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What Happens if You Don’t Relearn a Crankshaft Position Sensor? (Explained)

Updated: Jan 9

The crankshaft position sensor informs the engine control unit (ECU) of where the crankshaft is, this ensures the engine is in sync (ignition timing, fuel injection, etc.). If this sensor fails, it leads to a slew of issues. It is advised that the crankshaft position sensor be relearned if it's replaced.

If the crankshaft position sensor is not relearned, the ECU may not know the position of the crankshaft. This can cause issues like that of a faulty sensor, such as a poorly running engine, stalling, failing to start, increased vibrations, and may result in engine damage.

The process of relearning the crankshaft sensor is relatively simple and takes less than 30 minutes. To relearn the sensor, you'll need a professional OBD tool that can interface with the ECU. The procedure is simple, requiring just that you follow the directions on the screen.


Table of Contents:

OBD scanner being used in a vehicle

When You Should Relearn a Crankshaft Position Sensor

This sensor functioning correctly is essential for the engine to work properly. You may need to relearn a crankshaft sensor for the following reasons.

  • The crankshaft position sensor has been replaced

  • The ECU has been replaced

  • The battery has been replaced

Once a new crankshaft sensor has been installed it must be relearned so the ECU knows the crankshafts precise location. This may also need to be done if the ECU or battery has been replaced with a new one.

Failure to Relearn Crankshaft Sensor

Failing to relearn the crankshaft position sensor can result in various issues, such as the following.

  • Illumination of the check engine light (CEL)

  • Reduced engine performance

  • Worsened fuel efficiency

  • Difficulty starting the engine

  • Rough idle and increased vibrations

  • Shuddering, shaking and jerking

  • Stalling

  • Misfiring

You'll notice the check engine light come on, the engine will run poorly with reduced power, increased vibrations, it may stall or fail to start. If you leave the engine running in this condition it can cause engine knocking and may even result in engine damage.

The symptoms associated with not relearning a new sensor are basically the same as those you'll find when a vehicle has a faulty crankshaft position sensor.

How to Relearn a Crankshaft Position Sensor

The steps to relearn a crankshaft position sensor will vary depending on the vehicle and the OBD scanner you use, the following steps are a generalised guide. It is usually quite simple to do requiring only an advanced OBD scanner.

  1. Connect the OBD tool to the vehicle's diagnostic port. The diagnostic port is usually found somewhere under the dashboard on the drivers side, less commonly it's found around the centre console or under the dashboard on the passenger side.

  2. Turn on the ignition but do not start the engine.

  3. On the OBD tool, choose the "Relearn Crankshaft Position Sensor" function. If you do not have this function on your OBD scanner you will need a more advanced one (like this one).

  4. Follow the instructions shown on the scanner.

  5. Turn on the engine and let it idle for a few minutes.

  6. Disconnect the OBD scanner and turn off the engine.

> See step-by-step how to relearn a crankshaft position sensor


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