What Is a Cam Position Sensor? CMP Explained [2026]

📖 What It Does

Identifies which cylinder is on its compression stroke so the ECU can sequence injectors and coils. Also enables VVT feedback - the ECU compares actual cam angle to commanded angle.

⚙ How It Works

A magnetic or Hall-effect sensor reads notches on a reluctor wheel attached to the camshaft. Each notch produces a voltage pulse. The pattern of pulses gives the ECU absolute cam angle. On VVT engines, that signal is read hundreds of times per second to control phasers.

⚠ Symptoms When It Fails

Symptoms include a no-start, hard start, stalling, hesitation, misfires, P0340-P0345 codes, and sometimes a temporary "no-spark" condition. Failures usually come from heat-degraded sensor electronics or oil contamination of the connector. See full symptom guide.

💰 Replacement Cost

Replacement: $150–$400. Sensors are $30–$150 in parts. Labor is 30–90 minutes for most engines. See CMP cost.

🔗 Related DTC Codes

❓ Frequently Asked Questions

Can a car run without a cam sensor?

Sometimes briefly, in "limp" mode using crank-only timing - but it will run badly.

What is the difference between cam and crank sensors?

Cam sensor identifies the engine cycle. Crank sensor tracks exact piston position. The ECU needs both.

Why does my car start, then die after a few seconds?

Often a failing CMP or CKP. The car starts on default and stalls when the bad reading is detected.

Does an oil leak kill cam sensors?

Yes - oil seeping into the connector corrodes pins. Fix the leak when you replace the sensor.

How long does a CMP last?

Often 100,000+ miles.

Can I drive with a P0340 code?

Yes but expect intermittent stalls. Replace soon.

What Is a Cam Position Sensor?