Carautonomy — car parts and warning lights explained
Follow
Home
NewDiagnose my car
Articles
MOT Checker
About
Survey
← All car parts
Sensors

What is a Camshaft Position Sensor?

Tracks the camshaft so the ECU knows which stroke each cylinder is on.

CAM POSITION / PHASE REFERENCESYNCVIEWED ALONG SHAFT AXISHALL SENSORAIR GAPSIGNAL OUTPUT5 VONE PULSE / CAM REVOLUTIONReference tooth passes sensor → ECU identifies cylinder phase

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.

A simple analogy

"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
Rough UK cost

£50–£200

Parts: £20–£80
Labour: £30–£120

Always get a written quote. Prices vary by car, region, and parts brand.

Heads up: Carautonomy is for general guidance only. If your car is showing warning lights or behaving oddly, get it looked at by a qualified mechanic.

Keep exploring

Alternator
The on-board power station that keeps your battery topped up.
EGR Valve
A small valve that recycles exhaust gas to reduce emissions.
Starter Motor
The muscle that turns your engine over when you twist the key.

Find this article useful?

Be first to read new articles directly to your inbox.

*We'll only use your email to send you new articles and updates from carautonomy — nothing else, no third parties. You'll get a confirmation email to verify your subscription, and you can unsubscribe any time.

Carautonomy — car parts and warning lights explained

Helping the UK understand how their cars actually work — one car part at a time.

Explore
  • All car parts
  • Maintenance checks
  • Warning Lights
  • Features Explained
  • EV Transition
  • EV Reality Check
  • About the project
  • Contact us
  • Privacy Policy
Autonomy family
  • Moto Autonomy
  • Bike Autonomy
  • Camper Autonomy
  • More vehicle types coming soon
A friendly note

Information here is general guidance, not a diagnosis. Always speak to a qualified mechanic before parting with cash.

© 2026 Carautonomy