . . . . 48Fuel Injector Test . . . . . . . . . . . . . . . . . . . . . . . . . 51Fuel Pump Relay Testing . . . . . . . . . . . . . . . . . . . 47Fuel System Pressure Test . . . . . . . . . . . . . . . . . . 51General Information . . . . . . . . . . . . . . . . . . . . . . . 35Idle Air Control Motor Test . . . . . . . . . . . . . . . . . . . 49Intake Manifold Air Temperature Sensor Test . . . . . 46

Manifold Absolute Pressure (Map) Sensor Test . . . 47On-Board Diagnostics (OBD) . . . . . . . . . . . . . . . . . 51Oxygen Sensor (O2S) Heating Element Test . . . . . 48Pcm System Schematics . . . . . . . . . . . . . . . . . . . . 41Powertrain Control Module (PCM) 60-Way

Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Relays—Operation/Testing . . . . . . . . . . . . . . . . . . 50Starter Motor Relay Test . . . . . . . . . . . . . . . . . . . . 51Throttle Position Sensor (TPS) Test . . . . . . . . . . . . 48Torque Converter Clutch Relay Test . . . . . . . . . . . . 48Vehicle Speed Sensor Test . . . . . . . . . . . . . . . . . . 48Visual Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . 35

GENERAL INFORMATIONAll 2.5L 4-cylinder and 4.0L 6-cylinder engines are

equipped with sequential Multi-Port Fuel Injection(MFI). The MFI system provides precise air/fuel ra-tios for all driving conditions.

VISUAL INSPECTIONA visual inspection for loose, disconnected, or incor-

rectly routed wires and hoses should be made. Thisshould be done before attempting to diagnose or ser-vice the fuel injection system. A visual check willhelp spot these faults and save unnecessary test anddiagnostic time. A thorough visual inspection will in-clude the following checks:

(1) Verify that the 60-way connector is fully in-serted into the connector of the powertrain controlmodule (PCM) (Figs. 1 or 2). Verify that the connec-tor mounting bolt is tightened to 4 Nzm (35 in. lbs.)torque.

(2) Inspect the battery cable connections. Be surethey are clean and tight.

(3) Inspect fuel pump relay and air conditioningcompressor clutch relay (if equipped). Inspect ASDrelay and radiator fan relay (if equipped) connec-tions. Inspect starter motor relay connections. In-spect relays for signs of physical damage andcorrosion. The relays are installed in the power dis-tribution center (PDC) (Figs. 3 or 4).

(4) Inspect ignition coil connections. Verify that coilsecondary cable is firmly connected to coil (Figs. 5 or6).

(5) Verify that distributor cap is correctly attachedto distributor. Be sure that spark plug cables arefirmly connected to the distributor cap and the sparkplugs in their correct firing order. Be sure that coilcable is firmly connected to distributor cap and coil.Be sure that camshaft position sensor wire connectoris firmly connected to harness connector (Figs. 7 or8). Inspect spark plug condition. Refer to Group 8D,Fig. 1 PCM—YJ Models

Fig. 2 PCM—XJ Models

J FUEL SYSTEM GENERAL DIAGNOSIS 14 - 35

Ignition System. Connect vehicle to an oscilloscopeand inspect spark events for fouled or damaged sparkplugs or cables.

(6) Verify that generator output wire, generatorconnector and ground wire are firmly connected tothe generator (Fig. 9).

Fig. 3 PDC—YJ Models


Fig. 5 Ignition Coil—2.5L Engine—Typical

Fig. 6 Ignition Coil—4.0L Engine—Typical

Fig. 7 Distributor and Wiring—2.5L Engine—Typical

Fig. 8 Distributor and Wiring—4.0L Engine—Typical

14 - 36 FUEL SYSTEM GENERAL DIAGNOSIS J

(7) Inspect the system ground connections at theengine (Fig. 10). For location of system grounds, referto Group 8, Wiring.

(8) Verify that crankcase ventilation (CCV) freshair hose is firmly connected to cylinder head and aircleaner covers (Figs. 11 or 12).

(9) Verify that vacuum hose is firmly connected tofuel pressure regulator and manifold fitting (Figs. 13or 14).

