SQ7 Overheating Linked to Faulty Bypass Valve & Coolant

Had a similar situation with my S5 2017 gasoline model. The symptoms started with running hot and error codes, which turned out to be more complex than initially diagnosed. The coolant leak warning was actually a secondary issue caused by pressure problems in the vacuum system. The primary cause was a failing bypass valve that was putting extra stress on multiple components, leading to a chain reaction affecting the entire exhaust system and engine cooling. The initial mechanic missed these connections, but the root cause became clear when the power loss started affecting performance. The proper fix required: Complete bypass valve replacement, Vacuum system integrity check, Coolant system pressure test, Air intake inspection, Full diagnostic scan This was a serious repair job requiring specialized diagnostic equipment. The bypass valve failure, if left unchecked, could have caused major engine damage. The complete diagnosis and repair took 3 days, as they needed to verify all connected systems were functioning properly after the fix. Would strongly suggest finding a specialized shop with experience in modern turbocharged engines, as these issues require specific expertise to properly diagnose the interconnected systems.

That was exactly my problem too. The engine stalling started soon after those first symptoms showed up, making the car practically undriveable. Thanks for sharing your experience. Looking back at the repair path you described, it matches perfectly with what I encountered. The vacuum system issues and the coolant leak warnings were definitely connected. The air intake problems developed gradually, making the initial diagnosis tricky. Did you remember the total cost for the complete fix? And has everything been running smoothly since the repair? Just want to make sure I am prepared for what might come up, as I am planning to take it to a specialized shop next week.

Since having the bypass valve malfunction properly diagnosed and fixed, my S5 has been running perfectly with no engine stalling or overheating issues. The specialized shop identified the root cause immediately, explaining how the vacuum system problems were triggering the secondary issues. The repair itself was fully covered under warranty since it was proven to be a consequential error from a previous repair, costing 0 Euro for the complete fix. This included the thorough testing of all connected systems, from the air intake to the cooling components. The difference in performance after the repair was remarkable. No more warning lights, perfect engine temperature, and the car runs as smoothly as it should. Going to a specialized shop made all the difference in getting an accurate diagnosis and proper repair the first time around. Just make sure your chosen shop has experience with modern turbocharged engines, as the interconnected nature of these systems requires specific diagnostic expertise.

Thanks everyone for the detailed responses. After taking it to a specialized performance shop last week, I can now share how my situation was resolved. The new mechanic found the exact cascade of issues, failing bypass valve leading to vacuum system problems and eventual coolant issues. The complete repair included replacing the bypass valve, fixing a cracked vacuum line, and a full system diagnostic check to ensure no engine overheating would occur again. Total cost came to 1200 Euro, including parts and labor. While not cheap, it was worth every cent as the car now runs perfectly. No more error codes, normal operating temperature, and the engine performance is back to where it should be. The fuel efficiency has also improved significantly since the repair, which was an unexpected bonus. Really glad I switched to a shop specializing in these engines, their diagnostic approach and expertise made all the difference in getting it fixed right the first time.