Alero L4-144 2.4L DOHC VIN T SFI (2000)
Ignition Control Module: Description and Operation
Ignition Control (IC)
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.
^
The 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 the crankshaft position, the engine speed and the injector pulse
width. The engine will not start or run if this circuit is open or grounded.
^
The reference low - This wire is grounded through the ICM and ensures 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).
^
The 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, the module will determine which pair of cylinders will be fired (1 & 4 or 2 & 3). The module then tells the ICM which
cylinder to fire through the ignition control circuits.
