CKP Variation Learn:
Eliminate False Misfire DTC's

DTC P1336 indicates that CKP System Variation is not learned. This learn procedure is needed to compensate for minor variations in manufacturing tolerances that might alter the relationship of the crankshaft position sensor to the reluctor wheel, possibly resulting in a false misfire DTC and MIL illumination.

CKP positions must be relearned when any of these parts are removed or replaced:

• CKP sensor
• Front cover or bracket holding the crankshaft position sensor
• Target wheel (reluctor)
• Crankshaft
• Engine block
• Engine assembly
• PCM

The crankshaft position system variation learning feature is used to calculate reference period errors caused by slight tolerance variations in the crankshaft, the crankshaft balancer interrupter rings, and the crankshaft position sensor Hall Effect switches. The calculated error allows the PCM to accurately compensate for reference period variations. The crankshaft position system variation learning feature enhances the ability of the PCM to detect misfire events over a wider range of engine speed and load.

The crankshaft position system variation values are stored in the PCM non-volatile memory after the crankshaft position system variation learn procedure has been performed. DTC P1336 set indicates that the crankshaft position system variation values have not been stored in the PCM and the crankshaft position system variation learn procedure must be performed. The learn procedure is required after the following service procedures have been performed, regardless of whether or not DTC P1336 is set:

• PCM replacement
• Engine replacement
• Crankshaft replacement
• Crankshaft balancer replacement
• Crankshaft position sensor replacement
• Any engine repair(s) which disturbs the crankshaft/harmonic balancer to crankshaft position sensor relationship

Conditions for Running the DTC

• No CMP or CKP sensor DTC(s) set.
• Coolant temp greater than 70º C.

Conditions for Setting the DTC

• Crankshaft position system variation values are not stored in the PCM memory.

Action Taken When the DTC Sets

• The PCM will illuminate the MIL during the first trip in which the diagnostic test has been run and failed.
• The PCM will store conditions which are present when the DTC sets as Freeze Frame and Fail Records data.

Conditions for Clearing the MIL/DTC

• The PCM will turn the MIL “OFF” during the third consecutive trip in which the diagnostic has been run and passed.
• The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
• The DTC can be cleared by using the Scan Tool Clear Info function or by disconnecting the PCM battery feed on some models.

If a PCM is swapped from one vehicle into another, the CKP position variation must be relearned also (unless the PCM will be returned to the original vehicle). If a PCM is swapped without a CKP learn, the P1336 will not set and it is possible that a misfire DTC in the P0300 group might later set falsely. This is due to an incorrect CKP position value being stored in the PCM and being used in misfire calculation.

CKP variation is only relearned with a scan tool. It does not relearn “by itself.”

1. Make sure no DTCs are set. If DTCs
   are set, service them before performing the procedure.
2. The service brake must be firmly applied and the transmission in Park for an automatic or Neutral for a manual.
   
3. A/C must be “OFF” and the hood closed.
   
4. At this point, use the scan tool and select CASE Learn:
   
5. Open the accelerator to the CASE fuel cutoff speed and release it as soon as the PCM cuts off the fuel and the engine begins to decelerate.
   
6. The scan tool will identify when the procedure is complete.