(10) Inspect fuel tube quick-connect fitting-to-fuelrail connections (Fig. 15).

(11) Verify that hose connections to all ports of vac-uum fittings on intake manifold are tight and notleaking.

(12) Inspect accelerator cable, transmission throt-tle cable (if equipped) and cruise control cable con-nections (if equipped). Check their connections to thethrottle arm of throttle body for any binding or re-strictions (Fig. 16).

(13) If equipped with vacuum brake booster, verifythat vacuum booster hose is firmly connected to fit-

ting on intake manifold. Also check connection tobrake vacuum booster (Fig. 17).

(14) On XJ models equipped with: a 4.0L 6-cylin-der engine, heavy duty cooling system and/or A/C,

Fig. 9 Generator Connector and Output WireConnections—Typical

Fig. 10 System Ground Connections—Typical

Fig. 11 CCV System—2.5L Engine

Fig. 12 CCV System—4.0L Engine

Fig. 13 Pressure Regulator Vacuum Hose—2.5LEngine


verify that auxiliary radiator cooling fan wire connec-tor is firmly connected to harness.

(15) Inspect the air cleaner inlet and air cleaner el-ement for restrictions.

(16) Inspect radiator grille area, radiator fins andair conditioning condenser for restrictions.

(17) Verify that intake manifold air temperaturesensor wire connector is firmly connected to harnessconnector (Figs. 18 or 19).

Fig. 14 Pressure Regulator Vacuum Hose—4.0LEngine

Fig. 15 Fuel Supply Tube—Typical

Fig. 16 Throttle Body Cables—Typical

Fig. 17 Brake Vacuum Booster Hose—Typical




(18) Inspect engine ground strap connections atdash panel and rear cylinder head bolt (Fig. 20). Forground locations, refer to Group 8, Wiring.

(19) Verify that MAP sensor electrical connector isfirmly connected to MAP sensor (Fig. 21). Verify thatvacuum hose is firmly connected to MAP sensor andto the intake manifold.

(20) Verify that fuel injector wire harness connec-tors are firmly connected to the fuel injectors in thecorrect order. Each harness connector is tagged withthe number of its corresponding fuel injector (Fig.22).

(21) Verify that harness connectors are firmly con-nected to idle air control (IAC) motor and throttle po-sition sensor (TPS) (Figs. 18, 19 or 23).

(22) Verify that wire harness connector is firmlyconnected to the engine coolant temperature sensor(Fig. 24).

(23) Verify that oxygen sensor wire connector isfirmly connected to the sensor. Inspect sensor andconnector for damage (Fig. 25).

(24) Raise and support the vehicle.

(25) Inspect for pinched or leaking fuel tubes. In-spect for pinched cracked or leaking fuel hoses.

(26) Inspect for exhaust system restrictions suchas pinched exhaust pipes, collapsed muffler or

Fig. 20 Engine Ground Strap Connections—Typical

Fig. 21 MAP Sensor—Typical

Fig. 22 Fuel Injector Wire Harness—Typical

Fig. 23 IAC Motor and TPS—2.5L Engine



plugged catalytic convertor.(27) If equipped with automatic transmission, ver-

ify that electrical harness is firmly connected to park/neutral safety switch. Refer to AutomaticTransmission section of Group 21.

(28) Verify that the harness connector is firmlyconnected to the vehicle speed sensor (Fig. 26).

(29) Verify that fuel pump module wire connectoris firmly connected to harness connector.

(30) Inspect fuel hoses at fuel pump module forcracks or leaks (Fig. 27).

(31) Inspect transmission torque convertor housing(automatic transmission) or clutch housing (manualtransmission) for damage to timing ring on driveplate/flywheel.

(32) Verify that battery cable and solenoid feedwire connections to the starter solenoid are tight and

clean. Inspect for chaffed wires or wires rubbing upagainst other components (Fig. 28).

POWERTRAIN CONTROL MODULE (PCM) 60-WAYCONNECTOR

For PCM 60-way connector wiring schematics, referto Group 8W, Wiring Diagrams.

Fig. 27 Fuel Pump Module Connector and Fuel Hoses—Typical

Fig. 25 Oxygen Sensor Location—Typical

Fig. 26 Vehicle Speed Sensor—Typical


PCM SYSTEM SCHEMATICSPowertrain control system schematics for the 2.5L

4-cylinder and 4.0L 6-cylinder engines are shown infigures 29, 30, 31 and 32.

