General Description

The PCM continuously sends out Ignition Control (IC) timing pulses to the Ignition Control Module (ICM) on the IC circuit. Anytime the PCM does not apply 5 volts to the ignition control module (ICM) bypass circuit, the ICM controls ignition timing. The ICM fires each of the three coils in the proper sequence at a fixed timing of 10° BTDC. This mode of operation is called the Bypass Mode.

When engine speed reaches a specific value and the PCM receives the calibrated number of 3X reference pulses, the PCM applies 5 volts to the ICM on the bypass circuit. This signals the ICM to transfer spark timing control to the PCM. This mode of operation is called the IC Mode. During the IC Mode, the PCM controls spark advance and dwell to compensate for a wide range of engine speeds and loads.

In the IC Mode, the PCM completely controls the IC spark timing. The ICM, in any mode, is always responsible for proper ignition coil sequencing. In the IC mode, the PCM calculates IC spark timing based upon input signals from the following:
^ The engine speed (18X reference or 3X reference).
^ The crankshaft position (18X reference or 3X reference and camshaft position PCM input signal).
^ The Engine Coolant Temperature (ECT sensor).
^ The Throttle Position (TP sensor).
^ The knock signals (knock sensors).
^ The park/neutral position (transaxle range switch or park/neutral position switch).
^ The vehicle speed (vehicle speed sensor / trans output speed sensor).
^ The PCM and the ignition system supply voltage (PCM ignition feed voltage).

Once the change is made to IC Mode, the change stays in effect until one of the following conditions occurs:
^ The engine is turned off.
^ The engine quits running.

If a PCM/IC fault (DTC P1351, P1352, P1361 and P1362) is detected while the engine is running, the engine may quit running. However the vehicle will restart, and may remain in Bypass Mode with a noticeable loss of performance.