Chapter 15

Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman

© 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OBJECTIVES

After studying Chapter 15, the reader should be able to:1. Prepare for ASE Electrical/Electronic Systems

(A6) certification test content area (General Electrical/Electronic Systems Diagnosis).

2. Explain the purpose and function of onboard computers.

3. List the various parts of an automotive computer.4. List five input sensors.5. List four devices controlled by the computer

(output devices).



COMPUTER CONTROL

• Modern automotive control systems consist of a network of electronic sensors, actuators, and computer modules designed to regulate the power train and vehicle support systems.

• A computer processes the input voltage signals it receives by computing what they represent, and then delivering the data in computed or processed form.



THE FOUR BASIC COMPUTER FUNCTIONS

FIGURE 15-1 All computer systems perform four basic functions:input, processing, storage, and output.




• Input– A signal from a device

that can be as simple as a button or a switch on an instrument panel, or a sensor on an automotive engine.

FIGURE 15-2 A potentiometer uses a movable contact to vary resistance and send an analog signal.




• Processing– The term used to describe how input voltage signals

received by a computer are handled through a series of electronic logic circuits maintained in its programmed instructions.




• Storage– The place where the program instructions for a computer

are stored in electronic memory.




• Output– After the computer has processed the input signals, it

sends voltage signals or commands to other devices in the system,



DIGITAL COMPUTERS

• The digital computer can process thousands of digital signals per second because its circuits are able to switch voltage signals on and off in billionths of a second.

• The voltage signal or processing function is a simple high-low, yes-no, on-off signal.

FIGURE 15-3 Many electronic components are used to construct a typical vehicle computer. Notice all of the chips, resistors, and capacitors that are used in this General Motors computer.



DIGITAL COMPUTERSParts of a Computer• Central Processing Unit (CPU)

– The CPU can be considered the heart of a computer because it performs the essential mathematical operations and logic decisions that make up its processing function.

• Computer Memory– Other IC devices store the computer operating program, system

sensor input data, and system actuator output data information that is necessary for CPU operation.



DIGITAL COMPUTERSComputer Programs

FIGURE 15-4 This typical ignition timing map was developed from testing and used by the vehicle computer to provide the optimum ignition timing for all engine speeds and load combinations.

FIGURE 15-5 A replaceable PROM used in a General Motors computer.Notice that the sealed access panel has been removed to gain access.



DIGITAL COMPUTERSClock Rates and Timing• The microprocessor

communicates by transmitting long strings of 0s and 1s in a language called binary code

FIGURE 15-6 The clock generator produces a series of pulses that are used by the microprocessor and other components to stay in step with each other at a steady rate.



DIGITAL COMPUTERSComputer Speeds• The speed at which a computer operates is specified by the

cycle time, or clock speed, required to perform certain measurements.



DIGITAL COMPUTERSBaud Rate• The computer transmits bits of a serial data stream

at precise intervals.• The computer speed is called the baud rate, or bits

per second.



DIGITAL COMPUTERSControl Module Locations• The onboard automotive computer maybe called an

electronic control unit (ECU), electronic control module (ECM), electronic control assembly(ECA), or a controller, depending on the manufacturer and the computer application.



DIGITAL COMPUTERSControl Module Locations

FIGURE 15-7 This powertrain control module (PCM) is located under the hood on this Chevrolet pickup truck.

FIGURE 15-8 This PCM on a DaimlerChrysler vehicle can only be seen by hoisting the vehicle. It is located next to the radiator and in the airflow to help keep it cool.



COMPUTER INPUT SENSORSEngine speed (RPM) sensor.• Thissignalcomesfromtheprimarysignalinthe

ignitionmodule.



COMPUTER INPUT SENSORS MAP (manifold absolute pressure) sensor.• This sensor detects engine load. • The computer uses this information for fuel delivery and for

onboard diagnosis of other sensors and systems such as the exhaust gas recirculation(EGR) system.



COMPUTER INPUT SENSORSMAF (mass airflow) sensor.• This sensor measures the mass (weight and density) of the

air entering the engine.• The computer uses this information to determine the amount

of fuel needed by the engine.



COMPUTER INPUT SENSORSECT (engine coolant temperature) sensor.• This sensor measures the temperature of the engine coolant

needed by the computer to determine the amount of fuel and spark advance.

• This is a major sensor, especially when the engine is cold and when the engine is first started.



COMPUTER INPUT SENSORSO2S (oxygen sensor)• This sensor measures the oxygen in the exhaust stream. • These sensors are used for fuel control and to check other

sensors and systems.



COMPUTER INPUT SENSORSTP (throttle position) sensor.• This sensor measures the throttle opening and is used by

the computer to control fuel delivery as well as spark advance and the shift points of the automotive transmission/transaxle.



