Cherokee 2WD L4-150 2.5L VIN P MFI (1991)
Automatic Shut Down (ASD) Relay: Description and Operation
Power Distribution Center
The ASD relay supplies voltage to the ignition coil, and fuel injectors. It is not located inside the SBEC, but it is turned OFF and ON by the SBEC
(controls the ground). The Crankshaft Position Sensor (CPS) signal goes directly to the SBEC II, and in the event that the SBEC II sees no signal, the
ground is removed from the ASD circuit. If the ignition switch is ON and the engine is OFF, the SBEC II will allow the ground to be applied to the ASD
for approximately 3 seconds, then if no Crankshaft Position Sensor (CPS) signal is sensed the SBEC II removes the ground from the circuit. If the
ground is removed from the ASD relay circuit, then the ASD relay acts as an OPEN switch in the power circuits to the fuel injectors, and ignition coil
causing a no start condition.
