What Is a Camshaft Position Sensor And What Does It Do?

by Jignesh Sabhadiya

Your car has many different sensors, including one or more camshaft position sensors. Although camshaft position sensors are designed to last the life of the vehicle, that doesn’t always happen.

Over time, these sensors can degrade to the point that they produce an erratic signal or no signal at all.

If your car experiences a camshaft position sensor failure, you’ll likely notice one or more troubling symptoms that you’ll want to address right away.

What is A Camshaft position sensor?

Camshaft position sensors monitor the camshaft’s position and send information to the engine control unit about when each valve is open on a particular cylinder. They work closely with crankshaft position sensors to paint a complete picture for the engine control unit.

The engine control unit needs this data to control how much fuel enters the combustion chamber and ignition timing (spark timing) to ignite the fuel, when the air-fuel mixture is ignited simultaneously, engine performance increases, fuel consumption, and tailpipe emissions decrease.

In modern auto-start/auto-stop engines, the camshaft position sensor determines which cylinder is on its power stroke relative to the crankshaft position and provides fuel and spark to start the engine when you step on the accelerator pedal.

A defective camshaft position sensor can warn you before it fails and leaves you stuck.

Key Summary

• The camshaft position (CMP) sensor monitors the speed and position of the camshafts. The powertrain control module (PCM) also uses the information from this sensor to calculate valve timing and watch out for misfires.
• An illuminated check engine light, engine performance issues, and hard starting are the telltale signs of a bad camshaft position sensor.
• It can cost anywhere between $100 and $300 to replace a faulty camshaft position sensor.

How Many Camshaft Position Sensors Are in a Car?

A vehicle may have one or more of these sensing devices. There’s usually one cam sensor in the engine. However, some have more than one and up to four.

In principle, vehicles without variable valve timing (VVT) have one, while those with VVT have two or four. Most have two, though. Four are rare to find.

Older engines that use a carburetor system have none. In these vehicles, there’s no need for TDC determination. They include those made in the 90’s or earlier.

Where is the Camshaft Sensor Located?

The exact location varies from one engine or vehicle to another. Most modern engines have it mounted at the top near the camshaft. In some, you can find it in the engine block or other components such as the flywheel or transmission bell.

That said, you can always use your car’s manual to find the exact location of this sensing device. Knowing its location can help you check it for damage, and if you’re a DIY enthusiast, replace it if it fails.

bad camshaft position sensor symptoms

Usually, there are a few warning signs that you may experience when the camshaft position sensor is failing. Keep an eye out for these common symptoms:

• Poor Fuel Economy: A failing camshaft position sensor will provide inaccurate data to the engine control module. With the wrong information, your engine will not be able to run as efficiently as it should causing it to consume more fuel.
• Stalling: When the fuel injectors are not delivering the proper amount of fuel, the engine could experience stalling.
• Engine Idles Roughly: A rough idling engine could be caused by a failing camshaft position sensor. This issue is more evident when the engine is idling.
• Hesitation: Hesitation during acceleration is a common issue that you may experience with a bad camshaft sensor.
• Failed Emissions Test: When the engine is not performing properly, it will not be able to burn fuel efficiently. This can lead to increased emissions.
• Smell of Gas: Unburned fuel can make its way out of your tailpipe which can produce a noticeable smell of gas.
• Car Will Not Start: Over time, as the camshaft position sensor fails, the signal it sends to the engine control module weakens. When the engine no longer receives the signal, you will not be able to start your car.
• Engine Misfires: A failing camshaft position sensor can cause your engine to misfire.
• Transmission Shifting Problems: The data sent to the engine control module can stop the transmission from shifting properly. In some vehicles, there is a security feature that puts the car in “limp mode.” This helps to prevent major engine damage.
• Check Engine Light is Illuminated: When your vehicle is experiencing a problem, it will trigger the check engine light. The light can be triggered by a number of different reasons. If your warning light is lit on your dashboard, have your mechanic run a diagnostic scan as soon as possible to determine the exact problem. If the light is flashing, stop as soon as it is safe and turn your car off. Call for a tow. Do not continue driving your vehicle.