The powertrain control module (PCM) uses the 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 in order 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 the CKP A or the 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 the signal pulses from both CKP sensors. The PCM uses the signal pulses in order to determine an initial crankshaft position, and to generate the MEDRES (24X reference) and the LORES (4X reference) signals. When 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 if the MEDRES to CMP signal correlation is correct, the PCM determines that the CKP sensor A is at fault. However, if the MEDRES to CMP correlation is incorrect, the PCM determines that the CKP sensor B is at fault. If the PCM determines that the CKP sensor A is at fault, DTC P0335 will set. The PCM will switch from angle-based mode to time-based Mode B using the CKP sensor B signal input. If, after switching to time-based Mode B, the PCM detects an intermittent loss of CKP sensor B signal, diagnostic trouble code (DTC) P0386 will set.

The PCM detects an intermittent loss of the CKP sensor B signal.

If the condition is intermittent, refer to Intermittent Conditions .

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 in order perform the following steps:

1. Turn the ignition to the RUN/ON position.
2. Select Engine Output Controls.
3. Select Crank Position Sensing Decode Mode.
4. Select the desired mode (Angle, Time A, or Time B), and press 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 cannot be commanded with the engine running, or after commanding a desired decode mode. In order to command a different decode mode, you must cycle the ignition OFF and ON.

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

2. During normal operation, the PCM uses the Angle Mode in order to determine the engine position. In order to operate in this mode, the PCM must receive valid input from both CKP sensors. If the PCM detects a loss of the CKP sensor A signal, the PCM switches to a Time B Mode using the CKP sensor B input in order to determine the engine position. If the PCM detects a loss of the CKP sensor B, the PCM switches to a Time A Mode using the CKP sensor A input in order to determine the engine position. If the PCM detects a loss of the CKP sensor A signal, DTC P0335 will set. DTC P0386 will only set if a problem occurs with the CKP sensor B occurs in Time B Mode. DTC P0335 must be diagnosed first.

6. In order to properly verify any repair to the CKP sensor A harnesses and/or connectors, the system must be commanded to operate in Time B mode. This procedure forces the PCM to use CKP sensor B i order to determine engine position. If the system is functioning normally, DTC P0386 should not reset.