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The On-Line Help screen shown above
has a
in the last column. To view the next
On-Line Help screen, press the DOWN
arrow key. That screen is shown below:
Notice now that both arrow symbols (
are visible in the last column of the display.
This indicates that you can either page up
to a previous On-Line Help screen, or
page down to the next On-Line Help
screen by using the UP and DOWN arrow
keys. The previous On-Line Help screen
is always the one you just viewed, just as
with Function Lists.
Another symbol on the screen you might
have noticed is the bell (
) symbol in the
lower right-hand corner as shown below:
This bell symbol indicates that the sound
alert is on or active. Each time you press
a key, you should hear a beep. If you do not
see this symbol, then the keys should
remain silent when pressed. Information
on changing this setting is found in section
1-7: Scan Tool Setup.
1-7: ScanTool Setup
Tool Setup is used to change the scan
tool's default sound and measurement
unit settings. To change the scan tool's
default settings, select the Tool Setup
option from the Function List (NOTE: This
is a GM Function List – Function Lists for
other manufacturers may differ slightly.):
)
After selecting the Tool Setup option, you
are given the choice to change either the
ScanTool's measurement units or whether
the beeper will be On or Off. If the bell (
symbol appears in the lower right hand
corner of the display, then the beeper is
turned On.
Depending on whether you select English/
Metric or Beeper On/Off, the ScanTool will
display one of the following screens:
When the beeper sound is turned Off, the
bell (
) symbol will no longer appear on
the lower right hand corner of the display.
NOTE: If you change the Beeper and
Measurement Units to a setting other than
the default, then all changes will revert
back to the default settings the next time
the scan tool is used.
12
Section 2: Vehicle Computer Basics
2-1 Basics of Computer-Controlled Cars
This section explains the engine com-
puter control system, the types of sensors
and how the computer controls engine
fuel delivery, idle speed and timing. Addi-
tional information may be found in techni-
cal support books at your local library or
auto parts store. The more you know about
the computer system, the better you can
diagnose vehicle computer problems.
Computer controls were originally in-
stalled on vehicles to meet federal gov-
ernment regulations for lower emissions
)
levels and improved fuel economy. This
began in the early 1980's when basic
mechanical systems were no longer able
to accurately control key engine param-
eters. A computer could be programmed
to control the engine under various oper-
ating conditions, making the engine more
reliable. While these early systems were
very limited in the scope of their control,
providing only 10-14 trouble codes, they
did help guide the vehicle repair process.
Today, computer controls have made cars
and trucks faster, cleaner, and more effi-
cient than ever before. In fact, without the
government mandates for fuel efficiency
and emissions control, cars and trucks
today would not be nearly as powerful,
reliable, and comfortable as they are.
What the computer controls:
The main control areas of the vehicle
computer are fuel delivery, idle speed,
spark advance, and emissions controls.
Some on-board computers may also con-
trol the transmission, brakes, and suspen-
sion systems as well.
What has not changed?
A computer-controlled engine is very simi-
lar to the older, non-computerized en-
gine. It is still an internal combustion en-
gine with pistons, spark plugs, valves, and
camshaft(s). The ignition, charging, start-
ing, and exhaust systems are very similar
as well. You test and repair these systems
just as before. The technical manuals for
these components show you how to per-
form the tests. Additionally, compression
gauges, vacuum pumps, dwell/tach
meters, engine analyzers, and timing
lights will continue to be used.
The Engine Computer Control system
The vehicle's on-board computer, or
Powertrain Control Module (PCM), is the
"heart" of the system. It is sealed in a metal
box and connected to the rest of the en-
gine by a main wiring harness. The PCM
is located, in most cases, in the passenger
compartment, behind the dashboard or in
the "kick panel" position, although some
manufacturers locate the computer con-
trol module in the engine compartment
area. Most PCMs can withstand a lot of
vibration and are built to live in a rugged
environment.
The PCM is permanently programmed by
the factory engineers. The program is a
complex list of look-up tables and instruc-
tions telling the computer how to control
the engine based on various driving con-
ditions. To do its job, the computer uses
sensors to know what is happening and
then provide instructions back to a net-
work of switches and actuators through-
out the vehicle.
Sensors, switches, and actuators give
the computer information
Sensors are devices which measure op-
erating conditions and translate them into
signals the computer can understand.
13
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