These schematics are displayed as a quick refer-ence only. They are not intended to be all-inclusive.Refer to the Wiring Diagrams section for detailed in-formation.

Fig. 28 Starter Solenoid Connections—Typical


Fig

.29

Sys

tem

Sch

emat

ic—

YJ

Mod

els

with

2.5L

Eng

ine


Fig

.30

Sys

tem

Sch

emat

ic—

YJ

Mod

els

with

4.0L

Eng

ine


Fig

.31

Sys

tem

Sch

emat

ic—

XJ

Mod

els

with

2.5L

Eng

ine


Fig

.32

Sys

tem

Sch

emat

ic—

XJ

Mod

els

with

4.0L

Eng

ine


AUTOMATIC SHUTDOWN (ASD) RELAY TESTINGTo perform a complete test of the ASD relay and its

circuitry, refer to the DRB scan tool and appropriatePowertrain Diagnostics Procedures manual. To testthe relay only, refer to Relays—Operation/Testing inthis section of the group.

CAMSHAFT POSITION SENSOR TESTRefer to Group 8D, Ignition Systems, for Camshaft

Position Sensor testing.

ENGINE COOLANT TEMPERATURE SENSOR TESTTo perform a complete test of the engine coolant

temperature sensor and its circuitry, refer to DRBscan tool and appropriate Powertrain DiagnosticsProcedures manual. To test the sensor only, refer tothe following:

Disconnect wire harness connector from enginecoolant temperature sensor (Fig. 33).

Test the resistance of the sensor with a high inputimpedance (digital) volt-ohmmeter. The resistanceshould be less than 1000 ohms with the engine at itscorrect operating temperature. Refer to the CoolantTemperature Sensor/Manifold Air Temperature Sen-sor resistance chart. Replace the sensor if it is notwithin the range of resistance specified in the chart.

Test continuity of the wire harness. Do this be-tween the Powertrain Control Module (PCM) wireharness connector terminal-2 and the sensor connec-tor terminal. Also test continuity of wire harness ter-minal-4 to the sensor connector terminal. Repair thewire harness if an open circuit is indicated.

INTAKE MANIFOLD AIR TEMPERATURE SENSORTEST

To perform a complete test of the sensor and its cir-cuitry, refer to DRB scan tool and appropriate Pow-

ertrain Diagnostics Procedures manual. To test thesensor only, refer to the following:

Disconnect the wire harness connector from the in-take manifold air temperature sensor (Figs. 34 or35).

Test the resistance of the sensor with an input im-pedance (digital) volt-ohmmeter. The resistanceshould be less than 4000 ohms with the engine at op-erating temperature. The longer the engine idles, thewarmer the intake manifold temperature will be-come. Refer to the Coolant Temperature Sensor/Man-ifold Air Temperature Sensor resistance chart.Replace the sensor if it is not within the range of re-sistance specified in the chart.


SENSOR RESISTANCE (OHMS)—COOLANTTEMPERATURE SENSOR/MANIFOLD AIR

TEMPERATURE

Fig. 34 Air Temperature Sensor—2.5L Engine


Test the resistance of the wire harness. Do this be-tween the powertrain control module (PCM) wireharness connector terminal-2 and the sensor connec-tor terminal. Also test terminal-4 to the sensor con-nector terminal. Repair the wire harness asnecessary if the resistance is greater than 1 ohm.

FUEL PUMP RELAY TESTINGFor testing this relay, refer to Relays—Operation/

Testing in this section of the group.

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSORTEST

To perform a complete test of the MAP sensor andits circuitry, refer to DRB scan tool and appropriatePowertrain Diagnostics Procedures manual. To testthe sensor only, refer to the following:

Inspect the MAP sensor vacuum hose connectionsat the throttle body and sensor. Repair as necessary.

CAUTION: When testing, do not remove the electri-cal connector from MAP sensor (Fig. 36). Be surethat the MAP sensor harness wires are not dam-aged by the test meter probes.

