P0385

CIRCUIT DESCRIPTION
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 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 the signal pulses from both CKP sensors. The PCM uses the signal pulses in order to determine an initial crankshaft position, and in order 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 CKP sensor A is at fault. If the MEDRES to CMP correlation is incorrect, the PCM determines that CKP sensor B is at fault. If the PCM determines that CKP sensor B is at fault, diagnostic trouble code (DTC) P0385 will set. The PCM will switch from angle-based mode to time-based Mode A using the CKP sensor A signal input.

CONDITIONS FOR RUNNING THE DTC
The engine is cranking or running.

CONDITIONS FOR SETTING THE DTC
The PCM detects a loss of the CKP sensor B signal.

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 . Intermittent Conditions

If the starter relay is inoperative or if the starter is inoperative, the ignition system DTCs set with the ignition in the START position. 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 the signal input from the CKP sensor and the 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 trouble is found, check for the following conditions:
- A no-crank condition or an intermittent no-crank condition
- An attempt to crank the engine with the shift lever not in P/N

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 ) 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.

TEST DESCRIPTION

Steps 1-4:

Steps 5-8:

Steps 9-12:

Steps 13-18:

Steps 19-22:

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, the CKP B, and the CMP is shorted to a ground. If all 34 DTCs are set, the circuit is shorted to a ground, or a sensor is internally shorted. All 3 DTCs set because the 12-volt reference circuits are internally connected within the PCM. The engine will not start with this condition.
3. DTC P0336 indicates an intermittent loss of the CKP sensor A signal while in Time A mode. DTC P0336 only sets after the PCM detects a loss of the CKP sensor B signal and has switched to Time A mode.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 signal, the PCM switches to a Time A mode using the CKP sensor A input in order to determine the engine position.
4. During engine operation, if moving the harnesses and connectors that are related to CKP sensor B results in a switch to Time A mode may also causes an engine stall condition, an intermittent condition in the harnesses or in the connectors is present. If the harnesses and the 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 the input signals from CKP sensor B. Refer to Diagnostic Aids for the procedures for selecting the Crank Decode Mode.
11. This step determines if the CMP sensor is shorted internally. If the 12-volt reference parameter changes from Fault to OK, the condition is with the sensor.
12. This step determines if the CKP A sensor is shorted internally. If the 12-volt reference parameter changes from Fault to OK, the condition is with the sensor.
13. This step determines if the CKP B sensor is shorted internally. If the 12-volt reference parameter changes from Fault to OK, the condition is with the sensor.