GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2001 🢒 Eldorado 🢒 Engine 🢒 Engine Controls - 4.6L 🢒 DTC P1372

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 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 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 to Intermittent Conditions .

Procedures for Selecting Crank Position Sensing Decode Mode

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

When diagnosing the crankshaft position sensors, may be necessary to enable a specific decode mode, Angle, Time A, or Time B. In order to enable a specific crank decode, using the scan tool, perform the following steps:

  1. Turn ON the ignition.
  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.

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 to determine 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 to determine engine position. An intermittent problem with CKP sensor A and/or related harnesses/connectors will set DTC P0336.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2
  1. Start the engine.
  2. Allow the engine to reach normal operating temperature.
  3. With the scan tool, monitor the specific DTC information for DTC P1372.

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 as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Does the scan tool indicate that the DTC passed?

Go to Intermittent Conditions

Go to Step 4

4

  1. Leave the scan tool installed.
  2. Turn ON the ignition, with the engine OFF.
  3. Command Time Mode B using the scan tool. Refer to Procedures for Selecting Crank Position Sensing Decode Mode in Diagnostic Aids.
  4. Start engine.
  5. Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  6. Wiggle the harnesses and connectors related to CKP sensor B.
  7. With the scan tool, monitor the Specific DTC Information for DTC P0386.

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

Go to DTC P0386

Go to Step 5

5

  1. Leave the scan tool installed.
  2. Turn ON the ignition, with the engine OFF.
  3. Command Time Mode A using the scan tool. Refer to Procedures for Selecting Crank Position Sensing Decode Mode in Diagnostic Aids.
  4. Start engine.
  5. Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  6. Wiggle the harnesses and connectors related to CKP sensor A.
  7. With the scan tool, monitor the Specific DTC Information for DTC P0336.

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

Go to DTC P0336

Go to Step 6

6
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30  seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 7

Go to Intermittent Conditions

7

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

System OK