Circuit Description
The powertrain control module (PCM) uses dual crankshaft position (CKP A and CKP B) sensors to determine crankshaft position. The PCM supplies an ignition voltage and a ground for each sensor. During engine rotation, a slotted ring, machined into the crankshaft, causes the sensors to return a series of ON and OFF pulses to the PCM. The PCM uses these pulses to decode the position of the engine crankshaft.
The PCM uses two basic methods of decoding the engine position: Angle Based and Time Based (using either CKP A or CKP B sensor input). During normal operation, the PCM uses the angle based method. In order to operate in this mode, the PCM must receive signal pulses from both CKP sensors. The PCM uses the signal pulses to determine an initial crankshaft position, and to generate MEDRES (24X reference) and LORES (4X reference) signals. Once the initial crank position is determined, the PCM continuously monitors both sensors for valid signal inputs. As long as both signal inputs remain, the PCM will continue to use the angle based mode.
When either CKP signal is lost, the PCM will compare the MEDRES signal to the camshaft position (CMP) sensor signal. If the PCM detects a valid CMP signal, and the MEDRES to CMP signal correlation is correct, the PCM determines that CKP sensor A is at fault. However, if the MEDRES to CMP correlation is incorrect, the PCM determines that CKP sensor B is at fault. If, while in the angle based mode, the PCM detects an intermittent loss of either CKP signal, DTC P1372 will set.
Conditions for Running the DTC
| • | The engine is cranking or running. |
| • | The PCM is operating in the Angle Based mode of decoding the engine position. |
Conditions for Setting the DTC
The PCM detects an intermittent loss of signal input from either sensor.
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
If the condition is intermittent, refer Intermittent Conditions to in Symptoms.
Procedures for Selecting Crank Position Sensing Decode Mode
When diagnosing the crankshaft position sensors, it may be necessary to enable a specific decode mode (Angle, Time A, or Time B). In order to enable a specific crank decode, use the scan tool, and perform the following steps:
| • | Turn ON the ignition. |
| • | Select Engine Output Controls. |
| • | Select Crank Position Sensing Decode Mode. |
| • | Select the desired mode (Angle, Time A, or Time B) by pressing SELECT STATE. |
| • | Command the decode mode by pressing COMMAND STATE. |
The commanded state remains valid for the current ignition cycle. A specific decode mode can not be commanded with the engine running, or after commanding a desired decode mode. To command a different decode mode, you must cycle the ignition OFF and ON.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
In time based B mode, the PCM uses CKP sensor B to determine engine position. An intermittent problem with CKP sensor B and/or related harnesses or connectors will set DTC P0385.
-
In time based A mode, the PCM uses CKP sensor A in order to determine the engine position. An intermittent problem with CKP sensor A and/or the related harnesses or connectors will set DTC P0335.
Step | Action | 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 4 | Go to Step 3 |
3 |
Does the DTC fail this ignition? | Go to Step 4 | Go to Diagnostic Aids |
Does the CKP sensor status change to Time A? | Go to DTC P0385 | Go to Step 5 | |
Does the CKP sensor status change to Time B? | Go to DTC P0335 | Go to Step 6 | |
6 |
Does the DTC run and pass? | Go to Step 7 | Go to Step 2 |
7 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | System OK | |
