An engine that cranks normally but never fires is missing one of the three things every cylinder needs: spark, fuel, or compression. The starter is clearly fine — it's turning the engine — so this branch is about which of the three is absent. This guide (part of the car-won't-start series) tests them in the fastest order. If the engine doesn't turn over at all, use the no-crank guide instead.
Start with the two fast checks
Fuel-pump prime. Turn the key to "on" (not start) and listen near the fuel tank for a two-second buzz. No buzz points at the pump, its relay, or fuse. Note: many keyless / push-to-start vehicles prime the pump when you open the door or unlock the car, not at key-on — so have a helper listen the moment you unlock it before you condemn a working pump.
Spark test. Pull a coil or plug wire, fit a known-good plug or spark tester, ground it, and crank. No spark points at ignition or the crank sensor.
Those two checks tell you which of the branches below to chase.
No spark
The most common no-spark, no-start cause is a failed crankshaft position sensor — without its signal the PCM won't fire the coils or injectors at all. Also suspect the ignition coil or module, the ignition switch, or an immobilizer blocking the start (flashing security light). Test the crank and cam sensors and the ignition coil. A relevant stored code such as P0335 (crank sensor circuit) points straight here.
No fuel
If there was no prime buzz, check the fuel-pump fuse and relay first — they're cheap and fail often — then the pump itself. Confirm with a fuel-pressure gauge; a pump that hums but makes no pressure is dead. A clogged filter or a failed pressure regulator can also starve a cranking engine. Our fuel-pressure and pump guide covers the tests.
No compression (timing)
If you have spark and fuel but still no start, and especially if the engine cranks unusually fast and smooth, the timing belt or chain may have snapped or jumped — the camshaft is no longer turning with the crankshaft. On many engines this also bends valves. A quick compression test confirms it: little or no compression across all cylinders means a timing failure, not an ignition or fuel problem.
Repair cost (2026 US ranges)
US independent shop at about $110–$160/hour plus parts. Planning figures, not a quote.
Repair
Shop (parts + labor)
DIY parts
Crankshaft position sensor
$150–$400
$30–$180
Fuel-pump relay / fuse
$60–$200
$10–$60
Fuel pump
$600–$1,200
$150–$450
Ignition coil / module
$150–$500
$40–$300
Immobilizer / key reprogram
$150–$500
—
Timing belt (often with water pump)
$500–$1,200
$60–$300
Timing chain
$1,000–$3,000
$150–$600
Diagnosis
$100–$200
—
FAQ
What is the most common reason a car cranks but won't start?
A dead fuel pump and a failed crankshaft position sensor are the two most common causes. Check for a fuel-pump prime and test for spark to split fuel from ignition quickly.
Can a bad crankshaft sensor stop the engine from starting?
Yes. On most engines the PCM needs the crankshaft position signal to fire spark and fuel, so a failed sensor causes a complete no-start with normal cranking, often with code P0335.
Will a broken timing belt let the engine still crank?
Yes — the starter still spins the crankshaft, but the camshaft no longer turns, so there's no compression or valve timing and it won't start. On interference engines a snapped belt often bends valves too.
General diagnostic information for US-market vehicles, not a substitute for a hands-on inspection. Costs are 2026 ballpark ranges for planning only.