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 3 (Coolant Thermo Sensor)
- Check for poor connections at coolant thermo sensor connector. Repair or replace as necessary. If connections are okay, check resistance of coolant thermo sensor. If resistance is within 94-73,800 ohms, go to next step. If not, replace coolant thermo sensor.
- Measure voltage at terminal "2I" of ECU. If reading is 12 volts, check for open circuit in wiring harness. If reading is zero volts, check for short circuit in wiring harness from coolant thermo sensor to terminal "2I" of ECU connector. If short is not located, replace faulty ECU.
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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