COMPUTER INPUT SENSORSVS (vehicle speed) sensor• This sensor measures the vehicle speed using a

sensor located at the output of the transmission/transaxle or by monitoring sensors at the wheel speed sensors.



COMPUTER OUTPUTS

• A vehicle computer can do only two things. – Turn a device on. – Turn a device off.



COMPUTER OUTPUTS

• Fuel injectors. • Ignition timing. • Transmission shifting. • Idle speed control. • Evaporative emission control solenoids.



FUEL CONTROL SYSTEM OPERATING MODES• A computer-controlled fuel metering system can be selective.• Control logic programmed into the computer determines the

choice of operating mode according to engine operating conditions.



SUMMARY

1. The Society of Automotive Engineers (SAE) standardJ-1930 specifies that the term power train control module(PCM) be used for the computer that controls the engine and transmission in a vehicle.

2. The four basic computer functions are input, processing,storage, and output.

3. Read-only memory (ROM) can be programmable (PROM),erasable (EPROM), or electrically erasable (EEPROM).

4. Computer input sensors include engine speed (RPM),MAP, MAF, ECT, O2S, TP, and VS.

5. A computer can only turn a device on or turn a device off,but it can do either operation rapidly.



REVIEW QUESTIONS

1. What part of the vehicle computer is considered to be the brain?

2. What is the difference between volatile and nonvolatile RAM?

3. List four input sensors.4. List four output devices.



CHAPTER QUIZ

1. What unit of electricity is used as a signal for a computer?

a) Voltb) Ohmc) Ampered) Watt



CHAPTER QUIZ

1. What unit of electricity is used as a signal for a computer?

a) Voltb) Ohmc) Ampered) Watt



CHAPTER QUIZ

2. The four basic computer functions include _____.a) Writing, processing, printing, and rememberingb) Input, processing, storage, and outputc) Data gathering, processing, output, and

evaluationd) Sensing, calculating, actuating, and processing



CHAPTER QUIZ

2. The four basic computer functions include _____.a) Writing, processing, printing, and rememberingb) Input, processing, storage, and outputc) Data gathering, processing, output, and

evaluationd) Sensing, calculating, actuating, and processing



CHAPTER QUIZ

3. All OBD-II vehicles use what type of read-only memory?

a) ROMb) PROMc) EPROMd) EEPROM



CHAPTER QUIZ

3. All OBD-II vehicles use what type of read-only memory?

a) ROMb) PROMc) EPROMd) EEPROM



CHAPTER QUIZ

4. The brain of the computer is the _____.a) PROMb) RAMc) CPUd) AD converter



CHAPTER QUIZ

4. The brain of the computer is the _____.a) PROMb) RAMc) CPUd) AD converter



CHAPTER QUIZ

5. Computer speed is measured in _____.a) Baud rateb) Clock speed (Hz)c) Voltaged) Bytes



CHAPTER QUIZ

5. Computer speed is measured in _____.a) Baud rateb) Clock speed (Hz)c) Voltaged) Bytes



CHAPTER QUIZ

6. Which item is a computer input sensor?a) RPMb) Throttle position anglec) Engine coolant temperatured) All of the above



CHAPTER QUIZ

6. Which item is a computer input sensor?a) RPMb) Throttle position anglec) Engine coolant temperatured) All of the above



CHAPTER QUIZ

7. Which item is a computer output device?a) Fuel injector b) Transmission shift solenoidc) Evaporative emission control solenoidd) All of the above



CHAPTER QUIZ

7. Which item is a computer output device?a) Fuel injector b) Transmission shift solenoidc) Evaporative emission control solenoidd) All of the above



CHAPTER QUIZ

8. The SAE term for the vehicle computer is _____.a) PCM b) ECMc) ECAd) Controller



CHAPTER QUIZ

8. The SAE term for the vehicle computer is _____.a) PCM b) ECMc) ECAd) Controller



CHAPTER QUIZ

9. What two things can a vehicle computer actually perform (output)?

a) Store and process informationb) Turn something on or turn something offc) Calculate and vary temperatured) Control fuel and timing only



CHAPTER QUIZ

9. What two things can a vehicle computer actually perform (output)?

a) Store and process informationb) Turn something on or turn something offc) Calculate and vary temperatured) Control fuel and timing only



CHAPTER QUIZ

10. Analog signals from sensors are changed to digital signals for processing by the computer through which type of circuit?

a) Digitalb) Analogc) AD converterd) PROM



CHAPTER QUIZ

10. Analog signals from sensors are changed to digital signals for processing by the computer through which type of circuit?

a) Digitalb) Analogc) AD converterd) PROM



END

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