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.
1990 Jeep WagoneerFACTORY OEM SERVICE PROCEDURE
Power Circuits (2.5L)
- Using a voltmeter, check for battery voltage between ECU terminal No. 4 and ground. See Fig 1 and Fig 2 . If battery voltage is not present, check for an open in Red wire between ECU and battery.
- Turn ignition switch to the ON position. Using a voltmeter, check for battery voltage between ECU terminal No. 3 and ground. See Fig 1 and Fig 2 . If battery voltage is not present, check for an open in Black wire between ignition switch and terminal No. 3 of ECU, or check for a defective ignition switch.
- Connect a voltmeter between ground and ECU terminal No. 29. See Fig 1 and Fig 2 . Turn ignition switch to the START position. Battery voltage should be present between control unit terminal No. 29 and ground ONLY when ignition switch is in the START position. If voltage is not present, check for an open in Green wire between ECU terminal No. 29 and start relay, or check for a defective ignition switch.
Factory Service Tools
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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.