Equus 3123 - GM Code Reader (1982 - 1995) User Manual

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1.1 YOUR VEHICLE'S COMPUTER SYSTEM

Today's vehicles are equipped with computer self-testing
abilities that can locate problems in your vehicle and store
them as service codes in the vehicle's onboard computer. The
Code Reader allows you access to the computer's memory and
recalls the service codes.

1.1.1 Instrument Panel Indicator Lights

Your vehicle's Instrument panel has several indicator lights, such
as the "Check Engine", "Service Engine Soon", "ABS", "Shift to
D2" and "Temperature" indicator lights. These lights do more
than tell you to check for engine, brake, or other component
malfunctions. They can also transmit the service codes in the
computer memory by blinking on and off.

NOTE:

If your instrument panel indicator lights do not come
on when you turn on the ignition, please refer to your
vehicle's service manual. You may have problems in
the car's circuitry. You must fix these problems before
you can obtain service codes from the vehicle's
onboard computer.

1.1.2 Service Codes

The service codes are also called "fault codes", "diagnostic
codes" or "trouble codes". These codes can be used to identify
systems or components which are malfunctioning.

The computer records codes for two types of problems:

■

"Hard" Codes. "Hard" codes are stored for problems
which are happening now. The instrument panel indicator
light will stay on when the engine is running.

■

"Intermittent" Codes or "Continuous Memory" Codes.
Intermittent service codes are stored in the computer's
memory for problems which occur intermittently, or for
problems which happened in the past but are not currently
present. Intermittent problems may cause the panel
indicator light to flicker or to turn on intermittently.
Intermittent codes are stored in the computer's memory for
a set period of time (usually 50 start cycles). If an
intermittent problem does not recur within this time
period, the computer automatically erases the related
intermittent fault code from it's memory.

CHECK ENGINE

SERVICE

ENGINE

SOON