How to Relearn a Procedure on a GMC After Changing the Crankshaft Sensorby Kyle Sanstrom
The crankshaft sensor on GMC vehicles is synced to the powertrain control module, or PCM. When the crank sensor is replaced, it must be resynced to the PCM. Without resyncing, the PCM cannot properly determine the position of the crankshaft. The proper procedure for resyncing or relearning the crankshaft position is called the "CKP Variation Learn." The CKP Variation Learn procedure resets the positional information in the PCM's memory and replaces it with updated information from the new crankshaft sensor.
Shift the GMC vehicle's transmission into park, or first gear for a manual transmission. Apply the parking brake and leave the engine running.
Plug an automotive scan tool's data connector into the vehicle's diagnostic data port. This port is situated underneath the dashboard on the driver's side of the vehicle, to the right of the steering column.
Power on the scan tool and select "PCM" from the main welcome menu. Select "Special Functions" from the secondary screen, then choose "CKP Variation Learn" from the "Special Functions" menu.
Allow the scan tool to perform the CKP Variation learn procedure. This can take up to 10 minutes. Do not turn off the engine or disconnect the scan tool during this procedure.
Remove the scan tool. Turn the engine off, then back on again. Verify that the engine runs smoothly.