Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP
The ignition control module (ICM) has independent power and ground circuits. The circuits between the ICM and the powertrain control module (PCM) consists of the following circuits:
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 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:
The engine speed is more than 600 RPM.
The engine will start and may run with the ICM controlling the spark timing.
If the condition is intermittent, refer to Intermittent Conditions .
Schematic Reference: Engine Controls Schematics
Did you perform the Diagnostic System Check-Engine Controls?
Go to Step 2
Go to Diagnostic System Check - Engine Controls
Does the DTC fail this ignition?
Go to Step 3
Go to Intermittent Conditions
Does the test lamp illuminate?
Go to Step 6
Go to Step 4
Check low reference circuit for open.
Did you find and correct the condition?
Go to Step 5
Check for poor terminal connections at ICM. Refer to Testing for Intermittent and Poor Connections in Wiring Systems.
Go to Step 7
Does the voltage measure within the specified range?
Go to Step 8
Go to Step 12
Go to Step 9
Test for poor terminal connections at the PCM. Refer to Testing for Intermittent and Poor Connections in Wiring Systems.
Go to Step 11
Test for poor terminal connections at the Ignition Control (IC) Module. Refer to Testing for Intermittent and Poor Connections in Wiring Systems.
Go to Step 10
Replace the ICM. Refer to Ignition Control Module Replacement .
Did you complete the replacement?
Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement .
Does the DTC run and pass?
Go to Step 13
With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?
Go to Diagnostic Trouble Code (DTC) List