What causes car cranks but won't start?

Failed crankshaft (or camshaft) position sensor; Fuel delivery failure; No spark / ignition fault; Security / immobilizer or key issue; Clogged fuel injectors or bad fuel; Timing belt or chain failure.

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Car Cranks But Won't Start: Why and What to Do

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If the engine turns over (cranks) when you turn the key but never catches and runs, the starter and battery are fine, the problem is that the engine is missing one of the three things it needs: fuel, spark, or proper timing. Common culprits include a failed crankshaft position sensor, a fuel delivery problem, or an ignition fault. Some causes are simple, but a few can leave you stranded, so it's worth diagnosing carefully.

Trouble codes you may see

If you scan the car, these are the OBD-II codes most often behind this symptom:

P0335 P0336 P0340 P0341 P0230 P0231 P0087P0090P0011

Common causes

1
Failed crankshaft (or camshaft) position sensor
The computer uses the crank sensor to time fuel injection and spark; without its signal, you get no spark and no fuel and the engine cranks but won't start. Commonly sets P0335 or P0340 and is a frequent cause of sudden no-starts.
2
Fuel delivery failure
A dead fuel pump, blown fuel pump fuse or relay, or a clogged filter means no fuel reaches the cylinders. You often won't hear the pump prime for a couple seconds when you turn the key to ON.
3
No spark / ignition fault
Failed ignition coils, a faulty crank/cam sensor, or an ignition module problem can cut spark entirely, so the engine cranks without firing.
4
Security / immobilizer or key issue
A failed key transponder or anti-theft fault can disable fuel and spark even though the engine cranks normally. A flashing security light on the dash is the tell.
5
Clogged fuel injectors or bad fuel
Severely clogged injectors, or contaminated/old fuel (or water in the tank), can prevent combustion despite normal cranking.
6
Timing belt or chain failure
A snapped timing belt or jumped timing means the valves and pistons are out of sync, so the engine cranks freely but can't run, and on interference engines this can mean internal damage.

What to do

You're likely going nowhere until it's fixed, but you're not in immediate danger. Listen for the fuel pump priming when you turn the key to ON, check for a flashing security light, and scan for codes, P0335/P0340 points to a sensor. If the pump is silent or you suspect timing, or if you can't pinpoint it, have it towed to a shop rather than cranking repeatedly.

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Common causes

Failed crankshaft (or camshaft) position sensor

The computer uses the crank sensor to time fuel injection and spark; without its signal, you get no spark and no fuel and the engine cranks but won't start. Commonly sets P0335 or P0340 and is a frequent cause of sudden no-starts.

Fuel delivery failure

A dead fuel pump, blown fuel pump fuse or relay, or a clogged filter means no fuel reaches the cylinders. You often won't hear the pump prime for a couple seconds when you turn the key to ON.

No spark / ignition fault

Failed ignition coils, a faulty crank/cam sensor, or an ignition module problem can cut spark entirely, so the engine cranks without firing.

Security / immobilizer or key issue

A failed key transponder or anti-theft fault can disable fuel and spark even though the engine cranks normally. A flashing security light on the dash is the tell.

Clogged fuel injectors or bad fuel

Severely clogged injectors, or contaminated/old fuel (or water in the tank), can prevent combustion despite normal cranking.

Timing belt or chain failure

A snapped timing belt or jumped timing means the valves and pistons are out of sync, so the engine cranks freely but can't run, and on interference engines this can mean internal damage.

What to do