Audi TT Defroster Failure: Front & Rear Fix Tips

I had a similar issue with my 1998 Audi A4 where both the front and rear window defroster stopped working simultaneously. Having some experience with electrical car issues, I first suspected it might be a simple fuse problem, but it turned out to be more complex. The workshop diagnosed a heavily discharged battery that was causing multiple electrical issues, including the window demister malfunction. The battery voltage was too low to properly power the heating elements in both the front and rear window defroster systems. The total repair cost was 290 Euro, which included: Battery testing and replacement, Electrical system diagnostic, Testing of both window heater circuits After the repair, both defroster systems worked perfectly again. The heating issue was completely resolved once the new battery was installed and properly charged. Before suggesting specific solutions for your TT, it would help to know: Have you noticed other electrical issues lately? Does the battery warning light come on? How old is your current battery? Are there any issues with starting the car, especially in cold weather? These details would help determine if your situation matches what I experienced with my A4.

Last service was done at 193515KM. Had the same defroster repair done, but my root cause was different. The thermal window heating failed due to broken connections at the rear window terminal points. The front defrost issue was related to a faulty relay. Total repair costs: Rear window heating terminal repair: 180 Euro, Defrost relay replacement: 95 Euro, System testing: 60 Euro The car defrost system now works perfectly. If your error codes point to circuit breaks, check the connection points first. My heating issue ended up being much simpler than expected, not a complete electrical system problem. Worth testing the relay before doing major work. A multimeter check of the rear window heating elements can help pinpoint exact failure points.

Thanks for sharing your repair experience. My A4 actually ended up having a similar terminal connection issue a few months after the battery replacement I mentioned. The rear defroster stopped working again, and inspection revealed corroded terminals at the heating coil connection points. Interesting that your heating issue involved both systems but had different root causes. The thermal window connections are definitely a common failure point on these models. My final repair costs were actually higher than yours: Terminal replacement and resoldering: 220 Euro, System diagnostics: 80 Euro, New heating coil harness: 150 Euro The car defrost system has been reliable since fixing both the battery and terminal issues. Running resistance tests on the rear window heating elements was key to finding the exact problem spots. Good call on checking the relay first, could save others unnecessary repairs. For tracking purposes, when did you first notice the thermal window systems failing? Mine started acting up around 180000KM, wondering if theres a common failure point.

Thanks for the shared experience about the relay issue. Yes, noticed the first signs of auto defrost problems around 175000KM, started with inconsistent rear defroster operation, then the front window heater began failing about a month later. Doing some follow-up maintenance next week. Having them check all heating coil connections while theyre working on it, since I noticed the drivers side window is taking longer to clear lately. Better to catch any developing issues early. Your repair costs actually match what other TT owners reported in the technical forums. The heating issue seems to follow a pattern, usually starts with connection problems, then spreads if not fixed promptly. Good you caught yours before needing a complete heating coil replacement. Just updated my service records: Full defrost system check: 335 Euro, New connections installed: 180 Euro, Testing all window heating circuits: 60 Euro Thermal window heating is critical for safe winter driving, so the investment was worth it. Will post an update after next weeks maintenance check.