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.
Section 490 (Defogger System): Inspection
- CHECK DEFOGGER SWITCH CIRCUIT
Disconnect the connector from the heater control assembly, and check the connector on the wire harness side.
DEFOGGER SWITCH CIRCUIT SPECIFIED CONDITIONSTester Connection Condition Specified Condition 1 - Body ground Ignition switch OFF --> ON Below 1 V --> 10 - 14 V 4 - Body ground Light control switch OFF --> TAIL Below 1 V --> 10 - 14 V 6 - Body ground Constant Continuity 7 - Body ground Ignition switch OFF --> ON Below 1 V --> 10 - 14 V 9 - Body ground Constant Continuity If the circuit is as specified, replace the heater control assembly.
- INSPECT REAR DEFOGGER RELAY CONTINUITY REAR DEFOGGER RELAY CONTINUITY
Tester Connection Specified Condition 3 - 5 No continuity 3 - 5 Continuity (When battery voltage is applied to terminals 1 and 2) If the continuity is not as specified, replace the relay.
- w/ Mirror heater: INSPECT MIRROR HEATER OPERATION
- Connect the positive (+) lead from the battery to terminal 2 and the negative (-) lead to terminal 6.
- Check if the mirror becomes warm.
HINT:
It will take a short time for the mirror to become warm. If the mirror does not become warm, replace the mirror assembly.
- INSPECT DEFOGGER WIRE NOTE:
- When cleaning the glass, use a soft, dry cloth and wipe the glass in the direction of the wire. Take care not to damage the wires.
- Do not use detergents or glass cleaners with abrasive ingredients.
- When measuring voltage, wind a piece of tin foil around the top of the negative probe and press the foil against the wire with your finger.
- Turn the ignition switch ON.
- Push the defogger switch ON.
- Inspect the voltage at the center of each heat wire.VOLTAGE & CRITERIA
Voltage Criteria Approx. 5 V Okay (No break in wire) Approx. 10 V or 0 V Broken wire HINT:
If there is approximately 10 V, the wire is broken between the center of the wire and the positive (+) end. If there is no voltage, the wire is broken between the center of the wire and ground.
- Place the voltmeter positive (+) lead against the defogger positive (+) terminal.
- Place the voltmeter negative (-) lead with the foil strip against the heat wire at the positive (+) terminal end and slide it toward the negative (-) terminal end.
- The point where the voltmeter deflects from zero to several V is the place where the heat wire is broken.
HINT:
If the heat wire is not broken, the voltmeter indicates 0 V at the positive (+) end of the heat wire but gradually increases to about 12 V as the meter probe is moved to the other end.
- IF NECESSARY, REPAIR DEFOGGER WIRE
- Clean the broken wire tips with grease, wax and silicone remover.
- Place the masking tape along both sides of the wire to be repaired.
- Thoroughly mix the repair agent (Dupont paste No. 4817 or equivalent).
- Using a fine top brush, apply a small amount to the wire.
- After a few minutes, remove the masking tape.
- Do not use the defogger wire for at least 24 hours.
NO RELATED
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
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.