Audi S5 Transmission Failure Linked to Oil Cooler Issues

As someone with some hands-on experience working on Audis, I had a similar issue with my 2012 Audi S4 last year. The symptoms you describe match what I encountered, particularly the transmission slipping and warning lights. In my case, the root cause was a faulty wiring connection to the transmission oil pressure sensor, which ties into the cooling system. The sensor wasnt properly communicating with the transmission control unit, causing the car to enter limp mode as a safety measure. A pressure gauge test revealed normal readings in the cooling system, but the electrical signals weren't being transmitted correctly. After leak detection tests ruled out any coolant or oil leaks, the workshop found the damaged wiring connection to the sensor. The radiator coolant circulation was actually fine, but the system was getting false readings. The repair involved replacing the wiring harness and connector to the sensor, which solved all the symptoms. Total cost was 95 Euro for parts and labor. Before suggesting specific solutions though, could you provide: Current mileage on your S5, When was the last transmission service done, Any previous transmission-related repairs, Whether the cooling fan operates normally, If the transmission fluid level has been checked recently This information would help determine if your issue is similar to what I experienced or if its potentially something else.

Thanks for the detailed reply. The cooling fan operates normally according to the mechanic who checked it last week during my regular service at 49029 KM. No previous transmission repairs were needed before this issue. The pressure sensor readings are concerning, but the transmission fluid level is within normal range. The workshop quoted around 450 Euro for diagnostic tests to pinpoint if the oil cooler is the root cause. Just wanted to confirm if this pricing seems reasonable before proceeding.

Your situation sounds very similar to what I went through, though my repair was less extensive. Since your mileage is relatively low at 49K, and you mention the transmission fluid level is good, Im more convinced its likely a sensor or wiring issue like I had rather than a major mechanical problem. The 450 Euro diagnostic fee seems a bit steep compared to my experience. My workshop did complete pressure testing of the cooling system and electrical diagnostics for about 200 Euro. However, if they are planning to inspect the oil cooler connection to the radiator and do a full transmission pressure test, the higher cost might be justified. One thing I learned from my repair is that transmission problems that appear suddenly, like in your case, often point to electrical or sensor issues rather than mechanical wear. Before authorizing the full diagnostic, you might want to ask if they can first check the wiring connections to the pressure sensor in the cooling system, since this is a known weak point in these models. After my repair, I also had them perform a transmission fluid flush as preventive maintenance, which helped ensure smoother shifting. The total system holds about 9 liters of fluid, so factor that into potential repair costs if they recommend a fluid change. My suggestion would be to start with the simpler electrical checks before moving to more complex diagnostics of the radiator repair components.

Thanks for mentioning your diagnostic fee experience. Given the initial symptoms point to the oil cooler in the cooling system, I will proceed with the workshop's diagnostic testing. Better to identify any potential car overheating issues or coolant leaks now before they cause more damage. After getting your input, I called another workshop for a second opinion, and they quoted 400 Euro for similar diagnostic tests, so the 450 Euro seems to be the going rate. They also mentioned they would do a full leak detection test to check both the transmission and cooling system components. I will ask them to specifically inspect the wiring connections first as you suggested. Makes sense to rule out simpler electrical issues before diving into more complex radiator repairs. I will update once I get the results back from the diagnostic tests. The transmission fluid level being normal is at least one positive sign.