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 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. The PCM will switch from Angle Based mode to Time Based Mode A using CKP sensor A signal input. If the PCM detects no CKP sensor B signal, DTC P0385 sets.

This diagnostic procedure supports the following DTC:

DTC P0385 Crankshaft Position (CKP) Sensor B Circuit

The PCM detects an incorrect number of CKP sensor pulses in a given number of CMP sensor pulses for more than 2 seconds or the PCM detects a CKP match has not occurred within the last 2 seconds.

The following conditions may cause this DTC to set:

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:

An improperly installed crankshaft could cause excess crankshaft end play.

If the condition is intermittent, refer to Intermittent Conditions .

Ignition system DTCs set with the ignition in the Start position if the starter relay or the starter is inoperative. When the PCM enables starter operation, the PCM also initiates the diagnostic test routines for DTCs P0335, P0340, and P0385. If a condition exists which prevents the engine from cranking, the PCM will not receive signal input from the CKP and CMP sensors, and the DTCs will set.

If DTC P0615 is set, diagnose DTC P0615 first. If DTC P0335, P0340, and/or P0385 are set and no condition is found, inspect for the following conditions:

Procedures for Selecting Crank Position Sensing Decode Mode

When diagnosing the CKP 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:

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) 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 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.

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

2. This step determines if the 12-volt reference circuit to the CKP A, CKP B, and the CMP is shorted to a ground. If all 3 DTCs are set, this indicates the circuit is shorted to a ground or a sensor is internally shorted. All 3 DTCs set because the 12-volt reference circuit are internally connected within the PCM. The engine will not start with this condition.

3. DTC P0336 indicates an intermittent loss of CKP sensor A signal while in Time A mode. DTC P0336 only sets after the PCM detects a loss of CKP sensor B signal and has switched to Time A mode.

   During normal operation, the PCM uses the Angle Mode to determine 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 CKP sensor A signal, the PCM switches to a Time B mode using CKP sensor B input to determine engine position. If the PCM detects a loss of CKP sensor B, the PCM switches to a Time A mode using CKP sensor A input to determine engine position.

4. During engine operation, if moving the harnesses and connectors related to CKP sensor B results in a switch to Time A mode, an intermittent condition in the harnesses or connectors is present. This may cause an engine stall condition. If the harnesses and connectors are OK, CKP sensor B may be the cause of the intermittent condition.

7. In order to test the CKP sensor B signal circuit, the PCM must be commanded to Time B mode using the scan tool. This allows the PCM to monitor input signals from CKP sensor B. Refer to Diagnostic Aids for the procedures to selecting the Crank Decode Mode.