The camshaft position sensor tells the engine computer where the camshaft is, so it knows which cylinder is on its compression stroke for spark and fuel timing. On engines with variable valve timing it also reports the actual cam angle so the computer can control the cam phasers. A failing camshaft position sensor causes hard starting, stalling, rough running and codes such as P0340.
Bad camshaft position sensor symptoms
- Hard starting or long cranking before the engine fires
- Stalling, often when hot, and restarting after it cools
- Rough running, misfires or a stumble
- Reduced power or a check engine light
- Erratic shifting on some vehicles that use the cam signal for shift timing
Camshaft position sensor codes
| Code | Meaning |
|---|---|
| P0340 | Sensor A circuit, bank 1 or single sensor |
| P0341 | Sensor A range/performance |
| P0345 | Sensor A circuit, bank 2 |
| P0365 | Sensor B circuit, bank 1 (usually the exhaust cam) |
| P0016, P0018 | Crank and cam signals out of correlation |
Where is the camshaft position sensor?
Location depends on the engine. Overhead cam engines usually mount it on the cylinder head or valve cover near the end of a camshaft, and dual-cam V engines can have up to four. Pushrod V8s often mount it on the front timing cover; on early GM LS engines it sits at the rear of the block behind the intake manifold, while later LS engines moved it to the front cover. Your service information shows the exact position.
Cam sensor vs crank sensor
Both sensors read a toothed wheel. The crankshaft sensor gives engine speed and piston position and is essential: without it most engines will not run. The cam sensor identifies the stroke; many engines can still start without it, just with longer cranking. See crankshaft and camshaft position sensor symptoms and P0335 for the crank side.
How to test a camshaft position sensor
- Read codes and watch the cam signal or sync status on a scan tool while cranking.
- Check the connector for oil contamination, which is common when valve cover or front cover seals leak.
- Three-wire Hall-effect sensors need a reference voltage and ground; check both at the connector.
- On V engines with identical sensors, swap bank 1 and bank 2 sensors and see whether the code moves.
- A scope shows dropouts that a meter misses, especially when the engine is hot.
When it is not the sensor
If a new sensor does not fix correlation codes, the camshaft timing itself may be off from a stretched chain, a worn guide or a cam phaser problem; see timing chain symptoms and VVT solenoid. A chain that has jumped time can damage valves, and if the engine is badly damaged our engines page lists replacements by code.
More guides: what does a camshaft do? · bad cam phaser symptoms.
Trouble codes: P0366 Cam Sensor B Range/Performance · P0344 Cam Sensor A Intermittent · P0369 Cam Sensor B Intermittent · P0342 Cam Sensor A Circuit Low · P0343 Cam Sensor A Circuit High · P0346 Cam Sensor A Range Bank 2 · P0347 Cam Sensor A Low Bank 2 · all OBD2 codes.
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