Cavalier L4-2.2L VIN 4 (1998)
Ignition Control Module: Description and Operation
This system uses the same circuits between the ICM and the PCM that distributor type systems use. Following is a brief description for each of the IC
circuits.
Crankshaft Position (CKP) Sensor Activity (7X reference) - The CKP sensor generates a signal to the ICM which results in a reference pulse (square
wave signal) being sent to the PCM. The PCM uses this signal to calculate crankshaft position, engine speed and injector pulse width. The engine will
not start or run if this circuit is open or grounded.
Reference Low - This wire is grounded through the ICM and insures that the ground circuit has no voltage drop between the ICM and the PCM which
could affect performance. The PCM compares voltage pulses on the 7X or reference input to those on this circuit, ignoring any pulses that appear on
both. A pulse that appears on the reference low circuit alone is assumed to be caused by Radio Frequency Interference (RFI).
Ignition Control (IC) 1 & 2 - The PCM sends the ignition control pulse to the ICM on these circuits. These signals are similar to the 7X reference pulse
square wave except that the PCM uses sensor inputs to determine the pulse timing to control spark advance. When the PCM receives the 7X signal, it
will determine which pair of cylinders will be fired (1 & 4 or 2 & 3). It then tells the ICM which cylinder to fire through the ignition control circuits.
