Audi A4 Overheating + Check Engine Light: Bypass Valve Fix

Had the same situation with my 2018 Audi A5 2.0T. The engine overheating and error codes were actually symptoms of a failing vacuum system, not just the bypass valve. The root cause was a cracked diverter valve that affected the entire air intake system. The vacuum leak caused irregular pressure in the system, leading to engine stalling and overheating issues. The problem got worse over time, affecting multiple components connected to the vacuum system. The exhaust system sensors were also giving false readings due to the pressure inconsistencies. This turned out to be a serious issue requiring immediate attention. Left unchecked, it could have caused significant engine damage. The repair involved replacing the diverter valve, checking all vacuum lines, and recalibrating the engine management system. Based on the symptoms described, recommend getting a complete diagnostic scan focusing on the vacuum system and cooling circuit. The bypass valve might be part of the problem, but its often connected to other underlying issues in these engines.

Thanks for sharing your experience with the vacuum system and overheating problems. Did those fixes solve the issues completely? My A4 is showing similar symptoms and engine stalling occurs more frequently now, plus the power loss is noticeable during acceleration. Would be helpful to know if you remember the total repair costs and if any other problems came up since the repair was done? Trying to budget for the worst case here while looking for a reliable mechanic.

After getting the vacuum system fixed, the engine overheating and stalling problems were completely resolved. The mechanic found that the bypass valve malfunction was actually a consequential error stemming from the vacuum system issues, which they fixed at no extra charge. The fuel efficiency and overall performance returned to normal, and the power loss during acceleration is no longer an issue. The exhaust system readings are now consistently normal, with no error codes appearing for over 6 months. Since the repair, the car has been running smoothly with no related problems. This type of issue typically needs addressing right away to prevent more serious engine damage, but once properly fixed, it tends to stay fixed. You mentioned looking for a reliable mechanic, its important to find one who specializes in VAG engines, as they know these common vacuum system problems well. They should perform a complete diagnostic scan before starting any repairs to identify all related issues.

Thanks for the detailed feedback. I took my A4 to a specialist mechanic yesterday who confirmed the vacuum system diagnosis. The air intake was indeed compromised, leading to the engine overheating issues. They found multiple vacuum leaks and a deteriorated bypass valve. The total repair came to 850 Euro, which included replacing the diverter valve, fixing vacuum leaks, and a thorough system check. While not cheap, the car already feels much better, no more engine stalling or power loss during acceleration. The exhaust system readings are now normal and the check engine light has stayed off. Definitely worth getting it fixed properly rather than trying cheaper temporary solutions. The mechanic also showed me all the damaged parts and explained the repairs, which was refreshing after my previous experiences.