Circuit Description
The powertrain control module (PCM) uses dual crankshaft position (CKP A and CKP B) sensors in order 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 the PCM determines that CKP sensor B is at fault, DTC P0385 will set. The PCM will switch from angle based mode to Time Based Mode A using CKP sensor A signal input.
Conditions for Running the DTC
| • | The engine is cranking or running. |
| • | DTC P0340 or P0341 are not set. |
Conditions for Setting the DTC
The PCM detects an intermittent loss of 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 .
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 trouble is found, check for the following conditions:
| • | Is there a no-crank condition or an intermittent no-crank condition? |
| • | Was an attempt made to crank the engine with the shift lever not in P/N? |
Procedures for Selecting Crank Position Sensing Decode Mode
Diagnosing the crankshaft position sensors may require enabling 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 the ignition to the RUN/ON position. |
| • | Select Engine Output Controls. |
| • | Select Crank Position Sensing Decode Mode. |
| • | Select the desired mode (Angle, Time A, or Time B) and press 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.
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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.
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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 in order 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 in order 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.
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During engine operation, if moving the harnesses and connectors related to CKP sensor B results in a switch to Time A mode, may also cause an engine stall condition, an intermittent condition in the harnesses or connectors is present. If the harnesses and connectors are OK, CKP sensor B may be the cause of the intermittent condition.
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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.
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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.
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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.
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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.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics | |||
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |
Are all three DTCs P0335, P0340, and P0385 also set? | Go to Step 11 | Go to Step 3 | |
Does the scan tool indicate the CKP sensor status as ANGLE? | Go to Step 4 | Go to Step 5 | |
Did you find and correct the condition? | Go to Step 21 | Go to Diagnostic Aids | |
5 |
Does the test lamp illuminate? | Go to Step 6 | Go to Step 8 |
6 | Connect the test lamp between the 12-volt reference circuit of the CKP B sensor and the low reference circuit of the CKP B sensor. Does the test lamp illuminate? | Go to Step 7 | Go to Step 9 |
Does the scan tool indicate an RPM while touching the test lamp to the signal circuit? | Go to Step 15 | Go to Step 10 | |
8 |
Did you find and correct the condition? | Go to Step 21 | Go to Step 16 |
9 |
Did you find and correct the condition? | Go to Step 21 | Go to Step 16 |
10 |
Did you find and correct the condition? | Go to Step 21 | Go to Step 16 |
Does the scan tool display OK? | Go to Step 17 | Go to Step 12 | |
Does the scan tool display OK? | Go to Step 18 | Go to Step 13 | |
Does the scan tool display OK? | Go to Step 19 | Go to Step 14 | |
14 |
Did you find and correct the condition? | Go to Step 21 | Go to Step 20 |
15 | Inspect for poor connections at the harness connector of the CKP B sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 21 | Go to Step 19 |
16 | Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 21 | Go to Step 20 |
17 | Replace the CMP sensor. Refer to Camshaft Position Sensor Replacement . Did you complete the replacement? | Go to Step 21 | -- |
18 | Replace the CKP sensor A. Refer to Crankshaft Position Sensor Replacement . Did you complete the replacement? | Go to Step 21 | -- |
19 | Replace the CKP sensor B. Refer to Crankshaft Position Sensor Replacement . Did you complete the replacement? | Go to Step 21 | -- |
20 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | Go to Step 21 | -- |
21 |
Does the DTC run and pass? | Go to Step 22 | Go to Step 2 |
22 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | System OK | |
