Unscheduled shut-down

Check for spark when it doesn't start. If it's missing, suspect the camshaft position sensor or crankshaft position sensor. Normally when they fail, it will be detected by the Engine Computer which will turn on the Check Engine light and set a diagnostic fault code in memory. When these sensors fail, often when they get warm, the lack of pulses from them tells the Engine Computer that the engine has stopped running, as in a crash that ruptures a fuel line, so the computer turns off the automatic shutdown (ASD) relay. That removes power to the ignition coils, injectors, alternator field, and fuel pump or pump relay. Also, when one of these sensors fails, you will still hear the fuel pump run for one second after turning on the ignition switch.

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