Troubleshooting Problems After Replacing Your Crankshaft Sensor

troubleshooting problems after replacing your crankshaft sensor

Having problems with your car after replacing the crankshaft sensor? Issues like the engine not starting or running roughly are frustrating and concerning, but they can often be resolved with some troubleshooting and resetting procedures. This post will walk through the key steps to take after replacing your crankshaft sensor to get your car running smoothly again.

Why Do You Need to Replace the Crankshaft Sensor in the First Place?

Before jumping into the post-replacement troubleshooting, let’s briefly go over why you may have needed to replace the crankshaft sensor (also known as the crank position sensor) to begin with.

What Does the Crankshaft Sensor Do?

The crankshaft sensor is an important engine management component that monitors the position and speed of the crankshaft. It sends critical signals to the powertrain control module (PCM) to allow proper fuel injection and ignition timing.

Symptoms of a Failing Crankshaft Sensor

Some common signs that your crankshaft sensor is wearing out or faulty:

  • Difficulty starting the engine or engine not turning over
  • Stalling, rough idle, hesitation
  • Check engine light with error codes related to crankshaft position
  • Engine misfires or lack of power

If you had any of those crankshaft sensor failure symptoms, then replacing it was the right fix. But you still need to address any post-replacement problems to get your car running optimally again.

Step-by-Step Crankshaft Sensor Replacement

Before getting into the resetting and relearning steps, let’s briefly review the replacement process itself.

Locating the Crankshaft Sensor

  • The crankshaft sensor is typically located on the front of the engine block, near the main pulleys and belts.
  • Consult your vehicle repair manual for the exact location if you have trouble finding it.

Removing the Old Sensor

  • Disconnect the car battery ground cable before starting work.
  • Unplug the electrical connector from the old sensor.
  • Remove the mounting bolts securing the sensor.
  • Detach the old sensor from the engine block.

Installing the New Sensor

  • Clean any dirt or debris from the sensor mounting area on the block.
  • Apply threadlocker to the new sensor’s mounting bolts.
  • Position the new sensor and hand-tighten the bolts.
  • Reconnect the electrical connector.
  • Reattach the battery ground cable when finished.

Those are the basics for the physical crankshaft sensor replacement itself. But the job isn’t complete until you also address the resetting and relearning steps outlined next.

Common Problems After Crankshaft Sensor Replacement

After installing a new crankshaft sensor, you may run into some of these potential issues:

Engine Won’t Crank or Start

If the engine won’t turn over or crank at all after replacing the sensor, there are a few things to check:

  • Verify proper electrical connections – Make sure the new sensor connector is fully seated and locked. Check for damage.
  • Inspect sensor installation – Confirm correct positioning and that no mounting bolts are missing or loose.
  • Battery condition – A weak battery unable to provide sufficient amps may prevent cranking.

Rough Idle, Stalling, Hesitation

The crankshaft sensor replacement procedure requires “relearning” the position. Until that’s completed, you may experience:

  • Rough or fluctuating idle – The engine RPM may surge up and down at idle.
  • Stalling, dying – Engine may stall randomly, especially right after starting.
  • Hesitation, lack of power – Lag or flat spot during acceleration.

These symptoms should resolve after the resetting process is finished.

Persistent Check Engine Light

If the check engine light remains on after replacing the crankshaft sensor, it could indicate:

  • Incorrect installation – Faulty sensor or improper positioning may trigger error codes.
  • Unrelated issues – Existing problems with fuel, ignition, etc. systems.
  • Incomplete relearn procedure – Crank position not yet fully relearned by PCM.

Carefully follow the relearning steps outlined next. If the light remains on, further diagnosis may be needed.

Resetting and Relearning Crankshaft Position

The most critical part of the sensor replacement process is resetting the engine control module (ECM) and allowing it to relearn the new crankshaft’s position. Here is how to do it properly:

Options for Resetting the ECU

There are a couple methods for resetting the engine control unit after sensor replacement:

  • Battery Disconnect – Disconnect the negative battery cable for 30 minutes or more. This erases stored codes and data allowing relearning.
  • Scan Tool Reset – A diagnostic scan tool can also be used to reset the ECM if available.

The battery disconnect method can be done easily at home. The scan tool reset requires professional equipment but is more thorough.

