Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSJEEP1991CHEROKEE 2WD L4-150 2.5L VIN P MFIREPAIR AND DIAGNOSISRELAYS AND MODULESRELAYS AND MODULES - POWERTRAIN MANAGEMENTRELAYS AND MODULES - COMPUTERS AND CONTROL SYSTEMSMAIN RELAY (COMPUTER/FUEL SYSTEM)DESCRIPTION AND OPERATION
1991 Jeep Cherokee 2WD L4-150 2.5L VIN P MFI
Main Relay (Computer/Fuel System): Description and Operation
1991 Jeep Cherokee 2WD L4-150 2.5L VIN P MFISECTION 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.
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.