Symptoms of a Bad Camshaft Position Sensor

Mia Bevacqua
June 13, 2018

The camshaft position sensor, or CMP sensor, is one key to a healthy engine. When this sensor goes bad, it can cause all sorts of engine trouble and even put drivers in danger. Here are some common symptoms:

1. Your engine isn’t running well: The signal from this sensor is required to operate the fuel injectors, as well as most timing-based engine functions, like spark control. Because of this, a faulty sensor can easily cause a misfire, poor acceleration or other problems. The most dangerous scenario would likely be that the sensor fails while you’re driving on the freeway and causes your speed to drop or your engine to quit without warning.

2. Your check engine light is on: If the car’s computer detects a problem with the camshaft position sensor, or its circuit, it will turn on the check engine light.

3. Your engine stalls: An intermittent or faulty signal from the sensor can rob the engine of spark or fuel, causing it to stall. This can also result in the car’s computer going into “limp-home mode,” meaning only a couple of gears will be available, forcing you to drive relatively slowly. If this happens, get your car to a mechanic immediately.

4. Your car won’t start: If the computer isn’t getting a signal from the camshaft position sensor, and cannot use another signal instead, it won’t turn on the fuel injectors or fire the ignition. This results in an engine that cranks but doesn’t start. If the signal disappears while you’re driving, the car may die out instead.

Get it diagnosed by a professional

What is the camshaft position sensor?

The camshaft is one of the main shafts inside your car’s engine. Its primary responsibilities are to open and close the engine valves, allowing airflow in and out of the combustion chamber, where power is produced. Depending on the design of the engine, there may be one or more camshafts, as well as one or, on rare occasions, two crankshafts

The opening and closing of the valves needs to be timed perfectly against the movement of the pistons in the cylinders. If this timing gets thrown off, your engine power, economy and emissions will suffer. This is why camshaft position sensor data is critical to the engine’s computer.

Most engines made in the last couple decades use one or more camshaft position sensors to measure the speed and position of the camshaft or camshafts. The engine’s computer uses this information to run the fuel injectors. In addition, the sensor may be used for other functions, like variable valve timing and ignition system operation.

» LEARN MORE: Get an estimate for a new camshaft position sensor

How to fix the problem

If you’re noticing any of the above problems, make sure to get your car diagnosed by a mechanic before replacing the camshaft position sensor. There are a number of causes for these kinds of symptoms, so it’s helpful to narrow things down before throwing money at the problem.

A faulty camshaft position sensor should be replaced. To protect the camshaft position sensor, it’s often put in difficult to access locations like deep within the engine or between the engine and transmission. Other times it might be located conveniently near the top or front of an engine. Labor prices will vary, even on the same engine in different model vehicles. 


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.

2 User Comments

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By , June 06, 2010
I replaced the camshift sensor in my 2003 Dodge SXT and its located next to the starter
By , August 12, 2017
I have a 2010 malibu lt and check engine light is on said cam/crankshaft position sensors need to be replaced. So I did, cleared codes, and engine light keeps coming back on.

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