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OBJECTIVES
After studying Chapter 11, the reader will be able to:
1. Prepare for ASE Electrical/Electronic Systems (A6)
certification test content area “A” (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).
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
COMPUTER CONTROL
• Modern automotive control systems consist of a
network of electronic sensors, actuators, and
computer modules designed to regulate the
powertrain and vehicle support systems.
• The powertrain control module (PCM) is the heart
of this system.
– It coordinates engine and transmission operation,
processes data, maintains communications, and makes
the control decisions needed to keep the vehicle
operating.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THE FOUR BASIC COMPUTER FUNCTIONS
• The operation of every computer can be divided into four
basic functions.
–
–
–
–
Input
Processing
Storage
Output
FIGURE 11-1 All computer systems perform four basic
functions: input, processing, storage, and output.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THE FOUR BASIC COMPUTER FUNCTIONS
FIGURE 11-2 A potentiometer uses a movable contact to vary resistance and send
an analog voltage right to the PCM.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
DIGITAL COMPUTERS
• In a digital computer,
the voltage signal or
processing function is a
simple high/low, yes/no,
on/off signal.
• The digital signal
voltage is limited to two
voltage levels: high
voltage and low
voltage.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
FIGURE 11-3 Many electronic components are
used to construct a typical vehicle computer.
Notice the quantity of chips, resistors, and
capacitors used in this General Motors
computer.
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
DIGITAL COMPUTERS
Parts of a Computer
• The software consists of the programs and logic
functions stored in the computer’s circuitry.
• The hardware is the mechanical and electronic
parts of a computer.
– Central Processing Unit (CPU).
– Computer Memory.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
DIGITAL COMPUTERS
Computer Programs
• By operating a vehicle on a
dynamometer and manually
adjusting the variable
factors such as speed,
load, and spark timing, it is
possible to determine the
optimum output settings for
the best driveability,
economy, and emission
control.
• This is called engine
mapping.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
FIGURE 11-4 Typical ignition timing map
developed from testing and used by the
vehicle computer to provide the optimum
ignition timing for all engine speeds and
load combinations.
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
DIGITAL COMPUTERS
Computer Programs
FIGURE 11-5 A replaceable PROM used in a General Motors computer. Notice
that the sealed access panel has been removed to gain access.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
DIGITAL COMPUTERS
Clock Rates and Timing
• The microprocessor
receives sensor input
voltage signals, processes
them by using information
from other memory units,
and then sends voltage
signals to the appropriate
actuators.
FIGURE 11-6 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.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
DIGITAL COMPUTERS
Computer Speeds
• Not all computers operate at the same speed; some
are faster than others.
– The speed at which a computer operates is specified by
the cycle time, or clock speed, required to perform certain
measurements.
– Cycle time or clock speed is measured in megahertz (4.7
MHz, 8.0 MHz, 15 MHz, 18 MHz, etc.).
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
DIGITAL COMPUTERS
Baud Rate
• The computer transmits bits of a serial data stream
at precise intervals.
– The computer’s processing speed is called the baud rate,
or bits per second.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
DIGITAL COMPUTERS
Control Module Locations
• The onboard automotive
computer has many names.
• It may be 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.
FIGURE 11-7 This powertrain control
module (PCM) is located under the hood
on this Chevrolet pickup truck.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
DIGITAL COMPUTERS
Control Module Locations
FIGURE 11-8 This PCM
on a Chrysler vehicle can
only be seen by hoisting
the vehicle because it is
located next to the
radiator, and in the airflow
to help keep it cool.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
COMPUTER INPUT SENSORS
• The vehicle computer uses the signals (voltage
levels) from the following engine sensors:
– Engine speed (RPM or revolutions per minute)
sensor.
– MAP (manifold absolute pressure) sensor.
– MAF (mass airflow) sensor.
– ECT (engine coolant temperature) sensor.
– O2S (oxygen sensor).
– TP (throttle position) sensor.
– VS (vehicle speed) sensor.
– Knock sensor.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
COMPUTER OUTPUTS
• A vehicle computer can do just two things.
– Turn a device on.
– Turn a device off.
• Typical output devices include the following.
