The Engine Computer turns on the automatic shutdown, (ASD) relay for one second when the ignition switch is turned on, then again during engine rotation, (cranking or running). That relay sends current to the ignition coil(s), injectors, alternator field, oxygen sensor heaters, and fuel pump or pump relay. The computer knows the engine is rotating by the signal pulses it receives from the crankshaft position sensor and the camshaft position sensor.
If a fuel line is ruptured in a crash, there will be no fuel pressure, and the engine will stall. Once stalled, there will be no signal pulses, so the computer will turn the ASD relay off. That stops the fuel pump from dumping raw fuel onto the ground where it would create a fire hazard.
If the engine runs, the ASD circuit is working, and there's nothing to check there.
Tuesday, February 21st, 2017 AT 4:27 PM