The crankshaft position (CKP) sensor is mounted in the front of the engine behind the harmonic balancer. The CKP sensor works in conjunction with a 3X (4X on V8 applications) reluctor wheel mounted on the front of the crankshaft. The CKP sensor has a B+ power supply, a ground, and a signal circuit.

As the crankshaft rotates, the reluctor wheel teeth interrupt a magnetic field produced by a magnet located in the sensor. The sensors internal circuitry detects this field and produces a frequency which the control module monitors on the signal circuit. The control module uses this signal in order to accurately measure crankshaft velocity, which is important to ignition control spark timing, fuel injector timing, and for misfire detection.

The control module can detect small variations in the CKP sensor and reluctor wheel. These part tolerances must be learned by the control module before an accurate CKP signal can be determined. At high engine speeds, slight variations in the following components make misfire detection difficult:

The control module learns variations during the Crankshaft Position System Variation Learning Procedure, and compensates for these variations when performing misfire calculations. Only a scan tool can command the control module to perform the Crankshaft Position System Variation Learning Procedure.

Perform the learning procedure after the following actions:

Important: A control module power disconnect with the ignition ON may erase the stored pulse value and set the DTC P1336.

Disconnecting the control module will not erase the learned crankshaft position system variation as long as the ignition switch is in the OFF position.

Important: Reprogramming the control module does not require running the Crankshaft Position System Variation Learn Procedure unless the module is new or from another vehicle.

If the crankshaft position system variation is not within an acceptable range, or can not be learned, DTC P1336 sets.

The VCM has not learned the crankshaft position system variation.

The VCM will illuminate the Malfunction Indicator Lamp (MIL) on the first drive trip that the diagnostic runs and fails.

If the Crankshaft Position System Variation Learn Procedure cannot be learned, check for the following conditions:

Engine diagnostic misfire is not operable when the engine 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 coastdown, the VCM monitors the CKP sensor signal and stores the pattern. This pattern is used to determine if the crankshaft speed variations are due to misfire.

The number(s) below refer to the step number(s) on the diagnostic table.

2. The VCM enables the learn process after 65°C (150°F) is reached. Engine deceleration occurs when the learn procedure is in progress. The VCM monitors and records the CKP sensor signal during engine coastdown conditions.

3. TEST IN PROGRESS on the scan tool indicates the VCM is performing the learn procedure. If the VCM receives an incorrect crankshaft to camshaft pulse ratio, an incorrect transmission range signal input, corrupted communication, or no change in the brake switch input, the learn procedure will not be allowed.

4. If a repair is necessary due to a condition which prevented the learn procedure from enabling, the Crankshaft Position System Variation Learning Procedure must be performed.

5. The ignition must be in the OFF position for at least 15 seconds after the learn procedure is complete and the engine RPM has returned to idle. The VCM saves the signal data after these conditions are met.