Ignition Coil: Description and Operation

IGNITION CONTROL MODULE (ICM) AND IGNITION COILS

Each ignition coil is responsible for supplying secondary energy to a pair of spark plugs. The ignition control signals output by the PCM am amplified by the ICM in order to fire each coil. The spark events are triggered by the ICM, but the module has no influence on spark timing. The ICM is also responsible for detecting and supplying a Camshaft Position (CMP) signal pulse to the PCM to be used for sequential fuel injection. This ignition system does not use a conventional CMP sensor that detects valve train position. The ICM detects when either cylinder 1 or cylinder 3 has fired on the cylinders compression stroke using sensing circuitry integrated within each coil. The sensing circuit detects the polarity and the strength of the secondary voltage output, the higher output is always at the event cylinder. The ICM sends a CMP signal to the PCM based on the voltage difference between the event and waste cylinder firing energy. This system is called compression sense ignition. By monitoring the camshaft position and Crankshaft Position (CKP) signals the PCM can accurately time the operation of the fuel injectors.