GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 DeVille 🢒 Accessories 🢒 Navigation Systems 🢒 DTC P1372

Circuit Description

The powertrain control module (PCM) uses dual crankshaft position (CKP)  A and CKP B sensors in order to determine the 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 2 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 medium resolution (24X reference) and low resolution (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 medium resolution signal to the camshaft position (CMP) sensor signal. If the PCM detects a valid CMP signal, and the medium resolution to CMP signal correlation is correct, the PCM determines that CKP sensor A is at fault. However, if the medium resolution 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.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1372 Crankshaft Position (CKP) Sensor A-B Correlation

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.
    • DTC P1372 runs continuously once the above conditions are met.

Conditions for Setting the DTC

The PCM detects 5 CKP resyncs occurred within 10 seconds.

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 following conditions may cause this DTC to set:

    • The crankshaft reluctor wheel is damaged or improperly installed.
    • The sensor is coming in contact with the reluctor wheel.
    • If the crankshaft rotates backwards, this DTC sets. This condition is only with vehicles equipped with a manual transmission. This condition can occur when a vehicle is on an incline and the clutch is released and an engine stall occurs.

Excess crankshaft end play will cause the CKP sensor reluctor wheel to move out of alignment with the CKP sensor. This could result in any of the following conditions:

    • A no start
    • A start and stall
    • Erratic performance

An improperly installed crankshaft could cause excess crankshaft end play.

Procedures for Selecting Crank Position Sensing Decode Mode

If both intermittent codes DTC P0336 and DTC P0386 set in addition to DTC P1372, check the time mode in order to determine which sensor is good.

When diagnosing the CKP sensors, enabling a specific decode mode (Angle, Time A, or Time B) may be necessary . In order to enable a specific crank decode, use the scan tool in order to perform the following steps:

  1. Turn ON the ignition, with the engine OFF.
  2. Select Engine Output Controls.
  3. Select Crank Position Sensing Decode Mode.
  4. Select the desired mode (Angle, Time A, or Time B) by pressing SELECT STATE.
  5. 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.

If the condition is intermittent, refer to Intermittent Conditions .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. In time based B mode, the PCM uses CKP sensor B in order to determine the engine position. An intermittent problem with CKP sensor B and/or related harnesses/connectors will set DTC P0386.

    2.

  2. 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 related harnesses and connectors will set DTC P0336.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Start the engine.
  2. Allow the engine to reach normal operating temperature.
  3. Observe the DTC information parameter with the scan tool.

Does the DTC fail this ignition?

Go to Step 4

Go to Step 3

3
  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 4

Go to Diagnostic Aids

4

  1. Turn ON the ignition, with the engine OFF.
  2. Command Time Mode B using the scan tool. Refer to Procedures for Selecting Crank Position Sensing Decode Mode in Diagnostic Aids.
  3. Start engine.
  4. Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  5. Wiggle the harnesses and connectors related to crankshaft position (CKP) sensor B.
  6. Observe the DTC Information parameter with the scan tool.

Does the scan tool indicate that DTC P0386 failed last test?

Go to DTC P0386

Go to Step 5

5

  1. Turn ON the ignition, with the engine OFF.
  2. Command Time Mode A using the scan tool. Refer to Procedures for Selecting Crank Position Sensing Decode Mode in Diagnostic Aids.
  3. Start engine.
  4. Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  5. Wiggle the harnesses and connectors related to CKP sensor A.
  6. Observe the DTC Information parameter with the scan tool.

Does the scan tool indicate that DTC P0336 failed last test?

Go to DTC P0336

Go to Step 6

6
  1. Lower the vehicle.
  2. Clear the DTCs with a scan tool.
  3. Turn OFF the ignition for 30 seconds.
  4. Start the engine.
  5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 7

Go to Diagnostic Aids

7

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK