The crankshaft position sensor tells the engine computer exactly where the crankshaft is and how fast it is turning, which it needs to time the spark and fuel injection. When it fails, the engine may crank but not start, stall without warning, especially when hot, or misfire; the tachometer may drop to zero while the engine is running. The camshaft position sensor works with it to identify which stroke each cylinder is on.
How the sensors work
- Crankshaft position sensor: reads a toothed reluctor wheel on the crankshaft or flexplate; the pattern of teeth gives position and speed.
- Camshaft position sensor: reads a target on the camshaft so the computer knows which cylinder is on its compression stroke, which sequential fuel injection and coil-on-plug ignition need.
Bad crankshaft position sensor symptoms
- Cranks but will not start
- Stalling, often when the engine is hot, then restarting after it cools
- Misfires, rough running or hesitation; see engine misfire
- A tachometer that drops or flickers
- Check engine light with crankshaft sensor codes such as P0335
Camshaft position sensor symptoms
- Hard starting or long cranking
- Rough running, stalling or a reduced-power mode
- Codes such as P0340 for the cam sensor circuit, or P0016 for cam and crank correlation, which can also point to a stretched timing chain; see timing chain symptoms
Testing and replacement
Scan data showing engine speed while cranking is a quick check: no RPM signal while the engine turns points to the crank sensor or its wiring. Inspect connectors for oil contamination and damage, and check the wiring before replacing the sensor. Replacement is usually simple, though some sensors sit behind other parts. Some vehicles need a crankshaft position relearn afterward.
What makes these sensors fail
- Heat cycling, which is why hot stalling is a classic symptom
- Oil leaks soaking the sensor or connector
- Chafed or broken wiring, and corroded connectors
- Damage to the reluctor wheel, or debris on a magnetic sensor tip
Can you drive with a bad crankshaft position sensor?
It is risky: a failing sensor can shut the engine off without warning in traffic. Have it diagnosed and replaced promptly.
LS swaps: 24x vs 58x
GM’s Gen III LS engines use a 24-tooth (24x) crank reluctor and Gen IV engines a 58-tooth (58x) reluctor, and the engine computer must match the engine’s signal. That detail matters when pairing an engine with a computer and harness in a swap; see the LS swap guide and LS engine specs.
More guides: camshaft position sensor · car won’t start · engine stalling · what does a crankshaft do?.
Trouble codes: P0335 Crankshaft Position Sensor · P0336 Crank Sensor Range/Performance · P0340 Camshaft Position Sensor · P0341 Cam Sensor Range/Performance · P0345 Cam Sensor A Bank 2 · P0365 Cam Sensor B Bank 1 · P0016 Crank/Cam Correlation Bank 1 A · P0339 Crank Sensor Intermittent · P0219 Engine Overspeed · P0320 Engine Speed Input Circuit · P0322 Engine Speed Input No Signal · all OBD2 codes.
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