Introduction
This guide is designed for automotive professionals and enthusiasts who want to understand, diagnose, and troubleshoot the symptoms of a failing engine crankshaft position sensor.
Common Symptoms of a Failing CKP Sensor
- Illuminated Check Engine Light: The ECU may trigger diagnostic trouble codes (DTCs) like P0335 or P0336 indicating sensor circuit related malfunctions.
- Engine Stalling: A faulty sensor might cause the engine to stall unexpectedly, especially during idle or acceleration.
- Engine No Start: A "no spark" in the ignition system condition can be present when this sensor goes bad.
- Random Engine Misfires: When a crankshaft sensor becomes weak the waveform it produces can be jumbled which is difficult for the engine computer to decipher causing a misfire.
Sensor Failure With No Codes!
That's right! This sensor can fail and not have any codes, here is why:
If the engine is cranking and the computer does not see engine rotation, it will assume there is some kind of mechanical issue such as a broken crankshaft. Even thought the sensor is not working, the computer will not know this even though the engine will not start. This is because there are some things that can stop the crankshaft position sensor's signal that will have nothing to do with the sensor going bad, such as running out of gas, transmission operation problem, (converter clutch stuck on) or stalling the engine by letting the clutch pedal out too quickly.
Failure When Hot!
As with all sensors, heat can play a roll in their performance because of the thin wire windings which can expand with heat and short out to one another greatly changing the sensors resistance, stopping the signal to the engine computer. Once the sensor cools down, it can start working again, the most common failure for these sensors is when the engine is idling, it will just stall. This is because the pulse-width is at its widest at slower engine speeds.
Scanner Readings
It is easy to check if the crankshaft sensor is working using a scanner. Simply plug the scanner in and follow the prompts until you find "crankshaft revolutions" which should be at zero, then crank the engine over and it should give a reading of 120-300 RPM if the sensor is working, (cranking speed). Though you can test the sensors resistance using a voltmeter, the true way to test the sensor is to use an oscilloscope and check the waveform when the sensor is hot, the sign wave should be clean and clear.
False Codes
There is a common misconception that when you get the following codes you have a bad crankshaft sensor which can be sometimes not true:
P0337 – This indicates a “Crankshaft Position Sensor Circuit Low Input,” meaning
the sensor’s output voltage is lower than expected.
P0338 – This indicates a “Crankshaft Position Sensor Circuit High Input,” meaning
the sensor’s output voltage is higher than expected.
These codes are triggers by a reluctor wheel on the crankshaft that is out of time due to a mechanical issue such as a worn keyway on crankshaft, or loose reluctor wheel itself which will cause the sensor "peak" wave to be to early P0338 code or too late, P0337 code.
Visual Inspection
Carefully inspecting the sensor and its wiring, a visual check can reveal obvious physical damage or signs of wear that might affect sensor performance.
- Examine the sensor housing for cracks, chips, or damage.
- Inspect wiring and connectors for corrosion, fraying, or loose connections.
- Look for environmental contaminants like oil or coolant that might have infiltrated the sensor area.
Conclusion
This guide serves as a foundational resource for diagnosing the symptoms associated with a failing crankshaft position sensor. By employing modern diagnostic tools and adhering to established procedures, you can address sensor issues effectively.
Credits
This guide knowledge base was created by the 2CarPros Team, and by Ken Lavacot: Automobile repair shop owner and certified master automobile technician of over 30 years. If you have question or need help please ask one of our experts we are happy to help. Please visit our 2CarPros YouTube Channel.
Article published 2025-02-23
