S6 Transmission & Starter Issues: Shift Lock Alert

As someone with some mechanical experience, I dealt with very similar symptoms on my 2011 A6 last year. The automatic transmission issues you describe match what I experienced, rough shifting, starting problems, and transmission-related codes. In my case, the transmission control unit was failing, causing communication issues between the transmission and engine systems. When the control unit starts going bad, it can prevent proper engagement of the neutral position safety switch, which explains why the car struggles to start even in park. The transmission repair took about 3 days at an independent specialist shop. Total cost was 1000 Euro for replacing and programming the control unit. Since then, the transmission has worked flawlessly with smooth shifting restored. Before you take it in, could you share: Current mileage, Exact transmission codes showing, Whether the problems started gradually or suddenly, If you notice any differences between cold and warm starts This info would help confirm if your S6 is facing the same transmission failure pattern. Getting it diagnosed early is critical, running with a faulty control unit can lead to more severe transmission damage over time.

Thanks for your detailed response. My current mileage is 134096 KM and the issues started quite suddenly about 2 weeks ago. The gear shifter feels noticeably different between cold and warm starts. When cold, it seems more resistant to move through the gears. The transmission sensor problems appear worse in the morning, with the shifting becoming slightly smoother after the car warms up. Still, the automatic transmission never feels quite right anymore. I will get the exact codes pulled again tomorrow and post them here. The initial scan definitely showed multiple transmission-related fault codes, but I want to be precise with the information.

Based on what you are describing, particularly the cold/warm behavior difference, this really does sound identical to my A6 transmission issues from last year. When my transmission acted up, it also showed those exact symptoms, especially that stiff gear shifter movement when cold. The fact that your automatic transmission performs better when warm points strongly toward the transmission control unit. These units often show early failure signs through temperature-dependent behavior. The transmission sensor network cant properly communicate position and shift data when cold. Since our cars are from the same generation and showing matching symptoms, I would bet you are dealing with the same root cause. My repair went like this: Full transmission diagnostic scan: 150 Euro, Control unit replacement: 700 Euro, Programming and coding: 150 Euro One tip from my experience, make sure they check the wiring harness connections during diagnosis. Sometimes corrosion at the transmission sensor plugs can mimic control unit failure symptoms. In my case, they cleaned all connections before confirming the control unit needed replacement. Keep us updated once you get those codes pulled. The specific transmission fault codes will help confirm if you are on the same failure path that my A6 went through.

Thanks for all the input. After getting the codes pulled again today, here are the main transmission-related ones: P0706, Transmission Range Sensor Circuit Range/Performance P0750, Shift Solenoid A Malfunction P1778, Transmission Control Unit Communication Error These codes plus the symptoms you described with your automatic transmission issues match my situation perfectly. The shift lock problems and rough shifting are exactly as you detailed. I called a transmission specialist shop and booked it in for next week. They quoted about 1100 Euro for diagnosis, control unit replacement, and programming if needed. The neutral position safety switch will also be inspected since that could be contributing to the starting problems. Will post an update once the repair is complete to confirm if it was indeed the transmission control unit. Really hoping this fixes both the shifting and starting issues without needing more extensive transmission repairs.