Audi RS4 Defrosters Failed After Routine Service

Had a similar situation with my 2004 Audi S4. The rear defroster and front heating system failed simultaneously after what should have been routine maintenance. The root cause was actually a failing battery combined with a voltage regulator issue. When the battery voltage drops too low, the car safety system disables high-draw components like the defroster to protect the electrical system. This triggers error codes related to the thermal window systems. In my case, the mechanic had accidentally left some equipment connected during service which drained the battery. This caused a cascade of electrical issues affecting both the rear window defroster and front heating components. The fix required: 1. Battery load testing and replacement 2. Voltage regulator inspection 3. Reset of the electrical system 4. Testing all defroster grid lines 5. Full system diagnostic scan This was a serious electrical system issue that needed immediate attention to prevent damage to other components. Your symptoms match this scenario precisely. Would recommend having the battery and charging system tested before assuming the heating system itself is faulty. The original mechanic should diagnose this under warranty if the problems started right after service. Worth getting their assessment first before seeking a second opinion.

Thanks for sharing your experience. My defroster repair was completed last month and everything works perfectly now. The rear defroster and front heating system are back to normal. The window demister functions are all responding correctly too. Did you remember how much the electrical system fix cost you? My repair bill seemed high at 780 Euro for all the testing and parts. Also wondering if youve had any other heating issues pop up since getting it sorted?

Had my auto defrost system repaired back then and no heating issues since. The thermal window system has been working flawlessly after they fixed the battery problem. Much simpler fix than expected, just needed a new battery since the old one was heavily discharged and failing. My total bill came to 290 Euro, including diagnostic testing and the replacement battery. Much less than your repair cost, but prices can vary based on what exactly needed fixing. The key was catching the battery issue before it could damage other electrical components. Really glad to hear your rear defroster and front heating are working properly now. Proper car defrost function is essential, especially during cold weather. Having both systems fail at once can be quite concerning, but often the root cause is simpler than it seems.

I went back to the original shop last week and glad I did. Turned out the window heater problems were caused by a damaged wire harness that got pinched during the routine service. The mechanic owned up to the mistake right away. The shop fixed both the front and rear defroster systems under warranty since it was their error. They replaced the damaged wiring, ran a full system diagnostic, and checked the car defrost functions multiple times to ensure everything worked properly. Very professional about correcting their mistake. Total repair time was about 4 hours. Would have cost around 780 Euro if I had to pay, but they covered it completely. All the window demister functions are working perfectly now, both front and rear. No error codes since the fix. Really appreciate the advice about going back to them first. Saved me from spending money elsewhere when they were willing to make it right. The heating system is back to normal and I actually trust this shop more now after seeing how they handled their mistake.