Modes of Operation

DESCRIPTION
Anytime the PCM does not apply 5 volts to the ignition control module bypass circuit, the ignition control module controls ignition by triggering each of the three coils in the proper sequence at a pre-determined dwell. This is called Bypass Mode ignition.

OPERATION
When the PCM begins receiving 18X reference and 3X reference pulses, the PCM applies 5 volts to the ignition control module bypass circuit. This signals the ignition control module to allow the PCM to control the dwell and spark timing. This is IC Mode ignition. During IC Mode, the PCM compensates for all driving conditions.

In the IC Mode, the ignition spark timing and ignition dwell time is fully controlled by the PCM. The ignition control module is responsible for proper ignition coil sequencing during both Bypass Mode and IC Mode. IC spark advance and ignition dwell is calculated by the PCM using the following inputs:

^ Engine speed (18X reference or 3X reference).
^ Crankshaft position (18X reference or 3X reference and camshaft position PCM input signal).
^ Engine coolant temperature (ECT sensor).
^ Throttle position (TP sensor).
^ Knock signal (Knock sensor).
^ Park/Neutral Position (trans range switch or park/neutral position switch).
^ Vehicle speed (Vehicle Speed Sensor / Trans Output Speed Sensor).
^ PCM and ignition system supply voltage (PCM ignition feed voltage).

Once the change is made to IC Mode, it will stay 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.


DIAGNOSIS
If the 18X reference signal is not received by the PCM while the engine is running, a DTC P0336 will be set and 3X reference will be used to control spark advance under 1200 RPM, and Bypass Mode will be in effect at under 400 RPM. The engine will continue to run and start normally.

If the 3X reference signal is not received by the PCM while the engine is running, the PCM will use the 18X reference pulses to calculate RPM and crankshaft position. The engine will continue to run and start normally, but DTC P1374 will be set. Poor engine performance and possibly a MIL with no DTC can be caused if the Reference Low circuit is open or connected to ground at the PCM.

The IC output circuitry in the PCM generates IC output pulses anytime crankshaft reference signal input pulses are being received. When the ignition system is operating in the Bypass Mode (no voltage on the bypass control circuit), the ignition control module grounds the IC pulses coming from the PCM. The ignition control module will remove the ground from the IC circuit only after switching to the IC Mode. The PCM commands switching to IC Mode by applying 5 volts on the bypass circuit to the ignition control module. The PCM monitors the IC and Bypass circuits for electrical malfunctions affecting proper ignition system operation. If a malfunction occurs, diagnosis is included in DTC P1351, P1352, P1361 and P1362 diagnostic tables. If diagnostic trouble codes are encountered, go to the DTC tables for diagnosis.