Circuit Description
The crankshaft position (CKP) sensor sends pulses to the powertrain control module (PCM) as the reluctor wheel teeth rotate past the CKP sensor. The PCM uses the CKP pulses to synchronize the ignition and fuel injector operation, and to time the interval between each CKP pulse. The PCM determines when an excessive change in crankshaft speed occurs by comparing each new time interval with the previous interval. A misfire causes an unexpected change in the crankshaft speed. A certain amount of acceleration or deceleration is expected between each firing stroke, but if the crankshaft speed changes more than an expected amount, the PCM interprets this as a misfire. The interval between CKP sensor pulses is extremely small. At high engine speeds, slight variations in the following components make misfire detection difficult:
| • | The crankshaft |
| • | The reluctor wheel |
| • | The CKP sensor |
The PCM learns variations during the crankshaft position system variation learn procedure. The PCM compensates for these variations when performing misfire calculations. Only a scan tool can command the PCM to perform the crankshaft position system variation learn procedure again.
Perform the learning procedure after the following actions:
| • | A PCM replacement |
| • | Any operation or repair involving the crankshaft, the CKP sensor, or the CKP sensor to reluctor wheel gap relationship |
| • | An engine replacement |
| • | The ignition switch is in the ON position until the battery is drained |
Important: A PCM power disconnect with the ignition ON may erase the stored pulse value and set diagnostic trouble code (DTC) P1336.
Disconnecting the PCM will not erase the learned crankshaft position system variation as long as the ignition switch is in the OFF position.
Important: Reprogramming the PCM does not require running the crankshaft position system variation learn procedure unless the PCM is new.
DTC P1336 sets if the crankshaft position system variation is not within an acceptable range, or can not be learned.
Conditions for Running the DTC
DTCs P0335, P0336, P0341, or P1345 are not set.
Conditions for Setting the DTC
The PCM has not learned the Crankshaft Position System Variation.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/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
Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
If the crankshaft position system variation learn procedure cannot be learned, check for the following conditions:
| • | A chipped or damaged reluctor wheel |
| • | Incorrect alignment of the CKP sensor to the reluctor wheel |
| • | Excessive crankshaft run-out |
| • | Interference in the signal circuit to the CKP sensor |
| Important: If the PCM receives an incorrect crankshaft to camshaft pulse ratio, the PCM will not allow the scan tool to enable the learn procedure. |
| • | Incorrect ratio of crankshaft to camshaft pulses |
The misfire diagnostic is not operable when the engine speed is above 1,000 RPM and DTC P1336 is set.
When the learn procedure is in progress and the engine speed is at 4,000 RPM, a decrease in engine speed will occur. During the engine coast down, the PCM monitors the CKP sensor signal and stores the pattern. This pattern is used to determine if the crankshaft speed variations are due to misfire.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The PCM enables the learn process after the engine coolant temperature of 65°C (150°F) is reached. Engine deceleration occurs when the learn procedure is in progress. The PCM monitors and records the CKP sensor signal during engine coast-down conditions.
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Test in Progress on the scan tool indicates the PCM is performing the learn procedure. The learn procedure will not be allowed if the PCM receives the following information:
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If a repair is necessary due to a condition which prevented the learn procedure from enabling, the crankshaft position system variation learn procedure must be performed.
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The ignition must be in the OFF position for at least 10 seconds after the learn procedure is complete and the engine RPM has returned to idle. The PCM saves the signal data after these conditions are met.
| • | An incorrect crankshaft to camshaft pulse ratio |
| • | An incorrect transmission range signal input |
| • | Corrupted class 2 communication |
| • | No change in the brake switch input |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
|
Important: If there are any other DTCs set, diagnose before proceeding with this table. Perform the crankshaft position system variation learn procedure as follows.
Important: While the learn procedure is in progress, release the throttle immediately when the engine starts to decelerate. The engine control is returned to the operator and the engine will respond to throttle position after the learn procedure is complete. Does the scan tool indicate Learn Status as Learned This Ignition? | 65°C (150°F) 4,000 RPM | Go to Step 5 | Go to Step 3 | |
Attempt the crankshaft position system variation learn procedure as many times as the specified value. Does the scan tool indicate Learn Status as Learned This Ignition? | 3 | Go to Step 5 | Go to Step 4 | |
Inspect the crankshaft position (CKP) sensor and the crankshaft reluctor wheel for damage. Refer to Diagnostic Aids. Did you find the condition? | -- | Go to Step 6 | Go to Diagnostic Aids | |
Turn OFF the ignition for 15 seconds. Is the action complete? | -- | Go to Step 7 | -- | |
6 | Replace the CKP sensor or the reluctor wheel. Refer to Crankshaft and Bearing Removal in Engine Mechanical 4.3L. Is the action complete? | -- | Go to Step 7 | -- |
7 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | Go to Step 8 | Go to Step 2 |
8 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
