Theory Of Operation

The Powertrain Control Modules (PCM-1 and PCM-2) do not directly control energizing the Ignition Coils. The Ignition Control Module (ICM) is used for direct control and diagnostics of the ignition system. The operation of the Ignition Coils occurs as follows: 

1. PCM-1 and PCM-2 send command signals to the ICM for Ignition Coil control.
2. The ICM replicates the commands to the Ignition Coils over the Coil Control circuits.
3. The ICM monitors the secondary circuit current and ionization of the coils over the Ionization Signal circuits (secondary signal feedback).
   NOTE:

   The Crank Position Sensor (CKP) is hard wired to PCM-1. The ICM and PCM-2 acquire the CKP Signal from PCM-1 on a dedicated hard wired circuit.

Each PCM performs diagnostics on the command signals to the ICM. The ICM performs diagnostics on the Ionization Signal circuits and Coil Control circuits. The ICM also uses the Ionization Signal feedback for monitoring for misfire events. The ICM reports the faults to PCM-1 and PCM-2. Each PCM records and stores the faults for the ignition system.

The PCM-1, PCM-2, and ICM communicate with each other over the Private Engine CAN bus circuit. The ICM communicates faults back to each PCM over the Private Engine CAN bus. There is also a Pulse Width Modulated (PWM) Liveness Signal circuit that is connected between the ICM and PCM-2. The Liveness Signal is used for backup communication in the case of a loss of communication over the Private Engine CAN bus. The Liveness Signal typically has a 10ms pulse width. In the case of a loss of Fused ASD Relay output to the Ignition Coils on either bank, the Liveness signal is set to a 20ms pulse width in order to communicate the Ignition Coil Supply Fuse failure as quickly as possible to the PCM.