RS6 Transmission Nightmare: Slipping Gears & Limp Mode

Let me share my experience with a similar transmission performance issue on my 2017 RS4. I have some experience working on cars, mainly basic maintenance and troubleshooting. The symptoms you describe match exactly what I encountered, erratic shifting, warning lights, and limp mode. After taking it to the workshop, they diagnosed an undervoltage issue affecting the transmission control unit, which was causing the automatic transmission to malfunction. The repair involved testing the electrical system and replacing some components. The total cost was 240 Euro, which included diagnostic work and parts. The car transmission returned to normal operation after the fix. However, before jumping to conclusions, it would be helpful to know: Have you checked the battery voltage? Are there any other warning lights active? When did you last change the hydraulic fluid? Does the issue occur more frequently when the engine is cold or warm? Regular maintenance like oil replacement and hydraulic fluid changes can prevent some transmission issues, but electrical problems require proper diagnosis. The workshop should check both the mechanical and electrical systems to ensure proper automatic transmission operation. Would you mind sharing these details? It would help narrow down whether your issue is similar to what I experienced.

Since the previous service at 95000 KM, transmission performance was flawless. Checking all points mentioned: battery is good at 12.6V, no other warning lights present. The slipping transmission occurs mainly when warm, about 15-20 minutes into driving. Last transmission flush and hydraulic fluid change was done during the regular maintenance schedule at 80000 KM. The automatic gearbox issues started suddenly last week with no prior warning signs. Oil replacement was done recently as part of routine maintenance. Based on the voltage reading, I doubt its an electrical issue, leaning more toward a mechanical problem.

Thanks for those details, interesting that we have such similar issues. After my electrical fix, I actually encountered another problem that sounds more like what you're describing. When my automatic transmission started acting up again with slipping transmission symptoms during warm operation, it turned out the transmission pressure sensor was failing. The symptoms matched yours perfectly, normal cold operation but problematic shifting once warm. The pressure sensor issue caused the transmission control unit to receive incorrect readings, leading to poor transmission performance and eventually forcing the automatic gearbox into limp mode. The sensor cost 180 Euro plus labor around 220 Euro for complete diagnosis and replacement. Since your maintenance schedule is similar to mine and the oil replacement is recent, I would suggest having the transmission pressure sensor checked first. The fact that the issues occur when warm strongly points to this, especially with good battery voltage. Quick tip: while waiting for the repair, try driving in manual mode if possible. This helped reduce stress on my transmission until I could get it fixed. Just avoid aggressive shifting and keep the RPMs moderate. Is the transmission fluid level showing correct on the dipstick? This would help confirm whether we're dealing with the same issue.

The pressure sensor theory makes a lot of sense, my symptoms align perfectly with what you described. Just checked the hydraulic fluid level on the dipstick and its showing normal. Since posting, I noticed the automatic gearbox performs slightly better in manual mode as you suggested. Looking at the repair costs you mentioned, 400 Euro total seems reasonable compared to a full transmission flush or major automatic transmission repair. Will get the pressure sensor checked first thing at the workshop. The fact that the issues mainly occur during warm operation really points toward this being the culprit. This has been incredibly helpful in narrowing down the potential cause. Going to book it in tomorrow and specifically request they check the transmission pressure sensor along with running their standard diagnostic tests. Appreciate the detailed insights and cost breakdown, helps set realistic expectations for the repair.