A8 Diesel: Total Ignition Failure at Terminal 15

Had a similar situation with my 2015 A6 3.0 TDI. The symptoms matched exactly, complete failure to start with no response when turning the ignition switch. The issue traced back to a faulty starter solenoid and corroded battery terminals. The starter solenoid was not receiving the activation signal from the ignition switch due to a circuit break in the wiring harness. The corrosion on the battery terminals made the problem worse by preventing proper current flow. The repair involved: Cleaning and securing all battery terminal connections, Replacing the starter relay switch, Repairing damaged wiring to the starter solenoid, Testing the ignition switch circuit This was a significant repair requiring specialized diagnostic equipment. The combination of electrical issues meant the car needed to stay at the shop for proper testing. While not the most complex repair, it required careful troubleshooting to identify all failing components. Would recommend having it checked soon, as continuing to try starting with faulty electrical components can cause additional damage to the starting system.

Thanks for sharing the details about your A6 electrical problems. Your case sounds really similar to what my A8 was doing. The complete power failure and ignition switch problems match up. After reading this, I checked the battery terminals and found some corrosion too. Before I take it to a shop, could you remember roughly how much the total repair cost? Also curious if youve had any other electrical issues pop up since getting it fixed? The fuse box and power supply systems in these cars can be tricky, so Im trying to gauge if I should expect more problems down the line.

The total repair at my shop came out way lower than expected, just 95 Euro to fix a cable connection issue with Terminal 15 ignition positive. The mechanic found the problem quickly in the wiring harness and managed to repair the connection without needing to replace major components. Havent seen any other electrical problems since the repair was done 8 months ago. The power supply system and ignition switch are working perfectly now. Initially was worried it might need a new fuse box or extensive rewiring, but the issue was isolated to that one faulty connection. My advice would be to have your battery terminals cleaned and checked first, then let them diagnose the ignition circuit. Could save you money if its a similar simple fix rather than jumping straight to replacing expensive components. Just keep in mind relay switch issues can sometimes mask themselves as bigger problems, so proper diagnosis is key. Regular electrical system checks have helped prevent any new issues from developing.

Glad I asked about your experience before rushing to the shop. After your reply, I decided to get it checked out. Turns out the issue was pretty similar to yours, a faulty connection in the wiring harness near the relay switch was causing the starting problems. The total repair came to 120 Euro, mostly labor costs for tracking down the exact point of the circuit break. They also cleaned up the battery terminals while they had it open. The mechanic showed me where the wiring had worn through, apparently a common issue in these models. The fix took about 2 hours and they did a full system check through the fuse box to make sure there werent any other electrical gremlins hiding. Car starts perfectly now, and Ive learned my lesson about regular electrical system maintenance. Really appreciate the detailed info you shared, it helped me understand what I was dealing with and probably saved me from getting oversold on unnecessary repairs.