Audi A4 Heat & HVAC Failure: Temp Sensor Warning Signs

Last month had nearly identical symptoms with my Audi A6 2009 2.0 TFSI. The vehicle maintenance report showed cooling system malfunction codes, and the temperature gauge readings were inconsistent. After thorough diagnostics, the issue was more complex than just a faulty temperature sensor. The entire heat exchanger had developed microcracks, causing a gradual coolant leak. This affected both engine cooling and the HVAC performance. The repair required: Replacing the heat exchanger unit, Installing new temperature sensors, Full cooling system flush, Refilling with fresh coolant, Recalibrating the climate control module Total repair time was 2 full working days. This was definitely a serious issue that needed immediate attention, as continued operation could have led to engine overheating and potential damage to the cooling system components. For proper diagnosis, the mechanic had to pressure test the entire system to locate the leak points. These symptoms often get misdiagnosed as simple sensor failures, but its worth having the complete cooling system checked when multiple HVAC issues occur simultaneously.

Thanks for sharing your experience with the A6. Dealing with the same issue on my A4 right now. The symptoms match exactly what you described. Just wondering, do you remember the total cost for all that work? Also, has everything been running smoothly since the repair? Really helps to know what to expect, especially with the cooling system issues these models seem prone to.

Just got back from having all this fixed on my A6, good to share the outcome. The sensor calibration and overall repair worked perfectly. Turns out the mechanic was right about the temperature sensor at the heat exchanger being defective, which they fixed. But the bigger cost came from the air conditioning control unit being defective too, that ran to 980 Euro for parts and labor. The engine cooling system is now working flawlessly, and the temperature gauge readings are steady and accurate. Its been about 3 weeks since the repair, and everything is running perfectly. The HVAC system responds immediately, and the engine maintains proper operating temperature. This kind of comprehensive fix was definitely worth it to prevent more serious issues down the line with the cooling system. The vehicle maintenance schedule is now back on track, and I havent seen any warning lights since. Definitely recommend getting it properly diagnosed and fixed rather than trying temporary solutions.

Finally got everything sorted with my A4. After reading about your experience, I took it to a different mechanic who specializes in European cars. Smart move, they found the exact same issue with microcracks in the heat exchanger. The repair took 3 days total. They replaced the heat exchanger, installed new temperature sensors, and did a complete flush of the cooling system. The sensor calibration was spot on, no more false readings on the temperature gauge. Total cost came to 1150 Euro, which included parts and labor. More than I initially expected, but the HVAC system works perfectly now and the engine cooling is back to normal. No warning lights or error codes since the fix. Definitely glad I asked here first, saved me from a potential misdiagnosis and possibly more expensive repairs down the line. The cooling system issues these models have are tricky, but at least now I know what to watch for in the future.