What Happens If You Don’t Relearn Crankshaft Position Sensor?

If you change your vehicle’s crankshaft position sensor, the first thing you should do is relearn the sensor. Otherwise, the sensor might provide wrong information about the crankshaft location, affecting your engine performance. 

Also, sometimes your vehicle will not start if you do not relearn the crankshaft position sensor. So, relearning is necessary if you change your vehicle crankshaft position sensor and other engine components. 

In the article, I will explain what happens if you don’t relearn the crankshaft position sensor. Also, I will provide a step-by-step guide that helps you to relearn the sensor.

What is Crankshaft Relearning?

Relearning refers to re-engineer, re-program, or re-calibrate the engine. If the crankshaft position sensor, engine, or timing cover is moved, removed, replaced, or disturbed, then the crankshaft position sensor needs to be relearned.

It is necessary to relearn the sensor to synchronize it with the crankshaft. The PCM uses this data for several purposes, such as determining ignition timing, identifying cylinder misfires, timing fuel injectors, etc. The engine may still run without relearning, but the PCM will use the incorrect “sync” data from the last relearn.

What happens if you don’t relearn crankshaft position sensor?

The ECU uses the signal from the position sensor to calculate engine speed and ensure the spark plug fires at the right moment. So, if you don’t relearn the crankshaft position sensor, the ignition system will fail to operate correctly. 

Here are listed some common problems that happen with your vehicle if you don’t relearn crankshaft position sensor:

Engine won’t start

Without relearning, the ECU sometimes doesn’t get the accurate location of the crankshaft and engine speed. The ignition will not maintain the correct timing of spark plug fires, which can affect the vehicle’s regular operation. The engine will not be able to start because of this obstacle.

Engine will overheat

The crankshaft position sensor maintains the temperature of the engine and engine components. But, if you don’t relearn the system, the sensors will send misleading information about crankshaft rotation, which is excessive build-up. For this, the engine will face an overheating issue.

Engine misfire

You will notice an engine misfire if you do not relearn the crankshaft position sensor, as the sensor sends the ECU incorrect information. A misfire in your engine may cause it to stumble or even lose speed (RPMs).

Rough acceleration

If your vehicle doesn’t get the proper information from the crankshaft position sensor, it cannot be able to adjust the spark timing or fuel injection. For this, your vehicle will face difficulty with a constant speed vehicle accelerating. You will notice uneven or rough acceleration.

Increase fuel consumption

The ECU and crankshaft position sensor work together to manage fuel injection. ECUs can inject too much or too little fuel if they receive inaccurate crankshaft location information. This will affect fuel efficiency. Also, it will increase the emission.

Advantage of relearning the crankshaft position sensor

After relearning the sensor, you will have a pleasant experience while driving your car. The relearn process ensures that ECU gets a proper signal from the crankshaft, which means no misfire, rough acceleration, and many more. 

You can enjoy the ride rather than thinking about stalling at the roadside. Also, this help to remove any remaining code that might cause your headache. 

How to relearn crankshaft position Sensor?

A crankshaft position sensor’s relearn procedure varies slightly according to the car’s model and make. But, you can follow the steps below to relearn the sensor applicable to almost all GMC vehicles.

Relearning Crankshaft Position Sensor Using scanner

Step 1: First, turn on your vehicle’s ignition without starting the engine. This will help the scanner tool get the information from your vehicle properly.

Step 2: Now, connect an OBD2 scanner tool with your vehicle. For most vehicles, the OBD2 port is located near the front door of the driver’s seat.

Step 3: Select your vehicle type and model. Also, you can use the auto-detect option, which asks for your VIN. Put the VIN number, and it will collect the vehicle information.

Step 4: Go to the “Diagnose” function and then “control Unit.” In the next window, you will get different parts options of the vehicle. You need to go to the “Powertrain.” Then, select the “ECM – Engine Control Module.” 

Step 5: On the next window, you will get the “Special Function” option. Then go to the “Cam crank relearn.” Then the information tab will open, which informs you when you should relearn the crankshaft position sensor. 

Step 6: The scanner will ask you to turn on the engine. Then, turn on the engine. At this moment, your vehicle coolant temperature should be 70 degrees Celsius. Otherwise, you cannot perform the relearn process.

Step 7: If the required temperature reaches, it will show it’s in progress now. After completing the relearn process, it will show you the complete message on the scanner tool.

NOTE: If the scanner tool detects other error codes, you must first clear them. Otherwise, the relearn procedure cannot be done.

Relearning Crankshaft Position Sensor Without Scanner Tool

Some vehicle models (some truck applications 1998 & later) relearn processes that cannot be done by a scanner tool. For this, you need to follow the manual method. Here is a step-by-step process of how you can relearn the sensor without a scanner tool:

  • Turn off the vehicle’s other accessories and check the air and coolant temperature. 
  • Now, turn on the engine and keep it in the park or neutral mode for 2 minutes. 
  • To reach operating temperature, accelerate to 55 mph on part throttle. Then, cruise for 8-10 minutes at this speed.
  • Continue cruising at 55 mph for another 5 to 6 minutes.
  • Decrease the vehicle to 45 mph without pressing the brake pedal. Release the feet from the accelerator pedal and wait for one minute at this speed.
  • You need to perform four 25-second deceleration cycles at a speed of your choice, followed by 15 seconds of 45 mph. You should not step on the brake during this procedure.
  • Then again, speed up to 55 mph and maintain the speed for two minutes.
  • With the clutch pressed and the brake applied, stop the vehicle and idle it for two minutes.

NOTE: If your vehicle has poor scanner support, you can follow the above method. However, it will be a good decision to contact a professional if you cannot perform the relearn process using a scanner tool.


Do crankshaft sensors need to be relearned?

Yes, you need to relearn the crankshaft position sensor whenever you change the engine or engine component. You need to do the process to ensure the proper functionality of the crankshaft after changing parts. 

Also, If you replaced the vehicle ECU, you need to relearn the sensor for appropriate communication with the new ECU.

Will disconnecting the battery reset the crankshaft sensor?

Removing the battery negative terminal for an hour can drain any remaining power or error code. But, most vehicles cannot reset the crankshaft position sensor. 

You need to use a scanner tool to reset the crankshaft sensor. But, it will help to remove any remaining store code on the crankshaft position sensor.

How long does it take to relearn?

Anyone can do the relearn process if they own a good quality OBD2 scanner tool. The procedure is so easy, and you don’t need to have any mechanical knowledge to perform the task. The relearn procedure will not take more than 10 minutes.

How much does it cost to relearn from a mechanic?

The cost will vary according to your location and vehicle model. But, as the relearn process doesn’t require any extra parts except a scanner tool that a mechanic already owns, the mechanic will take only the labor cost. The cost will be no more than $50.


Relearn process is required if you change your engine or crankshaft position sensor. You will notice several vehicle issues if you drive the car without relearning. 

I hope you know what will happen if you don’t relearn the crankshaft position sensor. Also, relearn process guide will help you to do the procedure without any issues.

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