Test the MAP sensor output voltage at the MAPsensor connector between terminals A and B (asmarked on the sensor body) (Fig. 37). With the igni-tion switch ON and the engine OFF, output voltageshould be 4-to-5 volts. The voltage should drop to 1.5-to-2.1 volts with a neutral-hot idle speed condition.

Test the powertrain control module (PCM) (termi-nal-5) for the same voltage described above to verifythe wire harness condition. Repair as necessary.

Test MAP sensor supply voltage at sensor connec-tor between terminals A and C (Fig. 37) with the ig-nition ON and engine OFF. The voltage should beapproximately 5 volts (60.5V). Five volts (60.5V)

should also be at terminal-6 of the PCM wire harnessconnector. Repair or replace the wire harness as nec-essary.

Test the MAP sensor ground circuit at sensor con-nector terminal-A (Fig. 37) and PCM connector termi-nal-4. Repair the wire harness if necessary.

Test the MAP sensor ground circuit at the PCMconnector between terminal-4 and terminal-11 withan ohmmeter. If the ohmmeter indicates an open cir-cuit, inspect for a defective sensor ground connection.Refer to Group 8W, Wiring for location of enginegrounds. If the ground connection is good, replace thePCM. If terminal-4 has a short circuit to 12 volts,correct this condition before replacing the PCM.

CRANKSHAFT POSITION SENSOR TESTRefer to Group 8D, Ignition Systems for test proce-

dures.

Fig. 35 Air Temperature Sensor—4.0L Engine Fig. 36 MAP Sensor—Typical

Fig. 37 MAP Sensor Connector Terminals—Typical


EXTENDED IDLE SWITCH TEST

OPTIONAL POLICE PACKAGE ONLY

OPERATIONThe extended idle switch is used to raise the en-

gine idle speed to approximately 1000 rpm when theshifter is in either the Park or Neutral position. Arocker-type 2-wire switch (extended idle switch) ismounted to the instrument panel. This switch isavailable only with 4.0L engine when suppliedwith the optional police package.

TESTINGThe extended idle switch will control a ground cir-

cuit going to the powertrain control module (PCM).When a ground signal (through this switch) has beenreceived at pin number 10 in the PCM, engine idlespeed will increase.

Bring the engine to normal operating temperatureand turn the extended idle switch to the ON position.Engine speed should now increase to approximately1000 rpm when the shifter is in either the Park orNeutral position. If engine speed does not increase,apply a good ground to pin number 10 at the PCMusing a small paper clip. Be careful not to damagethe wiring with the paper clip. If the engine speednow increases, it can be assumed that the PCM isfunctioning correctly. Check the instrument panelmounted switch for a closed ground circuit when inthe ON position. If the engine speed will not increaseafter applying a ground to pin number 10, replacethe PCM. Refer to Group 8W, Wiring Diagrams forcircuit and wiring information.

THROTTLE POSITION SENSOR (TPS) TESTTo perform a complete test of the sensor and its cir-

cuitry, refer to DRB scan tool and appropriate Pow-ertrain Diagnostics Procedures manual. To test thesensor only, refer to the following:

The throttle position sensor (TPS) can be testedwith a digital voltmeter. The center terminal of theTPS is the output terminal (Figs. 38 or 39).

With the ignition key in the ON position, back-probe the TPS connector. Check the TPS output volt-age at the center terminal wire of the connector.Check this at idle (throttle plate closed) and at wideopen throttle (WOT). At idle, TPS output voltageshould must be greater than 200 millivolts. At wideopen throttle, TPS output voltage must be less than4.8 volts. The output voltage should increase gradu-ally as the throttle plate is slowly opened from idle toWOT.

TORQUE CONVERTER CLUTCH RELAY TESTTo test the relay only, refer to Relays—Operation/

Testing in this section of the group. To test thetorque converter clutch circuit and related compo-

nents, refer to the appropriate Powertrain DiagnosticProcedures manual for operation of the DRB scantool.

VEHICLE SPEED SENSOR TESTTo perform a complete test of the sensor and its cir-

cuitry, refer to DRB scan tool and appropriate Pow-ertrain Diagnostics Procedures manual.

OXYGEN SENSOR (O2S) HEATING ELEMENT TESTTo perform a complete test of the O2S sensor (Fig.

