Symptoms of a Bad Crankshaft Position Sensor

Mia Bevacqua
May 15, 2018

A faulty crankshaft sensor can cause several problems, and even prevent your car from starting:

1. The check engine light comes on: The engine’s computer monitors crankshaft position sensor operation. If it detects a problem with the sensor, or its circuit, it will turn on the check engine light

2. The tachometer doesn’t work right: The computer receives information about engine speed from the crankshaft position sensor. It then relays that information to the tachometer on your dash. A faulty sensor can result in the tachometer not working, or working erratically.  

3. Your fuel economy suffers: If the crankshaft position sensor isn’t working right, your fuel injection won’t work as efficiently. Your gas mileage will suffer as a result.

4. The engine won’t start: The engine’s computer relies on information from crankshaft position sensor for ignition system control. The computer won’t provide the engine with spark without a crankshaft position sensor signal. This will result in an engine that cranks but doesn’t start

5. The engine runs rough or stalls: The crankshaft position sensor signal is also used to determine ignition timing. Because of this, a faulty sensor can easily cause a misfire and poor engine performance. It can even rob the engine of spark, causing it to stall

Get it diagnosed by a professional

What is the crankshaft position sensor?

The crankshaft position sensor plays a big role in making sure your engine runs smoothly.

There are two primary shafts inside the engine — the crankshaft and camshaft. The crankshaft is connected to the bottom of the pistons and rotates as they move downward after combustion. It sends this power to the transmission, allowing your car to move.

The crankshaft position sensor measures the speed and position of the crankshaft as it rotates. The car’s computer then uses the sensor’s signal to decide when to fire the spark plugs, thus determining ignition timing. The signal from the crankshaft position sensor may also dictate functions such as variable valve timing, fuel injection and tachometer operation. 

» GET AN ESTIMATE: See how much your crankshaft position sensor replacement may cost

How to fix the problem

Before replacing the crankshaft position sensor, a thorough diagnosis should be performed. A professional mechanic can do this using equipment such as a scan tool, digital multimeter and oscilloscope. 

A faulty crankshaft position sensor should be replaced. Typically, the sensor is only held in place by one or two fasteners and is relatively easy to swap out. The sensor is most commonly found behind the crankshaft pulley or under the timing cover.

On some vehicles, though, it’s buried deep inside the engine compartment. This makes getting to it very challenging, and should be handled by a professional mechanic. 


Mia Bevacqua

About the Author

Mia Bevacqua is an automotive expert with ASE Master, L1, L2 and L3 Advanced Level Specialist certification. With 13-plus years of experience in the field, she applies her skills toward writing, consulting and automotive software engineering.

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