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When the SCAN Tool is connected to the Diagnostic
Connector with the key switch ON and the engine
OFF, the system will enter the Diagnostic Mode.
1. Display a DTC 12 by flashing the Malfunction Indicator
Lamp (indicating the system is operating
correctly).
2. Display any additional stored DTCs by flashing
the Malfunction Indicator lamp. Each DTC will
flash 3 times, then DTC 12 will flash again.
3. The Idle Air Control (IAC) valvemoves to its fully
extended position, blocking the idle air passage.
Field Service Mode
NOTE: The ignition timing can be set with a timing
light.
If the SCAN Tool is connected to the Diagnostic Connector
and turned ON with the engine running, system
will enter Field Service Mode. For the GM 3.0L
engine, this will cause the engine to run at approximately
1500 rpm and 8 before top dead center spark
advance. For GM 4.3L engine, the numbers are approximately
1000 rpm and 0 before top dead center
spark advance. While the system is in Field Service
Mode, new trouble codes can be kept in the ECM.
ECM Learning Ability
The ECM has a learning ability that lets it make corrections
for variations in the idle system to improve
idle performance. If the battery is disconnected for
any reason, the learning process resets and begins
again. To teach the vehicle, make sure that the engine
is at operating temperature. Drive the lift truck
at part throttle, with moderate acceleration, and idle
until normal performance returns.