Camshaft Position Sensor

What is a camshaft position sensor and where is it located?

Your vehicle’s camshaft position sensor—also known as a cam sensor, cam angle sensor (CAS), and sometimes even CMP sensor—is a key component to your engine's ignition timing system. It is typically used on vehicles equipped with direct ignition (distributorless). The camshaft position sensor is connected to the camshaft. As the camshaft rotates, the magnetic element inside of it rotates and creates a series of electrical pulses. The camshaft sensor detects these and gives a signal to the vehicle’s Electronic Control Module (ECM) or computer to let it know the position of the engine’s camshaft. Most cam sensors are hall effect or optical sensors, though some earlier versions were mechanical, driven by a gear similar to a distributor.

The camshaft (or camshafts, depending on your engine’s design) rotates to open and close the intake and exhaust valves in order to bring in the air/fuel mixture to the piston located within each engine cylinder in order for them to fire. Information about which valves are open (i.e. the postion of the camshaft and which piston/cylinder is being used) helps the computer activate the fuel injectors and spark plugs at the right time. This ensures the engine is running in the correct firing order and with good timing. 

Some engines may have two or more camshaft position sensors, one for each camshaft. Others may use only one sensor regardless of the number of camshafts. The camshaft sensor is usually located at either end of the engine cylinder head.

How do I know if my cam sensor needs to be replaced?

Since the cam position sensor’s role is to supply information for the engine’s timing and firing systems, failure of the sensor can lead to problems with these systems. Without knowing which valves are open or exactly when they are opening and closing, the computer cannot operate the fuel injectors and spark plugs at the right time. This can lead to all kinds of engine trouble. 

For example, the engine may misfire, sputter, or run roughly. It may also struggle to accelerate or stall during acceleration. The engine may also take longer to start, especially under cold conditions. In the worst case scenario, the computer may not activate the fuel injectors at all and the car simply will not start. If the problem reaches that point, a replacement camshaft sensor will be strictly necessary. 

Before it gets to that point, though, your check engine light will likely come on. For camshaft sensor problems, a diagnostic scan tool will show codes between P0340 and P0349, shown below.

OBDII Check Engine Codes related to Camshaft Position Sensors

P0340 Camshaft Position Sensor Circuit Malfunction
P0341 Camshaft Position Sensor Circuit Range/Performance
P0342 Camshaft Position Sensor Circuit Low Input
P0343 Camshaft Position Sensor Circuit High Input
P0344 Camshaft Position Sensor Circuit Intermittent
P0345 Camshaft Position Sensor A Circuit Malfunction (Bank 2)
P0346 Camshaft Position Sensor A Circuit Range/Performance (Bank 2)
P0347 Camshaft Position Sensor A Circuit Low Input (Bank 2)
P0348 Camshaft Position Sensor A Circuit High Input (Bank 2)
P0349 Camshaft Position Sensor A Circuit Intermittent (Bank 2)

Can I replace a camshaft sensor myself?

The difficulty of replacing a CMP sensor will vary with the design of your engine and the location of the sensor. Removing and installing the sensor itself will not prove too difficult—it usually just requires the removal of a bolt or two. You may have to remove other parts, such as air intake components, serpentine belt, exhuast manifold, timing cover, etc. to access the sensor. This, of course, makes the job more labor intensive, so it's important to find the location of your sensor to determine how time consuming and difficult the job may be.