SQ5 Transmission Failure Linked to Oil Cooler Issues

Having some experience with transmission cooling issues, I dealt with similar symptoms on my 2011 S4 last year. The transmission also went into limp mode and showed warning lights. A proper leak detection test revealed the issue was actually due to a faulty wiring connection at the transmission oil pressure sensor. The main problem was that the connector had corroded over time, causing incorrect pressure readings which made the transmission computer think there were serious issues. This triggered the safety mode and rough shifting. The radiator coolant and cooling system were actually fine in my case. The repair involved cleaning the connector and replacing the damaged wiring and plug. Total cost was 95 Euro for parts and labor. After the fix, the transmission went back to shifting smoothly with no warning lights. To better understand your specific situation, could you share: Current mileage on your SQ5, Any transmission service history, Whether the grinding noise happens in specific gears, If the car overheating light has ever come on, Whether the cooling fan operation seems normal This information would help determine if your issue is similar to what I experienced or if its something else with the transmission cooling system.

Thanks for checking. My SQ5 just had its service 2 weeks ago at 44201 KM. After the cooling fan started making unusual noises, I took it back to have the radiator coolant system inspected. The mechanic found signs of transmission fluid mixing with engine coolant in the oil cooler assembly, suggesting internal damage. I checked my service records and noted the oil cooler was never replaced since new. The grinding occurs mainly during 2-3 and 4-5 gear changes. The leak detection test showed the transmission temperature running higher than normal, though no overheating warning has appeared yet. Let me know if your repair path involved checking these components specifically. I am trying to avoid a complete transmission replacement if the root cause is in the cooling system.

The symptoms you describe are definitely different from what I encountered with my S4. The mixing of transmission fluid with coolant that your mechanic found points to a failed oil cooler, which is more serious than the electrical issue I had. A pressure gauge test on my car showed normal readings once the wiring was fixed, while your situation involves actual fluid contamination. When transmission fluid mixes with coolant, it often leads to exactly the symptoms you mention, rough shifting, grinding, and limp mode activation. The transmission is likely shifting poorly and making noise because its not getting proper cooling, plus the contaminated fluid isnt providing proper lubrication. The car overheating issues and cooling fan noise make sense given this diagnosis. The compromised oil cooler is preventing proper heat exchange between the transmission and cooling system. In my research after my own repair, I learned that oil cooler failure is actually a known weak point on these models. The repair typically costs between 800-1200 Euro depending on parts availability. While not cheap, its far less expensive than transmission replacement. Given the similar platform between our cars and the clear evidence of cross-contamination, I strongly recommend replacing the oil cooler and doing a complete fluid flush of both systems. This should resolve the coolant leak and restore proper transmission operation before permanent damage occurs.

Current mileage is 44201 KM and service history is up to date. Thanks for explaining your situation, it sounds similar but my case appears more severe. After getting the radiator coolant system checked, they confirmed transmission fluid contamination in the oil cooler, which explains the grinding during gear changes and fan issues. A leak detection test showed elevated transmission temperatures, though no overheating warnings yet. The pressure gauge readings were concerning enough that my mechanic wants to address this before it leads to complete transmission failure. This seems quite different from your electrical connector issue. The mixing of fluids through a failed oil cooler makes more sense given my symptoms. I will proceed with the oil cooler replacement and system flush as suggested, since 800-1200 Euro is much better than a full transmission replacement. Will update once the repair is completed in case others encounter similar problems with failing oil coolers causing transmission issues.