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.
A/F Sensor Heater Relay: Inspection
- REMOVE RELAY BOX COVER
- REMOVE A/F SENSOR HEATER RELAY (Marking: A/F HTR)
- INSPECT A/F SENSOR HEATER RELAY CONTINUITY
- Using an ohmmeter, check that there is continuity between terminals 1 and 2.
If there is no continuity, replace the relay.
- Check that there is no continuity between terminals 3 and 5.
If there is continuity, replace the relay.
- Using an ohmmeter, check that there is continuity between terminals 1 and 2.
- INSPECT A/F SENSOR HEATER RELAY OPERATION
- Apply battery voltage across terminals 1 and 2.
- Using an ohmmeter, check that there is continuity between terminals 3 and 5.
If there is no continuity, replace the relay.
- REINSTALL A/F SENSOR HEATER RELAY
- REINSTALL RELAY BOX COVER
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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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