Circuit Description
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 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 |
Conditions for Running the DTC
The engine speed is greater than 600 RPM.
Conditions for Setting the DTC
| • | The PCM detects an open in the IC control circuit. |
| • | The condition is present for 300 3X reference periods, 100 crankshaft revolutions. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
The engine will start and may run with ICM controlling spark timing.
If the condition is intermittent, refer to Intermittent Conditions .
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 |
Does the DTC fail this ignition? | -- | Go to Step 3 | Go to Intermittent Conditions |
3 |
Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 4 |
4 | Inspect low reference circuit for an open. Did you find and correct the condition? | -- | Go to Step 6 | Go to Step 5 |
5 | Inspect for poor terminal connections at the ICM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 6 | Go to Step 7 |
6 |
Does the voltage measure within the specified range? | 20-40 mV | Go to Step 8 | Go to Step 7 |
7 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 |
8 | Test for poor terminal connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 |
9 | Test for poor terminal connections at the ICM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 |
10 | Replace the ICM. Refer to Ignition Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
12 |
Does the DTC run and pass? | -- | Go to Step 13 | Go to Step 2 |
13 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
