Ignition Control Module: Description and Operation

Operation:
The PCM supplies two signals to the electronic ignition module. One signal is an ignition timing waveform, and the other signal is a fail-safe discrete signal that informs the ignition module that the PCM is operational. The falling edge of the timing waveform indicates the beginning of the spark event. The timing waveform is a 0 to 5 volt variable duty-cycle, and frequency, based on the engine waveform and is generated by the PCM to indicate spark advance.

The discrete signal is a constant five volts while the PCM is operational and grounded when the PCM is not operational.