Diagnosing a Bad Crankshaft Position Sensor

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Car Repair How-To obd2

The Symptoms of a Bad Crankshaft Position Sensor

Modern car engines that are equipped with electronic fuel injection are fitted with crankshaft position sensors to properly monitor engine speed and the firing order of the combustion chamber. The crankshaft position sensor works in conjunction with other related sensors (such as the MAP or manifold pressure absolute and TPS/throttle position sensor) to produce a smooth running and well-conditioned engine.

The signals from the crank position sensor are utilized by the engine management system in the vehicle CPU to analyze and change specific parameters in regards to ignition and timing. This is the reason why symptoms of a bad crankshaft sensor produce engine vibration, misfires, and engine stalling.

Simply put, the crankshaft position sensor is an electronic device that monitors the rate at which the crankshaft is spinning. Like most electronic devices located in the engine compartment, the crank sensor (also known as the engine speed sensor) is relatively durable and designed to withstand extreme heat or other forces acting on the engine.

Why a Crankshaft Sensor Fails

Despite normal wear and tear caused by age, the crankshaft position sensor may fail due to the exposure of high temperature liquids or fluids coming from the engine. A gasket or crank problem may corrode the sensor unit with extremely hot coolant or engine oil and will burn out the sensor itself. This is why it’s important to fix any engine leaks as soon a possible so as not to cause harm among other engine components, including sensors and other vital electrical components.

Symptoms of a Bad Crankshaft Position Sensor

Understand the fact that the crankshaft position sensor is designed to enhance the following:

  • Emissions performance. The crank sensor is designed to constantly monitor clean emissions and an efficient combustion system.
  • Engine power.
  • Fuel efficiency.
  • Engine diagnostic capabilities.
  • Idling qualities (smooth and rattle free).

Any loss of performance related to the above mentioned factors may be the result of a bad crankshaft position sensor. This will include:

  • Inability to start the engine. If you keep cranking the engine and it won’t start, then you may have a bad crank sensor.
  • Rough idling or a hiccup during idling.
  • Engine misfiring.
  • Acceleration problems.
  • P0008 or P0016 OBD2 fault codes


Take note, however, that the above symptoms may present themselves in spite of a properly operational crank sensor system. It is then vital to have the system checked by a technician using an OBD-II scan tool to properly diagnose the problem.

Proper Diagnosis

A faulty or worn spark plug, dirty throttle body or misaligned throttle position sensor will also give the same symptoms as those of a faulty crank sensor. Mechanics and engine tuners are quick to point out that a slight hiccup at idle is a sure sign of a faulty crank position sensor, but this must be confirmed by the use of proper diagnostic equipment. This holds true when there is no check engine light on the console despite the presence of such symptoms.

A modern car is complex and the engine management system will vary according to car model and manufacturer. Not all automobiles behave the same way when it comes to engine management, but most will agree that ignition components should be checked first before replacing or removing engine sensors.

With the above stated symptoms present, it would be best to change or clean the spark plugs and throttle body first before confirming the diagnosis. Have the engine timing checked (for engines equipped with a distributor cap) for proper engine combustion.

If the vehicle fails to start, check the instrument panel for a presence of the check engine light to confirm a failed sensor or component. If the check engine light is lit, have a professional technician diagnose the system using a scanning tool to confirm if the crankshaft position sensor would need to be replaced.

If you want to save money, you can buy an OBD-II vehicle scanner like the Autel MaxiScan MS300 CAN Diagnostic Tool or the Innova 3150 Diagnostic Code Reader with ABS/SRS. These scanning tools are easy to use, and they’re not as expensive as, let’s say, sending your car to the dealership for repair. Of course, you may still need a mechanic to remove the faulty sensor (because some sensors are positioned in the funniest and most uncomfortable positions in the engine bay) but you’ll definitely save time and money in diagnosing the problem.


If your engine misfires during idle or hesitates upon acceleration, then have the system checked as soon as possible to avoid possible damage to other engine components. Follow the preventive maintenance procedures as stated in your owner’s manual to obtain years of smooth driving pleasure from your trusted automobile. Hopefully, you are now equipped to know the symptoms of a bad crankshaft position sensor.

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