Ignition Circuit Faults

An open or ground in the Ignition Control (IC) circuit will result in the engine continuing to run, but in a backup ignition timing mode (module timing) at a calculated timing value and the Malfunction Indicator Lamp (MIL) "Service Engine Soon" will not be "ON."

The PCM uses information from the MAP and engine Coolant Temperature (ECT) sensors in addition to RPM to calculate spark advance as follows:

^ 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. Related Tests, Information and Procedures