Starting, battery and electrics
Engine cranks but will not start: causes and what to do
If the starter turns the engine normally when you turn the key or press the button but the engine never fires, something the combustion needs is missing. It is usually fuel, spark or preheating, the signal from a sensor such as the crankshaft sensor, or the immobilizer's permission.
Check without hurryStarting, battery and electrics
Reviewed by Daniel Morales, founder of Reprorace SL, on
Is it serious? Can I keep driving?
Usually not urgent, but do not ignore it. There is no risk while the car is parked somewhere safe. Do not keep cranking for long: you can flatten the battery and, on gasoline engines, flood the engine or damage the catalytic converter with unburnt fuel.
A careful, general answer: only someone who inspects the car can say whether it is safe to drive. When in doubt, stop somewhere safe and call for assistance.
Most likely causes
- Fuel: an empty tank even if the gauge shows some, a pump that does not work or a clogged filter.
- Immobilizer: the key is not recognized; a light with a key or a padlock usually flashes.
- Crankshaft or camshaft sensor: without its signal the control unit neither injects nor sparks.
- Preheating on a diesel: in the cold, failed glow plugs make starting very hard.
- Timing belt or chain: if it has broken, the engine turns more freely and sounds different; stop trying.
Listed from more to less common in general; on your car they may be different. A fault-code reading and a check at the garage confirm which one it is.
To understand it better: What do the crankshaft and camshaft sensors do and what happens when they fail? How can you tell if the 12 V battery is failing? What do U codes and lost communication (U0100) mean?
Car system: Engine and lubrication
What you can check yourself
Make sure there is fuel; if the gauge was low, add a few liters.
See whether the immobilizer light flashes and try the spare key.
When you switch the ignition on, listen for the fuel pump humming for a couple of seconds (on many cars you can hear it).
Make short attempts of a few seconds, resting the battery in between.
Safe checks only: with the engine off and cold whenever you look under the hood, without taking anything apart and without touching hot or moving parts.
Related fault codes
- P0335Crankshaft position sensor A, circuit: malfunction
- P0340Camshaft position sensor A (bank 1 or single sensor), circuit: malfunction
- P0016Correlation fault between crankshaft position and camshaft position (bank 1, sensor A)
- P0087Fuel rail/system pressure: too low (bank 1)
- P0627Fuel pump A, control circuit open
- P0190Fuel rail pressure sensor (bank 1), circuit: malfunction
Generic codes that often come with this symptom. Seeing one does not confirm the cause: it is where the diagnosis starts.
How the ECO-LITE helps diagnose it
Plugged into the OBD socket, the ECO-LITE reads the fault codes of the control units that answer, with the freeze-frame data captured when the fault happened, and shows live data on your phone or computer. With your permission, your garage can see them remotely before you bring the car in.
What to look at here: engine speed signal while cranking, fuel pressure, system voltage while cranking and coolant temperature.
Frequently asked questions
Why will it not start if the battery is fine?
Because the battery only turns the starter. Starting also needs fuel, spark or glow plugs, and the control unit receiving its signals.
How long can I keep trying to start it?
Attempts of a few seconds with pauses. Persisting flattens the battery and can overheat the starter.
Does the fault code help if it will not start?
Yes: codes can be read with the ignition on. P0335 (crankshaft), P0340 (camshaft) or P0087 (fuel pressure) are common clues.
Keep reading
- Engine and lubrication: how they work and what fails
- Car will not start and does nothing or just clicks
- Car slow to start: causes and what to do
- Car stalls by itself: causes and what to do
- Car symptoms: what they mean and what to do
- Check engine light on: what to do
- How to read and clear your car's fault codes
- OBD fault codes: what each one means