S10/T10 P/U 2WD L4-2.2L VIN 4 (1995)
Ignition Control Module: Testing and Inspection
SYMPTOM DIAGNOSIS
An open or ground in the Ignition Control (IC) circuit will result in the engine continuing to run, but in a back-up ignition timing mode (module
tilting) at a calculated timing value and the Malfunction Indicator Lamp (MIL) Service Engine Soon will not be "ON." If the IC fault is still
present the next time the engine is restarted, a Diagnostic Trouble Code (DTC) 42 will be set and the engine will operate in Ignition Control
Module (ICM) timing mode. This may cause poor performance and reduced fuel economy.
An open or grounded bypass circuit will set a Diagnostic Trouble Code (DTC) 42 and result in the engine operating in a back-up ignition timing
mode (module timing) at a calculated timing value. This may cause poor performance and reduced fuel economy.
The PCM uses information from the Manifold Absolute Pressure (MAP) and Engine Coolant Temperature (ECT) sensors in addition to RPM to
calculate spark advance as follows:
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Low MAP output voltage = More spark advance.
^
Cold engine = More spark advance.
^
High MAP output voltage = Less spark advance.
^
Hot engine = Less spark advance.
Therefore, detonation could be caused by low MAP output or high resistance in the coolant sensor circuit.
Poor performance could be caused by high MAP output or low resistance in the coolant sensor circuit.
If the ENGINE cranks but will not run or immediately stalls, CHART A-3 must be used to determine if the failure is in the Electronic Ignition (El)
system or the fuel system. See: Computers and Control Systems/Testing and Inspection
Diagnostic Trouble Code (DTC) 42
If DTC 42 is set, that chart must he used for diagnosis. If the symptom is "Engine Misses" and the ignition system is suspected, use Misfire At
Idle and Misfire Under Load. Refer to Diagnosis by Symptom. See: Computers and Control Systems/Testing and Inspection
