Electronic Ignition System Diagnosis: Description

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This ignition system uses one coil for each pair of cylinders, mounted to the Ignition Control Module (ICM). Companion cylinders are a pair of cylinders that are at Top Dead Center (TDC) at the same time. The cylinder that is at TDC of the compression stroke is called the event cylinder. The cylinder that is at TDC of the exhaust stroke is called the waste cylinder. When the coil is triggered both companion cylinder spark plugs fire at the same time, completing a series circuit.

The ICM has independent power and ground circuits. The circuits between the ICM and the Powertrain Control Module (PCM) consists of the following circuits:

The Ignition Control (IC) timing signal.
The IC timing control.
The low resolution engine speed signal.
The medium resolution engine signal.
The camshaft position signal.
The low reference.

The ICM sends 3X signals to the PCM, and controls the timing advance during engine cranking. The timing advance changes to PCM control after the following actions occur:

The PCM receives the second 3X signal.
The PCM applies 5 volts to the Ignition Control (IC) timing signal circuit.

The ICM monitors the CKP sync signal when the engine is cranking. The CKP sync signal is passed from the CKP sensor to the ICM on the CKP sensor 2 signal circuit. The CKP sync signal is used to determine the correct cylinder pair and initiate the ignition coil firing sequence. The 18X reference pulses are passed from the CKP sensor to the ICM on the CKP sensor 1 circuit. The 18X reference pulses are used for fuel injection and ignition control. After the ICM receives both signals, the ICM passes the 18X and 3X reference signals to the PCM. The CMP and the CKP sensors share a 12 volt reference and low reference circuit. The CKP sensor consists of the following circuits:

A 12 volt reference.
A low reference.
A CKP sensor 1 signal.
A CKP sensor 2 signal.