–
–
–
–
–
Fuel injectors.
Ignition timing.
Transmission shifting.
Idle speed control.
Evaporative emission control solenoids.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
FUEL CONTROL SYSTEM OPERATING MODES
• A computer-controlled fuel metering system can be selective.
• Depending on the computer program, it may have different
operating modes.
• The onboard computer does not have to respond to data
from all of its sensors, nor does it have to respond to the
data in the same way each time.
• Under specified conditions, it may ignore sensor input.
– Or, it may respond in different ways to the same input signal, based
on inputs from other sensors.
• Most current control systems have two operating modes:
open and closed loop.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
SUMMARY
1. The Society of Automotive Engineers (SAE) standard J1930 specifies that the term powertrain control module
(PCM) be used for the computer that controls the engine
and transmission in a vehicle.
2. The four basic computer functions include 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 the operation very rapidly.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
REVIEW QUETSIONS
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.
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
1. What unit of electricity is used as a signal for a
computer?
a)
b)
c)
d)
Volt
Ohm
Ampere
Watt
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
1. What unit of electricity is used as a signal for a
computer?
a)
b)
c)
d)
Volt
Ohm
Ampere
Watt
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
2. The four basic computer functions include _____.
a)
b)
c)
d)
Writing, processing, printing, and remembering
Input, processing, storage, and output
Data gathering, processing, output, and evaluation
Sensing, calculating, actuating, and processing
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
2. The four basic computer functions include _____.
a)
b)
c)
d)
Writing, processing, printing, and remembering
Input, processing, storage, and output
Data gathering, processing, output, and evaluation
Sensing, calculating, actuating, and processing
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
3. All OBD II vehicles use what type of read-only
memory?
a)
b)
c)
d)
ROM
PROM
EPROM
EEPROM
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
3. All OBD II vehicles use what type of read-only
memory?
a)
b)
c)
d)
ROM
PROM
EPROM
EEPROM
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
4. The “brain” of the computer is the _____.
a)
b)
c)
d)
PROM
RAM
CPU
AD converter
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
4. The “brain” of the computer is the _____.
a)
b)
c)
d)
PROM
RAM
CPU
AD converter
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
5. Computer processing speed is measured in
_____.
a)
b)
c)
d)
Baud rate
Clock speed (Hz)
Voltage
Bytes
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
5. Computer processing speed is measured in
_____.
a)
b)
c)
d)
Baud rate
Clock speed (Hz)
Voltage
Bytes
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
6. Which item is a computer input sensor?
a)
b)
c)
d)
RPM
Throttle position angle
Engine coolant temperature
All of the above
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
6. Which item is a computer input sensor?
a)
b)
c)
d)
RPM
Throttle position angle
Engine coolant temperature
All of the above
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
7. Which item is a computer output device?
a)
b)
c)
d)
Fuel injector
Transmission shift solenoid
Evaporative emission control solenoid
All of the above
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
7. Which item is a computer output device?
a)
b)
c)
d)
Fuel injector
Transmission shift solenoid
Evaporative emission control solenoid
All of the above
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
8. The SAE term for the vehicle computer is _____.
a)
b)
c)
d)
PCM
ECM
ECA
Controller
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
8. The SAE term for the vehicle computer is _____.
a)
b)
c)
d)
PCM
ECM
ECA
Controller
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
9. What two things can a vehicle computer actually
perform (output)?
a)
b)
c)
d)
Store and process information
Turn something on or turn something off
Calculate and vary temperature
Control fuel and timing only
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
9. What two things can a vehicle computer actually
perform (output)?
a)
b)
c)
d)
Store and process information
Turn something on or turn something off
Calculate and vary temperature
Control fuel and timing only
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
10. Analog signals from sensors are changed to digital
signals for processing by the computer through
which type of circuit?
a)
b)
c)
d)
Digital
Analog
AD converter
PROM
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
10. Analog signals from sensors are changed to digital
signals for processing by the computer through
which type of circuit?
a)
b)
c)
d)
Digital
Analog
AD converter
PROM
Automotive Fuel and Emissions Control Systems, 2/e
By James D. Halderman and Jim Linder
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458