* Fuel System Problems: This could be anything from a faulty fuel pump (not delivering fuel), clogged fuel filter (restricting fuel flow), bad fuel injectors (not properly atomizing the fuel), or a problem with the fuel pressure regulator. A low fuel level is also a possibility, although that usually results in a sputtering or inability to accelerate before stalling.
* Ignition System Issues: A failing ignition coil, spark plugs, or distributor (in older cars) can prevent the engine from igniting the fuel-air mixture. A bad crankshaft position sensor (CKP sensor) or camshaft position sensor (CMP sensor) can also cause the engine to shut down as they tell the computer the engine's rotational position.
* Electrical Problems: A failing alternator (which charges the battery) will eventually drain the battery, leading to a stall. A short circuit or other electrical fault can also cause a sudden power loss. A faulty battery itself is another possibility.
* Computer Problems (Engine Control Module - ECM): The ECM is the "brain" of the car. A malfunctioning ECM can cause a variety of problems, including the engine unexpectedly shutting off.
* Transmission Problems: In automatic transmissions, issues can cause the engine to stall, though this is less common than other causes.
* Overheating: If the engine overheats severely, the car's safety systems might shut the engine off to prevent catastrophic damage.
* Vacuum Leaks: Significant vacuum leaks in the intake system can disrupt the engine's air-fuel mixture, causing it to stall.
In short: There's no single answer. The cause could be relatively simple (low fuel), or require extensive and expensive repairs. Do not attempt to diagnose or fix this yourself. Driving a car that shuts off unexpectedly is extremely dangerous. Get it towed to a qualified mechanic immediately.
