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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2000 🢒 Seville 🢒 DTC 🢒 DTC P1372 Crankshaft Position (CKP) Sensor A-B Correlation

Circuit Description

The 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 PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test runs and fails.
    • The PCM stores the conditions present when the DTC set as Freeze Frame/Failure Records data.

Conditions for Clearing the MIL/DTC
    • The PCM will turn the MIL OFF after the third consecutive trip in which the diagnostic runs and passes.
    • The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
    • The DTC can be cleared by using the scan tool Clear DTC Information function.

Diagnostic Aids

If the condition is intermittent, refer to Intermittent Conditions 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). To enable a specific crank decode, using the scan tool, 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.

  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

Values

Yes

No

1

Did you perform the Powertrain On Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

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 scan tool indicate that DTC P1372 failed last test?

--

Go to Step 4

Go to Step 3

3
  1. Review and record the scan tool Fail Records Information.
  2. Operate the vehicle within the Fail Records conditions.
  3. With the scan tool, monitor the Specific DTC Information for DTC P1372.

Does the scan tool indicate DTC P1372 failed last test?

--

Go to Step 4

Go to Diagnostic Aids

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 Crankshaft Position (CKP) Sensor B Performance

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.
  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 Crankshaft Position (CKP) Sensor A Performance

Go to Diagnostic Aids