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.
1988 Ford Bronco II 4WD, Standard, M5OD-R1FACTORY OEM SERVICE PROCEDURE
Test Procedure
- Deactivate SELF-TEST (disconnect jumper wire). Start engine and run it at 2000 RPM for 2 minutes to warm up HEGO sensor. Turn engine off and wait 10 seconds.
- Start engine. Insert jumper to activate SELF-TEST. The engine ID code will be displayed. On vehicles equipped with Brake On/Off switch (BOO) the brake pedal MUST be depressed and released AFTER the ID code (within 1-2 seconds). On vehicles equipped with Power Steering Pressure Switch, the steering wheel MUST be turned one-half turn and released AFTER the ID code.
- If a Dynamic Response code occurs, briefly depress accelerator pedal to wide open throttle (WOT). A Dynamic Response code is a code 1 or 10 displayed after the Engine ID code and before the Engine Running codes. DO NOT depress throttle during test unless a Dynamic Response code occurs. The ENGINE RUNNING SELF-TEST service codes will then be displayed. Observe and record all codes.
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.