What is a Camshaft Position Sensor?
Tracks the camshaft so the ECU knows which stroke each cylinder is on.
Simplified animation — not to scale.
In plain English
A Hall-effect sensor near the camshaft that signals when a reference tooth passes, allowing the ECU to identify the firing order and time fuel injection precisely.
"If the crank sensor counts the beats, the cam sensor tells the engine which verse of the song it's on."
How it works
The camshaft turns at half crank speed and opens and closes the valves. The sensor watches a single reference tooth on the cam and produces one pulse per cam revolution. Combined with the crankshaft sensor, the ECU now knows not just where the pistons are but whether each cylinder is on its intake, compression, power or exhaust stroke. This enables sequential fuel injection and coil-on-plug ignition, both of which improve efficiency and emissions.
Signs of trouble
- ⚠Long crank times before starting
- ⚠Check engine light (P0340)
- ⚠Stalling at idle
- ⚠Reduced fuel economy
£50–£200
Always get a written quote. Prices vary by car, region, and parts brand.