40) and its circuitry, refer to DRB scan tool and ap-propriate Powertrain Diagnostics Procedures manual.To test the sensor only, refer to the following:

The oxygen sensor heating element can be testedwith an ohmmeter as follows:

With the sensor at room temperature 25 degrees C(77 degrees F), disconnect the O2S sensor connector.Connect the ohmmeter test leads across the whitewire terminals of the sensor connector. Resistanceshould be between 5 and 7 ohms. Replace the sensorif the ohmmeter displays an infinity (open) reading.

Fig. 38 TPS Testing—2.5L Engine

Fig. 39 TPS Testing—4.0L Engine


IDLE AIR CONTROL MOTOR TESTIdle air control (IAC) motor operation can be tested

using special exerciser tool number 7558 (Fig. 41).

CAUTION: Proper safety precautions must be takenwhen testing the idle air control motor:

• Set the parking brake and block the drive wheels• Route all tester cables away from the cooling fans,drive belt, pulleys and exhaust components• Provide proper ventilation while operating the en-gine• Always return the engine idle speed to normal be-fore disconnecting the exerciser tool

(1) With the ignition OFF, disconnect the IAC mo-tor wire connector at throttle body (Fig. 41).

(2) Plug the exerciser tool number 7558 harnessconnector into the IAC motor.

(3) Connect the red clip of exerciser tool 7558 tobattery positive terminal. Connect the black clip tonegative battery terminal. The red light on the exer-ciser tool will flash when the tool is properly con-nected.

(4) Start engine.When the switch on the tool is in the HIGH or

LOW position, the light on the tool will flash. Thisindicates that voltage pulses are being sent to theIAC stepper motor.

(5) Move the switch to the HIGH position. The en-gine speed should increase. Move the switch to theLOW position. The engine speed should decrease.

(a) If the engine speed changes while using theexerciser tool, the IAC motor is functioning prop-erly. Disconnect the exerciser tool and connect theIAC motor wire connector to the stepper motor.

(b) If the engine speed does not change, turn theignition OFF and proceed to step (6). Do not dis-connect exerciser tool from the IAC motor.(6) Remove the IAC motor from the throttle body.

Do not remove IAC motor housing from throttle body.

CAUTION: When checking IAC motor operation withthe motor removed from the throttle body, do notextend the pintle (Fig. 42) more than 6.35 mm (.250in). If the pintle is extended more than this amount,it may separate from the IAC motor. The IAC motormust be replaced if the pintle separates from themotor.

(7) With the ignition OFF, cycle the exerciser toolswitch between the HIGH and LOW positions. Ob-serve the pintle. The pintle should move in-and-outof the motor.

(a) If the pintle does not move, replace the idleair control motor. Start the engine and test the re-placement motor operation as described in step (5).

(b) If the pintle operates properly, check the idleair control motor bore in the throttle body bore forblockage and clean as necessary. Reinstall the idleair control motor and retest. If blockage is notfound, refer to the DRB scan tool and the appropri-ate Powertrain Diagnostics Procedures servicemanual.

Fig. 40 Oxygen Sensor—Typical

Fig. 41 IAC Motor Testing—Typical

Fig. 42 Idle Air Control (IAC) Motor Pintle


RELAYS—OPERATION/TESTING

OPERATIONThe following operations/tests apply to these

relays only: automatic shutdown (ASD), fuel pumpand torque converter clutch. For operations/tests onall other relays, refer to the appropriate section ofthis service manual.

The relay terminal numbers from (Fig. 43) can befound on the bottom of the relay:• Terminal number 30 is connected to battery volt-age and can be switched or B+ (hot) at all times.• Terminal number 87A is connected (a circuit isformed) to terminal 30 in the de-energized (normallyOFF) position.• Terminal number 87 is connected (a circuit isformed) to terminal 30 in the energized (ON) posi-tion. Terminal number 87 then supplies battery volt-age to the component being operated.• Terminal number 86 is connected to a switched (+)power source.• Terminal number 85 is grounded by the power-train control module (PCM).

TESTING(1) Remove relay before testing.

(2) Using an ohmmeter, perform a resistance testbetween terminals 85 and 86. Resistance value(ohms) should be 75 65 ohms for resistor equippedrelays.

