Ignition System: Description and Operation

PURPOSE
To provide a means for the Powertrain Control Module (PCM) to control the supply of a "timed" secondary voltage spark. The secondary voltage spark is carried to each cylinder for the purpose of igniting the air/fuel charge in any given cylinder at the optimum moment.

OPERATION

NOTE: The CAMSHAFT POSITION SIGNAL used in the ignition system is not related to the component Camshaft Position Sensor. The component Camshaft Position Sensor is used for fuel injection timing purposes and should not be confused with the ignition system signal "CAMSHAFT POSITION SIGNAL".

- The Ignition Control Module receives the Crankshaft Position Signal from the Crankshaft Position Sensor (CKP).
- The Ignition Control Module converts the CKP signal into a "CAMSHAFT POSITION SIGNAL".
- The PCM uses the CAMSHAFT POSITION SIGNAL to detect when the No.1 cyl. is at Top Dead Center.
- The PCM uses a programed spark advance map to process the CAMSHAFT POSITION SIGNAL along with other system inputs to produce a Spark Output (SPOUT) signal.
- The Ignition Control Module uses the SPOUT and CKP input signals to control the ignition spark timing by switching the primary circuits of the ignition coils On and Off.
- The Ignition Control Module also sends an Ignition Diagnostic Monitor Signal back to the PCM. This is used as a tachometer output signal and also allows the PCM to detect when the Ignition Control Module is operating in "Fail Safe Mode" due to an ignition system failure.
- The Fail Safe Mode feature in the Ignition Control Module allows continued vehicle operation during some ignition system malfunctions.
- The Ignition Control Module will produce a fixed spark timing output of 10° BTDC if it does not receive a SPOUT signal from the PCM. If the Ignition Control Module does not receive an input signal from the Crankshaft Position Sensor the engine will not start.