While the engine runs
Car stalls by itself: causes and what to do
An engine that stalls on its own, when coming to a stop, pressing the clutch or once warm, cannot hold its idle. It usually comes down to idle control, an air leak, the fuel supply or a sensor the control unit needs to keep it running, such as the crankshaft sensor.
See a garage soonWhile the engine runs
Reviewed by Daniel Morales, founder of Reprorace SL, on
Is it serious? Can I keep driving?
Carefully, and only as far as the garage. Have it checked soon: if the engine stops on the move, steering and brake assistance are lost and turning and braking take more effort. If it happens on the road, grip the wheel firmly, press the brake harder and pull over when it is safe.
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
- Idle control or throttle: dirt or a throttle motor fault that cannot hold the revs.
- Air leaks: an air leak leans out the mixture at idle.
- Fuel supply: a pump, filter or regulator losing pressure.
- Crankshaft or camshaft sensor: heat can cut its signal and the engine stops dead.
- Clutch or torque converter: on automatics, a converter that does not unlock can stall the engine when stopping.
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? What does the throttle body do and why does a fault trigger limp mode? What is a mass airflow sensor and what symptoms does it cause when it fails?
Car system: Fuel and air
What you can check yourself
Note when it stalls: cold, hot, when stopping, when turning the wheel or switching on the air conditioning.
Make sure there is enough fuel; the gauge can be wrong.
See whether it restarts at once or needs to cool down first: that points to a sensor.
Read the fault codes after the next stall, before clearing anything.
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
- P0505Idle control system: malfunction
- P0506Idle control system RPM: lower than expected
- P0335Crankshaft position sensor A, circuit: malfunction
- P0340Camshaft position sensor A (bank 1 or single sensor), circuit: malfunction
- P0087Fuel rail/system pressure: too low (bank 1)
- P0171Mixture too lean (bank 1)
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: idle speed, crankshaft speed signal, fuel pressure, coolant temperature and system voltage.
Frequently asked questions
Is it dangerous for the car to stall?
Yes, if it happens on the move or at a junction: you lose steering and brake assistance. Have it checked as soon as possible.
Why does it only stall when hot?
Many sensors, such as the crankshaft sensor, fail when hot and work again once cool. The fault code usually gives it away.
Could it be how I release the clutch?
If it only happens when pulling away, it may be technique. If it stalls when you stop or while driving, no: there is a fault.
Keep reading
- Fuel and air: how it works and what fails
- Rough idle: why the engine shakes or hunts when stationary
- Engine cranks but will not start: causes and what to do
- Car slow to start: 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