(3) Connect the ohmmeter between terminals num-ber 87A and 30. Continuity should be present at thistime.

(4) Connect the ohmmeter between terminals num-ber 87 and 30. Continuity should not be present atthis time.

(5) Use a set of jumper wires (16 gauge or small-er). Connect one jumper wire between terminal num-ber 85 (on the relay) to the ground side (-) of a 12Volt power source.

(6) Attach the other jumper wire to the positiveside (+) of a 12V power source. Do not connect thejumper wire to relay at this time.

CAUTION: DO NOT ALLOW THE OHMMETER TOCONTACT TERMINALS 85 OR 86 DURING THESETESTS. DAMAGE TO OHMMETER MAY RESULT.

(7) Attach the other jumper wire (12V +) to termi-nal number 86. This will activate the relay. Continu-ity should now be present between terminals number87 and 30. Continuity should not be present betweenterminals number 87A and 30.

Fig. 43 Relay Terminals


(8) Disconnect jumper wires from relay and 12 Voltpower source.

If continuity or resistance tests did not pass, re-place relay. If tests passed, refer to Group 8W, WiringDiagrams for additional circuit information. Also re-fer to the appropriate Powertrain Diagnostic Proce-dures manual for operation of the DRB scan tool.

STARTER MOTOR RELAY TESTRefer to Group 8A, Battery/Starting/Charging/Sys-

tem Diagnostics, for starter motor relay testing.

FUEL INJECTOR TESTTo perform a complete test of the fuel injectors and

their circuitry, refer to DRB scan tool and appropri-ate Powertrain Diagnostics Procedures manual. Totest the injector only, refer to the following:

Disconnect the injector wire connector from the in-jector. Place an ohmmeter on the injector terminals.Resistance reading should be approximately 14.5ohms 61.2 ohms at 20°C (68°F). Proceed to the fol-lowing Injector Diagnosis chart. When performingthe following tests from the chart, do not leaveelectrical current applied to the injector forlonger than five seconds. Damage to injectorcoil or internal injector seals could result.

FUEL SYSTEM PRESSURE TESTRefer to the Fuel Delivery System section of this

group. See Fuel System Pressure Test.

ON-BOARD DIAGNOSTICS (OBD)The powertrain control module (PCM) has been

programmed to monitor many different circuits of thefuel injection system. If a problem is sensed in amonitored circuit often enough to indicate an actualproblem, a Diagnostic Trouble Code (DTC) is stored.The DTC will be stored in the PCM memory for even-tual display to the service technician. If the problemis repaired or ceases to exist, the PCM cancels theDTC after 51 engine starts.

Certain criteria must be met for a diagnostic trou-ble code (DTC) to be entered into PCM memory. Thecriteria may be a specific range of engine rpm, enginetemperature and/or input voltage to the PCM.

It is possible that a DTC for a monitored circuitmay not be entered into memory even though a mal-function has occurred. This may happen because oneof the DTC criteria for the circuit has not been met.Example: assume that one of the criteria for theMAP sensor circuit is that the engine must be oper-ating between 750 and 2000 rpm to be monitored fora DTC. If the MAP sensor output circuit shorts toground when the engine rpm is above 2400 rpm, a 0volt input will be seen by the PCM. A DTC will notbe entered into memory because the condition doesnot occur within the specified rpm range.

A DTC indicates that the powertrain control mod-ule (PCM) has recognized an abnormal signal in acircuit or the system. A DTC may indicate the resultof a failure, but never identify the failed componentdirectly.

There are several operating conditions that thePCM does not monitor and set a DTC for. Refer tothe following Monitored Circuits and Non-MonitoredCircuits in this section.

MONITORED CIRCUITSThe powertrain control module (PCM) can detect

certain problems in the fuel injection system.Open or Shorted Circuit - The PCM can deter-

mine if sensor output (which is the input to PCM) iswithin proper range. It also determines if the circuitis open or shorted.

Output Device Current Flow - The PCM senseswhether the output devices are hooked up.

If there is a problem with the circuit, the PCMsenses whether the circuit is open, shorted to ground(-), or shorted to (+) voltage.

