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OBJECTIVES
After studying Chapter 2, 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).
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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 2-1 All computer systems perform four basic
functions: input, processing, storage, and output.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THE FOUR BASIC COMPUTER FUNCTIONS
FIGURE 2-2 A potentiometer uses a movable contact to vary resistance and send
an analog voltage right to the PCM.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THE FOUR BASIC COMPUTER FUNCTIONS
FIGURE 2-3 A replaceable PROM used in an older General
Motors computer. Notice that the sealed access panel has
been removed to gain access.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THE FOUR BASIC COMPUTER FUNCTIONS
Low-Side Drivers
• Low-side drivers, often abbreviated LSD, are transistors
that complete the ground path in the circuit.
FIGURE 2-4 A typical output driver. In this case, the PCM applies voltage
to the fuel pump relay coil to energize the fuel pump.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THE FOUR BASIC COMPUTER FUNCTIONS
Low-Side Drivers
FIGURE 2-5 A typical lowside driver (LSD) which uses
a control module to control
the ground side of the relay
coil.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THE FOUR BASIC COMPUTER FUNCTIONS
High-Side Drivers
• High-side drivers, often
abbreviated HSD, control
the power side of the
circuit.
FIGURE 2-6 A typical module controlled highside driver (HSD) where the module itself
supplies the electrical power to the device.
The logic circuit inside the module can detect
circuit faults including continuity of the circuit
and if there is a short-to-ground in the circuit
being controlled.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THE FOUR BASIC COMPUTER FUNCTIONS
Pulse Width Modulation
• Pulse width modulation
(PWM) is a method of
controlling an output using
a digital signal.
• Instead of just turning
devices on or off, the
computer can control
output devices more
precisely by using pulse
width modulation.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
FIGURE 2-7 Both the top and bottom pattern
have the same frequency. However, the amount
of on-time varies. Duty cycle is the percentage
of the time during a cycle that the signal is
turned on.
© 2009 Pearson Higher Education, Inc.
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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.
• Since there is no stepped
range of voltage or current
in between, a digital binary
signal is a “square wave.”
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
FIGURE 2-8 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.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
FIGURE 2-9 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 2-10 The calibration module on many
Ford computers contains a system PROM.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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 2-11 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.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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.).
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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 2-12 This powertrain control
module (PCM) is located under the hood
on this Chevrolet pickup truck.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
DIGITAL COMPUTERS
Control Module Locations
FIGURE 2-13 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.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
MODULE COMMUNICATION AND NETWORKS
Serial Data
– Serial data is data that is transmitted by a series of
rapidly changing voltage signals pulsed from low to high
or from high to low.
Multiplexing
– Multiplexing is the process of sending multiple signals of
information at the same time over a signal wire and then
separating the signals at the receiving end.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
MODULE COMMUNICATION AND NETWORKS
FIGURE 2-14 A network
allows all modules to
communicate with other
modules.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
MODULE COMMUNICATION AND NETWORKS
• The three most common types of networks used on
General Motors vehicles include:
– Ring link networks
– Star link
– Ring/star hybrid
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
MODULE COMMUNICATION AND NETWORKS
FIGURE 2-15 A ring link network reduces the number of wires it takes
to interconnect all of the modules.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
MODULE COMMUNICATION AND NETWORKS
FIGURE 2-16 A star-link-type network where all of the modules are
connected together using splice packs.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
SAE COMMUNICATION CLASSIFICATIONS
• The Society of Automotive Engineers (SAE)
standards include three categories of in-vehicle
network communications, including the following.
– Class A
– Class B
– Class C
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
SAE COMMUNICATION CLASSIFICATIONS
FIGURE 2-17 A typical bus
system showing module CAN
communications and twisted
pairs of wire.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
MODULE COMMUNICATION DIAGNOSIS
• Most vehicle manufacturers specify that a scan tool
be used to diagnose modules and module
communications.
• Always follow the recommended testing
procedures, which usually require the use of a
factory scan tool.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
MODULE COMMUNICATION DIAGNOSIS
FIGURE 2-18 Checking
the terminating resistors
using an ohmmeter at the
DLC.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OBD II DATA LINK CONNECTOR
FIGURE 2-19 Sixteen-pin OBD II DLC with terminals identified. Scan tools use the
power pin (16) ground pin (4) for power so that a separate cigarette lighter plug is
not necessary on OBD II vehicles.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 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
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458