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.
1986 Mazda 626 BaseFACTORY OEM SERVICE PROCEDURE
Code 5 (Feedback System)
- Start and run engine at 2500 RPM for one minute. See if tester still displays Code 5. If so, check whether or not Green light (on tester) comes on at idle.
- If Green light does not come on, check for air leaks in intake air system and for insufficient fuel injection. If Green light comes on, clean or replace spark plugs. After service, measure oxygen sensor voltage.
- If voltage is incorrect, replace oxygen sensor. If voltage is correct, measure voltage at terminal "2D" of ECU. If reading is correct, replace faulty ECU. If reading is incorrect, check for open or short circuit in wiring harness from oxygen sensor to terminal "2D" of ECU connector.
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.
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