Audi S5 Heater Failure: Water Valve Mystery Solved

Having some experience with Audi models, I encountered a similar issue with my 2017 Audi S4, which shares many components with your S5. The symptoms matched exactly, poor heating performance and error codes related to the cooling system. After initial troubleshooting, my mechanic discovered a faulty cable connection at the water valve, which was causing intermittent valve blockage. This prevented proper coolant flow through the heater core, leading to the heating issues. The repair involved replacing the damaged wiring harness and checking the valve itself. Total cost was 95 Euro, which included diagnostic time and parts. Since the fix, the heating system has worked flawlessly with no coolant leak issues or engine overheating problems. To provide more specific guidance for your case, could you share: Current mileage on your S5, Exact error codes showing up, Whether you notice any coolant loss, If the issue is constant or only occurs sometimes, Temperature gauge behavior during normal driving These details would help determine if your problem matches what I experienced or if it might be something different in your heating system.

Thanks for investigating this. My 2019 S5 has 122619 KM and last service was completed 3 months ago. The error codes are P0597 and P2185. The issue seems pretty consistent now, happening every time I drive. I checked the coolant level and noticed it dropping slightly between refills. The temperature gauge stays normal during operation, but car heating remains minimal regardless of how long I drive. The mechanic initially thought it was just low coolant causing the heater core performance issues, but even after a proper refill and bleeding, the cabin still barely warms up. This makes me think the valve blockage theory could be right, especially given your similar experience with the wiring.

Thanks for providing those details. After seeing your error codes and symptoms, I am even more convinced your issue mirrors what I experienced with my S4. Those specific codes (P0597 and P2185) are exactly what my system showed before the repair. The coolant loss you mentioned is another important clue. In my case, the faulty wiring caused the water valve to stick partially closed, creating pressure buildup that led to minor coolant seepage. The engine coolant temperature stayed normal because enough flow remained for engine cooling, but the restricted flow through the heater core caused the poor cabin heating. Since your symptoms are developing the same way mine did, I would strongly recommend having your mechanic check the wiring connection at the water valve. The valve blockage can worsen over time, and waiting too long might lead to complete heating system failure. A few observations from my repair experience: The coolant loss stopped completely after fixing the wiring, Heating performance returned to normal immediately, No more error codes appeared after the repair, Engine cooling system maintained proper pressure The repair cost should be similar to what I paid (95 Euro), assuming the issue is indeed the same wiring problem affecting the water valve operation.

Thanks everyone for the detailed responses. After taking my S5 to the shop today, they confirmed the water valve wiring harness was indeed the culprit. The diagnostic showed intermittent signals to the valve, causing the flow restriction through the heater core that was affecting cabin heating. The repair cost was actually 85 Euro, slightly less than expected. They replaced the damaged wiring section and performed a complete coolant system bleed. The heating now works perfectly, cabin warms up quickly and maintains temperature consistently. No more error codes showing up on the dash either. For anyone else facing similar heating performance issues with error codes P0597 and P2185, definitely have your mechanic check the water valve wiring connections first. The symptoms of poor cabin heat combined with normal engine temperature and minor engine coolant loss seem to be clear indicators of this specific problem. Will monitor the coolant level over the next few weeks to ensure everything stays fixed, but so far the repair seems to have completely resolved both the heating and coolant leak issues.