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COMPUTERS

ANDINPUT SENSORS

CHAPTER 9

ENGINE PERFORMANCE

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MICROCOMPUTER OPERATION

HAPPENS IN STAGES

Memory

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INPUT STAGE

INPUTS: All

sensors produce

are a voltage

signal of sometype

Some Inputs are

conditioned

before going to themicroprocessor.

Amplification

A/D Conversion

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INPUT CONDITIONING

Microprocessor

can only process

some types ofsignals

Must amplify some

signals

Must convert

analog signals to

digital signals

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BINARY

CODE

A/D converter takes

snapshot of analog

signal

Computers only

understand 1s and

0s.

1 = On

0 = Off

Voltages are

classified into

different ranges

Each range is

assigned a numeric

value

Values are translated

into a binary code

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PROCESSING OPERATION

Digital signal

compared to

lookup tables Information is sent

to microprocessor

Microprocessor

decides what to do

Issues a command

to output actuator

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TYPES OF MEMORY

3 DIFFERENT TYPES

READ ONLY MEMORY (ROM) RANDOM ACCESS MEMORY

(RAM)

KEEP ALIVE MEMORY (KAM)

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READ ONLY MEMORY Permanent memory

Microprocessor can only read

information from ROM

Information cannot be erased

Contains info such as: programs,

look up tables to tell how vehicle

should perform. Data and formulas

used to perform calculations

Vehicle information: # of cylinders,

valve size, transmission type, rear

end

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RANDOM ACCESS

MEMORY Information stored temporarily

Can be written to or read from

When Ignition is turned off, memory

is erased.

Used to store information from

sensors, results of calculations and

data subject to constant change.

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KEEP ALIVE MEMORY

Information can be read, written and

erased from KAM

KAM is not lost when ignition key isturned off

Disconnecting Battery will erase

KAM

KAM allows for adaptive strategies

Stores diagnostic codes

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PROCESSOR LOCATION

Usually under dash or inside car

Sometimes under hood.

Susceptible to water, dirt, dust, heatand vibration

Some are built in to component

Body Computers located manydifferent places in vehicle.

Some cars centrally locate all

processors

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HANDLING THE

PROCESSOR TOUCH THE VEHICLE CHASSIS TO

DISCHARGE STATIC ELECTRICITY

TURN POWER OFF BEFOREDISCONNECTING PROCESSOR

BE SURE DVOM CONNECTIONS ARE

CORRECT

BE SURE TO USE THE CORRECT

TEST INSTRUMENT

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OUTPUT STAGE Microprocessor

issues commands

in the form of

voltages

Can display

information on a

Scanner or Digital

dash Can control

hydraulic, vacuum

or electrical

components.

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OUTPUT DRIVERS

Microprocessor

send digital

signals to output

drivers Drivers usually

do not send

voltage to

actuators Microprocessor

controls actuator

ground circuit

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INPUT SENSORS

ALL SENSORS PERFORM SAME

BASIC FUNCTION

DETECT MECHANICAL CONDITION

(MOVEMENT)

CHEMICAL STATE CHANGE

TEMPERATURE CONDITION

ALL SENSORS CHANGE ABOVEINPUT INTO VOLTAGE SIGNALS

THAT PROCESSOR CAN USE

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3 WIRE SENSORSREFERENCE VOLTAGE SENSOR

OR VOLTAGE MODIFIER

VOLTAGE REFERENCE

SIGNAL WIRE

SIGNAL RETURN (GROUND)

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THROTTLE POSITION

SENSOR

CHANGES MECHANICAL ACTION INTO

ELECTRICAL SIGNAL SOME ARE ADJUSTABLE

SOME READ HIGH VOLTS AT IDLE, SOME

LOW VOLTS AT IDLE

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TWO WIRE SENSORVOLTAGE MODIFIER

SIGNAL CIRCUIT

GROUND CIRCUIT

TWO TYPES OFTERMISTORS

NTC = REDUCES

OHMS WHEN TEMP

INCREASES

PTC = INCREASES

OHMS WHEN TEMP

INCREASES

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MAF SENSOR USES HOT WIRE

PCM MONITORS

COLD WIRE TEMP. SENDS CURRENT

TO HOT WIRE TO

MAINTAIN 392

DEGREES ABOVE

COLD WIRE

AMOUNT OF

CURRENTDETERMINES

INTAKE AIR FLOW

306C

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CYCLE

DUTY CYCLE

PULSE WIDTHFREQUENCY

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PULSE WIDTH

LENGTH OF TIME IN MS, ACTUATOR IS

ON IE, DURATION OF ON-TIME

PULSE WIDTH MODULATION

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VANE AIR FLOW METER

USES THREE

TYPES OF

VOLTAGEMODIFIERS

SWITCH

POTENTIOMETER

THERMISTOR

MOVES DOOR TO

DETERMINE AIR

FLOW305C

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WHEATSTONE BRIDGE

THREE FIXED AND ONE VARIABLE

RESISTOR

PCM ALWAYS TO BALANCE THE

BRIDGE

USED TO MEASURE PRESSURE AND

MECHANICAL STRAIN

285C

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VOLTAGE GENERATOR

GENERATES IT OWN VOLTAGE SIGNAL

COMPARES INSIDE AIR TO OUTSIDE AIR SIGNAL IS .1 TO 1.0 VOLT

LOW VOLTAGE MEANS SENSING LEAN

HIGH VOLTAGE MEANS SENSING RICH

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O2 SENSOR SIGNAL

Signal range is

between 0.0 and

1.0volt Normal operation

is from 0.2 to 0.8

volts

PCM will always tryto do the opposite

from what 02

sensor is signaling 417L

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02 CROSSCOUNTS

Generally, about 2 to 3 crosscounts is normal operation

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ZIRCONIA SENSOR

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TITANIA SENSOR

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DIAGNOSTIC LOGIC TREE

LOGIC TREE OR

DIAGNOSTIC

CHART SOME CHARTS

INCLUDE

EXPLANATIONS

MANYMANUFACTUERS

USE THIS TYPE

DIAGNOSTICS

LOOK UP TABLE USED TO

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LOOK UP TABLE USED TO

DETERMINE BLOCK

LEARN/INTERGRATOR

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SCANNER

SCANNERS READ

CODES AND DATA

STREAMS TEST ACTUATORS

GRAPHING

LAB SCOPE

DVOM

TECHNICAL INFO

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GM PROM

CONTAINS SPECIFIC PROGRAMS SUCH

AS; SPARK ADVANCE, FUEL INJECTION SOME ARE ELECTRONICALLY

ERASABLE

REPLACEABLE SEPARATE FROM PCM

LAB PG 379

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CODE CHART

SELF DIAGNOSTICS

(SELF TEST MODE)

HARD FAULTS

SOFT CODES ORMEMORY CODES

ACCESS TROUBLE

CODES WITH

SCANNER OR BY

MANUAL METHOD

ERASING FAULT

CODES

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THE THREE AMIGOS