MALFUNCTION INDICATOR LAMP (MIL)
Most engine control system related problems that affect
emissions or driveability of the vehicle will set
a diagnostic trouble code (DTC) and illuminate the
malfunction indicator lamp.
The MIL has the following functions:
1. It notifies the driver of a problem with the fuel
system, ignition system, or emission control system
so the driver can arrange for service as soon
as possible.
2. It will display DTCs that have been stored due to
a system malfunction.
The lamp should come on when the key is in the ON
position and the engine is not running. This feature
verifies that the lamp is in proper working order.
If the lamp does not come on with the vehicle key
ON/engine OFF, repair it as soon as possible. Once
the engine is in start or run mode, the lamp should
go off. If the lamp illuminates while the engine is in
the start or run mode, there is a current diagnostic
trouble code.
SPECTRUM DIAGNOSTIC TROUBLE
CODES (DTC)
Diagnostic trouble codes are set when the Spectrum
electronic control module (ECM) runs a diagnostic
self-test and the test fails. When a DTC is set, the
ECM will illuminate the malfunction indicator lamp
(MIL) on the instrument panel and save the code in
memory. The ECM will continue to run the self-test
unless the DTC is an oxygen sensor lean, oxygen sensor
rich, or an internal ECM related DTC. If the system
continues to fail the test, the lamp will stay illuminated
and the DTC is current (ACTIVE). All DTCs
are stored as historical faults until they are cleared.
All DTCs except the ECM related DTCs will automatically
clear from memory if the DTC does not reset
within 100 consecutive engine run cycles.
While a diagnostic trouble code is current for a sensor,
the ECMmay assign a default "limp home" value
and use that value in its control algorithms. All of the
system diagnostic self-tests run continuously during
normal vehicle operation.
The diagnostic trouble codes can be read by using either
the MIL lamp or a laptop computer. Refer to
Using a Laptop Computer to Diagnose the Spectrum
System and Using a Diagnostic Jumper to Diagnose
the ECI System, located in this section. Diagnostic
trouble codes can be cleared from memory with a laptop
computer or by turning the ignition key to the
OFF position and removing the system main power
fuse (F3) for 15 seconds.
If more than one DTC is detected, always begin with
the lowest number DTC and diagnose each problem
to correction unless directed to do otherwise by the
fault chart. The DTCs are numbered in order of importance.
Having DTC 112 and DTC 122, both concerning
the oxygen sensor, is possible. By repairing
DTC 112 first, the problem causing the DTC 122 may
also be corrected.
USING A LAPTOP COMPUTER TO
DIAGNOSE THE SPECTRUM SYSTEM
Tools Required Part Number
Laptop Computer N/A
Diagnostic Software 2067944
Spectrum Special
Tools Kit
2067935
A laptop computer is the preferred tool for performing
diagnostic testing of the Spectrum system. A laptop
computer, with the system diagnostic cable and
diagnostic software, is used to read and clear Diagnostic
Trouble codes. It is also used to monitor sensor
and actuator values. The diagnostic software also
performs several special tests.