Camshaft Position Sensor Buyer's Guide
5 min read
RideBuilder
Camshaft Position Sensor Buyer's Guide
The camshaft position (CMP) sensor tracks the position and speed of the camshaft. It sends this data to the engine control unit (ECU), the computer that runs your engine. The ECU uses it to time fuel injection and ignition for each cylinder. Without a working CMP sensor, your engine will run poorly or may not start at all.
Most modern engines have one CMP sensor for each camshaft. For example, a four-cylinder engine with a single overhead cam (SOHC) has one camshaft and one CMP sensor. A V6 engine with dual overhead cams (DOHC) has four camshafts and can have up to four sensors. CMP sensors are usually mounted in the cylinder head or timing cover, near one end of the camshaft. When you replace a CMP sensor, choose one made for your exact vehicle and engine, or match the part number on your old sensor.
Failure Symptoms & Diagnostic Codes
The fastest way to diagnose a faulty CMP sensor is with an OBD-II scanner. Codes P0340–P0349 indicate a problem with the CMP sensor. Engines with separate sensors for the intake and exhaust camshafts also use codes P0365–P0369 and P0390–P0394. Codes P0010–P0025 point to the variable valve timing (VVT) system, which also relies on CMP data.
Common symptoms of a failing CMP sensor include:
- Long crank times
- Rough idle
- Engine stalling
- Check engine light
Pro Tip: Before replacing the sensor, inspect the wiring harness and connector for a loose or damaged connection.
Why Do Engines Need a CMP Sensor?
In a four-stroke engine, the crankshaft makes two full rotations per engine cycle. That means it passes through every position twice. The crankshaft position (CKP) sensor alone cannot tell the ECU whether a cylinder is on its compression stroke or its exhaust stroke. The crankshaft is in the same position for both.
The camshaft, by contrast, makes only one rotation per engine cycle. The CMP sensor signal tells the ECU which stroke each cylinder is on. The ECU can then fire the fuel injectors and spark plugs in the right order. Together, the CMP and CKP sensors give the ECU a complete, detailed picture of engine timing.
How CMP Sensors Work
Like the CKP sensor, the CMP sensor reads a toothed metal ring called a reluctor wheel. In this case, the wheel is mounted on the camshaft. As the camshaft rotates, the passing teeth and gaps change the magnetic field at the sensor tip. The sensor turns these changes into a pulsing electrical signal. The ECU uses that signal to calculate the camshaft's speed and position.
There are two types of CMP sensors: variable reluctance sensors and Hall effect sensors. Most modern vehicles use Hall effect sensors because they produce a clean signal even at low engine speeds. For a detailed explanation of how both types work, see our Crankshaft Position Sensor Buyer's Guide.
Variable Valve Timing
CMP sensors also make modern engine controls like variable valve timing (VVT) possible. In a VVT engine, the ECU adjusts the camshaft's timing relative to the crankshaft while the engine runs. This improves power and fuel economy and lowers emissions across different engine speeds and loads.
To make the adjustment, the VVT solenoid (also called an oil control valve) sends oil pressure to a cam phaser. The cam phaser then rotates the camshaft to the desired position. The CMP sensor reports the camshaft's actual position back to the ECU. The ECU uses this feedback to check and fine-tune the adjustment in real time. For a visual explanation of how VVT works, watch this video.
Conclusion
The CMP sensor works with the CKP sensor to give the ECU a complete picture of engine timing. That makes precise fuel injection, ignition, and VVT possible. If your OBD-II scanner shows a CMP fault code, check the sensor wiring and connector first. Look for damage or corrosion before you replace the sensor. For most vehicles, the right choice is a replacement that matches the original equipment manufacturer (OEM) part. Find a compatible CMP sensor and plan your build on RideBuilder.
