An engine needs three things to keep running: fuel, air and a spark at the right moment, all controlled by the engine computer. A stall happens when one of them is interrupted. Finding which one is the key to the repair.
If your car stalls on the road
Turn on your hazard lights and steer to a safe place. Without the engine, power steering and brake assistance become much heavier, but they still work; push harder on the pedal and steering wheel. Try restarting once you are stopped safely. If it restarts, drive gently to a safe place or a garage; if it stalls repeatedly, call for help. Our guide to handling a breakdown covers safety at the roadside.
Fuel problems
- Running out of fuel, or a faulty fuel gauge.
- A failing fuel pump, which often causes stalling or loss of power under load or when hot.
- A clogged fuel filter or dirty injectors.
- Bad fuel, contaminated with water.
Air and sensor problems
The engine computer relies on sensors to mix fuel and air correctly. A faulty mass airflow sensor, a crankshaft or camshaft position sensor that cuts out when it gets hot, or a large vacuum leak can make the engine stall. A dirty or failing idle air control valve or electronic throttle body is a classic cause of stalling when you come to a stop.
Electrical and ignition problems
A failing alternator stops charging the battery, and the car runs until the battery is exhausted, often with dimming lights and a battery warning first. Worn spark plugs or a failing ignition coil cause misfires that may lead to stalling. Loose or corroded battery terminals can also cut power suddenly.
Manual gearboxes
In a manual car, the most common cause is simply releasing the clutch too fast or coming to a stop in gear without pressing the clutch. If stalling happens only in those situations, technique is the issue, not the car.
Finding the cause
If the check-engine light is on, read the trouble code; many parts stores do this for free. Note the circumstances: does it stall when hot, when cold, at idle, under acceleration, or when turning on the air conditioning? These details help a mechanic narrow it down. See what “service engine soon” means for more on warning lights, and how to find a good mechanic if you need help.
