Rick's Free Auto Repair Advice

Crankshaft Sensor Relearn

Crankshaft Sensor Relearn — why it’s required

Why you must perform a crankshaft sensor relearn after replacing the crankshaft sensor

A crank relearn is a process that the PCM goes through to

crankshaft position sensor

Crankshaft position sensor

recalibrate its knowledge of the relationship between the crankshaft and camshaft. That’s necessary because the crankshaft and camshaft are connected by a timing chain or timing belt. Over time, the timing chain/belt can stretch and that stretch changes the relationship and timing between the crankshaft and camshaft.

If the change/stretch is great enough, the PCM will notice discrepancies between the commanded valve timing adjustments and the actual valve timing. That difference can cause misfires like P0300 or specific cylinder misfires.

Performing a crank relearn doesn’t fix the timing chain/belt stretch, but it does allow the PCM to learn about the stretch that’s occurred since the car was manufactured and adjust its valve timing commands.

Crankshaft sensor relearn is called different terms by different car makers

Carmakers refer to this relearn procedure using different terminology, but it’s all pretty much the same thing.

Reset Adaptive Enumerators
Misfire profile relearn
Fire profile relearn
Toothed wheel correction factor

When to perform a crankshaft sensor relearn procedure

You must perform a crank relearn any time you replace the following components:

Timing Chain or gears
Balancer shaft or gear
Timing chain tensioner
PCM, ECM or module replacement

When you see a P0300- carmakers are now recommending a crankshaft position sensor relearn before diagnosing a P0300 condition. They want you to eliminate the possibility of a timing chain stretch as the cause of the random misfire BEFORE you start digging into other possibilities.

You’ll need a bi-directional scan tool to perform a crank relearn

How to perform a crankshaft sensor relearn

The exact procedure varies by car maker. On some vehicles, you enter the procedure on your scan tool and it wipes out the adaptive memory and starts to perform the relearn by itself. On other vehicles, you wipe out adaptive memory and then perform a specific drive cycle so the PCM can relearn. Refer to a shop manual for the exact procedure for your year, make, model and engine.

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