This bisected four-cylinder inline engine in an MG automobile contains a crankshaft and crankshaft position sensor.

Crankshaft Position Sensor: Overview and Troubleshooting

A crankshaft position sensor is part of your car’s electronic fuel injection and ignition system. Found in modern cars, this sensor measures the engine’s revolutions per minute (RPM) as well as the exact position of the engine crankshaft. When this sensor fails, the engine won’t turn over, and you won’t be going anywhere until it is fixed.

The crankshaft position sensor is sometimes referred to as an engine speed sensor. It looks like a long, black plug and is located near the crankshaft. When it does its job, it ensures the required RPM value for the appropriate transmission gear. The following are key signs that this sensor is no longer doing its job.

1. Drop in Fuel Efficiency

When the sensor isn’t working correctly, it’ll have a negative impact on fuel economy. You may notice you’re making more frequent trips to the pump, especially if your driving habits remain constant. As long as all other factors about your vehicle are unchanged — namely that there are no due maintenance items — this sensor may very well be the culprit.crankshaft position sensor

2. Poor Acceleration

Before the crankshaft sensor fails completely, you may notice some hesitation while accelerating. Here, the sensor isn’t sending the correct information to your car’s computer, which, in turn, won’t accurately synchronize the engine’s pistons. Expect your vehicle to have difficulty maintaining its speed with a faulty crankshaft position sensor, as well.

3. Engine Misfiring and Stalling

A faulty crankshaft sensor will cause your engine to misfire as incorrect fuel injection readings weigh in. When this problem becomes especially apparent, the engine may stall and have difficulty restarting. Rough idling and backfiring are two more indicators that something is wrong. If the engine fails to start, the sensor has likely worn out.

4. Check Engine Light

When the check engine light glows, that’s always a sign of a problem. Consider it an additional warning that the crankshaft sensor is failing, especially when coupled with a drop in fuel efficiency, poor acceleration or engine misfiring or stalling. An engine light diagnostic tool can pinpoint the problem, enabling you to take the appropriate action.

The bottom line here is to never neglect engine problems. If you do, you may face far worse issues down the road. Fortunately, the crankshaft sensor is usually easy to remove, with just a few bolts and wires holding it in place. Replacing it should be a quick job for you or your local NAPA AutoCare, and taking care of it as soon as you notice the problem will keep your engine safe.

Check out all the relays, sensors and switches available on NAPA Online or trust one of our 16,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on the crankshaft position sensor, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Flickr.

about author

Matthew C. Keegan

Matt Keegan has maintained his love for cars ever since his father taught him kicking tires can be one way to uncover a problem with a vehicle’s suspension system. He since moved on to learn a few things about coefficient of drag, G-forces, toe-heel shifting, and how to work the crazy infotainment system in some random weekly driver. Matt is a member of the Washington Automotive Press Association and is a contributor to various print and online media sources.

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