When a car turns off by itself, it will stop moving.
A car may turn off by itself due to faulty electrical system, bad alternator, low fuel pressure, bad fuel pump, clogged fuel filter, clogged fuel lines, no fuel, low fuel, bad fuel or even due to bad sensors, internal engine problems etc.
A faulty crankshaft sensor, faulty MAF sensor or even bad battery could cause a car engine to turn off by itself.
When the engine loses power, the engine may shut down and the electrical system may shut down as well including the lights dimming or going off, radio not working and power steering, power brakes etc can get very hard to use.
The engine may start to run rough, the car might jerk, misfire etc and the car engine may make strange noises, or if the engine is overheating the temperature gauge will go up.
Some cars might shut the engine down when it gets to a too hot temperature when overheating to prevent damage.
If you notice the cars engine is about to stall, try to pull the car off to the side of the road as soon as possible.
Common causes of a car turning off by itself include issues with the fuel system, electrical ignition problems, bad sensors, bad air idle valves and controls, engine timing issues, low coolant, timing belt issues, bad timing belt, low oil pressure or in severe cases, bad head gasket or internal engine failure.
Low fuel, clogged fuel filters, bad fuel pumps, faulty fuel pressure regulator or dirty fuel injectors, or even bad fuel injectors can result in an engine shutting off by itself.
Malfunctioning crankshaft position sensors, camshaft sensor, MAF or Mass Airflow sensors that are bad or bad O2 sensors can also cause an engine to shut off by itself.
A dirty throttle body, stuck idle air control valve also known as an IAC valve, clogged or bad EGR valve and even vacuum leaks also can cause an engine to shut off by itself.
And issues with engine timing, bad spark plugs, overheating, bad water pump, low coolant, dirty coolant, timing belt issues, low oil pressure and internal engine pressure or low compression could result in an engine or car shutting off by itself.