Oxygen Sensor - The PCM can determine if theoxygen sensor is switching between rich and lean.This is, once the system has entered Closed Loop. Re-fer to Open Loop/Closed Loop Modes Of Operation inthe Component Description/System Operation sectionfor an explanation of Closed (or Open) Loop opera-tion.

NON-MONITORED CIRCUITSThe PCM does not monitor the following circuits,

systems or conditions that could have malfunctionsthat result in driveability problems. A DiagnosticTrouble Code (DTC) may not be displayed for theseconditions.

Fuel Pressure: Fuel pressure is controlled by thevacuum assisted fuel pressure regulator. The PCMcannot detect a clogged fuel pump inlet filter, cloggedin-line fuel filter, or a pinched fuel supply or return

Fig. 44 Fuel Injector Internal Components—Typical


INJECTOR DIAGNOSIS—VEHICLE RUNS ROUGH AND/OR HAS A MISS


line. However, these could result in a rich or leancondition causing an oxygen sensor DTC to be storedin the PCM.

Secondary Ignition Circuit: The PCM cannotdetect an inoperative ignition coil, fouled or wornspark plugs, ignition cross firing, or open circuitedspark plug cables.

Engine Timing: The PCM cannot detect an incor-rectly indexed timing chain, camshaft sprocket orcrankshaft sprocket. The PCM also cannot detect anincorrectly indexed distributor. However, these couldresult in a rich or lean condition causing an oxygensensor DTC to be stored in the PCM.

Cylinder Compression: The PCM cannot detectuneven, low, or high engine cylinder compression.

Exhaust System: The PCM cannot detect aplugged, restricted or leaking exhaust system.

Fuel Injector Malfunctions: The PCM cannot de-termine if the fuel injector is clogged, or the wronginjector is installed. However, these could result in arich or lean condition causing an oxygen sensor DTCto be stored in the PCM.

Excessive Oil Consumption: Although the PCMmonitors exhaust stream oxygen content through ox-ygen sensor (closed loop), it cannot determine exces-sive oil consumption.

Throttle Body Air Flow: The PCM cannot detecta clogged or restricted air cleaner inlet or air cleanerelement.

Evaporative System: The PCM will not detect arestricted, plugged or loaded EVAP canister.

Vacuum Assist: Leaks or restrictions in the vac-uum circuits of vacuum assisted engine control sys-tem devices are not monitored by the PCM. However,a vacuum leak at the MAP sensor will be monitoredand a diagnostic trouble code (DTC) will be gener-ated by the PCM.

Powertrain Control Module (PCM) SystemGround: The PCM cannot determine a poor systemground. However, a DTC may be generated as a re-sult of this condition.

Powertrain Control Module (PCM) ConnectorEngagement: The PCM cannot determine spread ordamaged connector pins. However, a DTC may begenerated as a result of this condition.

HIGH AND LOW LIMITSThe powertrain control module (PCM) compares in-

put signal voltages from each input device. It will es-tablish high and low limits that are programmed intoit for that device. If the input voltage is not withinspecifications and other Diagnostic Trouble Code(DTC) criteria are met, a DTC will be stored in mem-ory. Other DTC criteria might include engine rpmlimits or input voltages from other sensors orswitches. The other inputs might have to be sensedby the PCM when it senses a high or low input volt-age from the control system device in question.

ACCESSING DIAGNOSTIC TROUBLE CODESA stored diagnostic trouble code (DTC) can be dis-

played by cycling the ignition key On-Off-On-Off-Onwithin three seconds and observing the malfunctionindicator lamp. This lamp is displayed on the instru-ment panel as the CHECK ENGINE lamp (Figs. 45or 46).

They can also be displayed through the use of theDiagnostic Readout Box (DRB) scan tool. The DRBscan tool connects to the data link connector in theengine compartment (Figs. 47 or 48). For operation ofthe DRB, refer to the appropriate Powertrain Diag-nostic Procedures service manual.

Fig. 45 Check Engine Lamp—XJ Models—Typical

Fig. 46 Check Engine Lamp—YJ Models—Typical


Documents

MULTI-PORT FUEL INJECTION …billhughes.com/temp/95yjFuel.pdf† Engine coolant temperature sensor † Crankshaft position sensor † Ignition circuit sense (ignition switch in run