Performing the Crankshaft Position Relearn Procedure

After resetting the ECU, the relearning procedure should be followed:

  • Start the engine and let it reach full operating temperature.
  • Allow it to idle for 10-15 minutes.
  • Drive the vehicle for 10-15 minutes under a variety of driving conditions.

This allows the PCM to fully learn the signals from the new crankshaft sensor and adapt for proper ignition timing and fuel delivery.

Number of Drive Cycles Needed

The relearn may take multiple drive cycles to complete fully. It is normal for symptoms like rough idle or hesitation to persist through the first few drive cycles as it adjusts. Several days of normal driving may be needed for the best results.

Be patient and allow the ECU time to relearn if any lingering symptoms are present after sensor replacement.

Verifying Correct Installation of New Sensor

Before assuming relearning alone will resolve any problems, check for proper mechanical installation of the new crankshaft sensor:

Check Connectors and Wiring

  • Inspect sensor harness and make sure no wires are damaged or corroded.
  • Verify a tight fit when connecting electrical plugs. Loose or faulty connections will cause issues.

Confirm Correct Mounting and Position

  • Ensure no looseness where sensor mounts to engine block.
  • Check that alignment looks correct when compared to old sensor.
  • Consult a repair manual if unsure – incorrect position will prevent relearning.

Use a Scan Tool to View Crankshaft Sensor Data

  • With a connected scan tool, look for related sensor parameter IDs:
    • Crankshaft position sensor voltage
    • Crankshaft position variation learn
    • Crankshaft reference position learned
  • Monitor for expected voltage and proper operation.

This can identify sensor failures and installation faults missed through visual inspection alone.

Multimeter Testing If Needed

For advanced testing, a multimeter can be used to test wiring continuity, resistance, reference voltage at the sensor connector. This helps verify electrical integrity and proper sensor function.

Ruling Out Other Potential Causes

While crankshaft sensor replacement and relearning may fix your issues, also consider other related systems:

Camshaft Position Sensor

  • Dual cam and crank sensors are used on some vehicles. Make sure the cam sensor was not also faulty.

Mass Airflow Sensor

  • Skewed MAF sensor data could confuse the ECU when combined with new crankshaft position data.

Ignition System Parts

  • Faulty spark plugs, plug wires, ignition coils can cause misfires and driveability problems resembling crank sensor issues.

Fuel Pressure and Pump

  • Weak fuel pump or filter may be unable to supply adequate fuel pressure, causing hard starting or stalling.

Check for trouble codes, symptoms pointing to these other potential sources if driveability problems continue after replacing the crankshaft sensor.

When to Take Your Vehicle to the Mechanic?

While many can tackle crankshaft position sensor replacement and troubleshooting themselves, see a professional mechanic if:

  • You don’t feel comfortable performing electrical testing or disconnecting the battery yourself.
  • Driveability problems persist after thorough DIY troubleshooting.
  • You need a scan tool to access sensor data or reset ECU.
  • The check engine light remains on indicating unresolved issues.
  • Timing belt service is also due – have it inspected/replaced when doing sensor replacement.

Repair shops have advanced diagnostic tools to identity lingering electrical or sensor faults. They can also confirm that related systems like the timing belt are in good working order after your sensor replacement.

FAQ – Common Crankshaft Sensor Replacement Questions

Do I Really Need a Scan Tool to Reset and Relearn?

No, a basic battery reset and relearn procedure can be done without a scan tool. But a professional grade scan tool allows more thorough relearning and the ability to view live sensor data.

How Long Does the Relearn Process Take?

Expect at least 10-15 minutes of idle time after a restart. Then driving cycles over a few days will likely be needed for the PCM to fully relearn positions. Extended rough running or symptoms while this completes is normal.

Could a Brand New Sensor Be Bad?

It’s unlikely, but yes – an out of the box faulty crankshaft position sensor could cause continued issues after replacement. Confirm proper installation first, but replace again if needed. Look for authentic OEM sensors from reputable suppliers.


While the replacement itself is straightforward, resetting the ECU and allowing full relearning of the crankshaft position is vital for smooth operation after installing a new crankshaft sensor. Following the battery disconnect or scan tool reset procedures outlined and allowing adequate drive cycles will avoid prolonged problems. Verify proper sensor installation as well during troubleshooting.

With attention to these post-replacement steps, your car will be back to running great. The crankshaft sensor replacement will be a solution instead of just the start of new headaches.

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