Audi Q3 Coolant Mystery: Overheating Despite Full Level

Had nearly identical issues with my 2012 Audi Q5 2.0 TFSI. Based on some experience working on these engines, this sounds like a common fault pattern. The symptoms you describe matched mine perfectly, overheating, check engine light, and coolant leaks. After initial confusion from different workshop opinions, the real problem turned out to be a wiring issue affecting the coolant temperature sensor signals. The diagnostic trouble codes showed erratic temperature readings. A detailed inspection revealed a damaged data link connector between the engine control module and temperature sensors. The CAN bus signals were getting corrupted, causing the cooling fan to operate incorrectly. The fix involved replacing the wiring harness section and reprogramming the control module, cost me 95 Euro for parts and labor. Since then, zero issues with temperature control or coolant leaks. To help diagnose your specific case more accurately, could you share: What diagnostic trouble codes are showing? Does the temperature gauge show erratic readings? When exactly does the cooling fan activate? Have you noticed any electrical issues in other systems? This way we can determine if your Q3 is showing the same electrical symptoms mine had.

Thanks for the insights. Just had my latest service at 30039KM, and they found no cooling system issues during inspection. Since my post, Ive noticed the temperature gauge fluctuates wildly, especially at idle. The fan seems to activate out of nowhere regardless of engine temperature. Got the diagnostic codes scanned: P0117 and P0118, pointing to a communication fault in the temperature sensor circuit. Interesting that your Q5 had similar connectivity issues. Starting to think the CAN bus signals might indeed be the root cause rather than a mechanical cooling system problem. When did your control unit start working normally after the repair? My system occasionally shows normal readings for a few minutes before acting up again.

Thanks for the follow-up details. Those diagnostic codes P0117/P0118 are exactly what my Q5 showed before the repair, confirming our issues are likely identical. The erratic temperature gauge behavior and unusual fan activation perfectly match the CAN bus communication problems I experienced. After the control module repair and wiring harness replacement, my system stabilized immediately. The temporary normal readings you mentioned are typical of intermittent data link failures, the control unit receives correct signals briefly before losing proper communication again. The fact your recent service found no mechanical cooling issues further supports this being an electrical problem. In my case, the software glitch appeared gradually, but once the control unit started misreading the temperature data, the symptoms quickly worsened. Our shared symptoms really point to the same root cause: Fluctuating temp readings, Unusual fan operation, Clean mechanical inspection, Matching error codes, Intermittent normal operation The repair cost has likely stayed similar, around 95 Euro for the complete fix. Word of caution: delaying the repair might lead to unnecessary strain on cooling components due to improper fan control. Would recommend getting the data link connections checked first, as this is often overlooked in favor of replacing mechanical parts.

Since everyone here seems to agree on the electrical nature of the problem, I went ahead and scheduled a diagnostic session focusing specifically on the wiring and control module. The shop confirmed they will first check the data link connections and CAN bus signals before looking at any mechanical components. Really helpful to hear about the identical diagnostic trouble codes and similar symptoms. Gives me confidence we are on the right track, especially since my recent service showed no mechanical issues. The fact that both vehicles show the same pattern of connectivity issues with the temperature sensors is quite telling. Will update once they complete the inspection. The quoted price range matches what was mentioned, roughly 100 Euro for the potential wiring harness replacement and control module reprogramming. Just hoping the repair provides the same immediate resolution you experienced with your vehicle. The unusual fan activation and temperature fluctuations are getting worse, so looking forward to getting this resolved.