Ignition System Modes of Operation

Anytime the PCM does not apply 5 volts to the IC timing signal circuit, the IC module controls ignition by triggering each coil in the proper sequence at a pre-determined dwell. This is called Bypass Mode ignition used during cranking and running below a certain RPM, or during a default mode due to a system failure.

When the PCM begins receiving 18x reference and 3X reference pulses, the PCM applies 5 volts to the IC timing signal circuit. This signals the IC 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 If the IC mode changes due to a system fault, the mode will stay in default until the ignition is cycled OFF to ON, or the fault is not present.