Symptoms
- Rear defroster button turns on but the glass never warms up or clears fog
- Rear window stays fogged or icy while the front defrosts fine
- Sometimes only part of the grid pattern is warm
- Button light comes on normally when pressed
Likely causes
- CommonBlown rear defroster fuseA simple, cheap first check that cuts power to the whole grid if blown.
- CommonBroken or scratched grid line on the glassThe thin heating lines on the inside of the glass can be scratched (often by an ice scraper) or corrode, breaking the circuit at that point.
- PossibleFaulty rear defroster relay or timerThe relay that supplies power for a set time when the button is pressed can fail even if the grid itself is fine.
- Less commonBad connection at the grid's power tabsThe small tabs where wiring connects to the glass can corrode or come loose.
What to do
- Check the fuse box for the rear defroster fuse and replace if blown.
- Inspect the inside of the rear glass closely for a visible scratch or gap in the thin horizontal grid lines, often from scraping ice with a hard tool.
- With the defroster on, carefully feel along the grid lines (glass should be warm, not hot) to find a spot where heat clearly stops, indicating a break.
- Use a defroster repair kit (conductive paint pen) to bridge a small break in a grid line if one is found.
- Check the relay by swapping with an identical one from another circuit if fuses and grid lines look fine.
- Avoid scraping the inside of rear glass with hard tools in the future; use a de-icer spray or run the defroster before scraping.
Tools and parts
- Multimeter
- Rear defroster repair kit (conductive paint)
Rear window defroster repair kitSearch: “rear defroster repair kit conductive paint”
When to call a pro
See a mechanic if the fuse and visible grid lines look fine but the defroster still doesn't work, since relay or wiring diagnosis may be needed.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.