RS6 No-Start: Terminal 15 Ignition Signal Issue

Had a similar situation with an A6 3.0 TFSI from 2012. The symptoms matched exactly, starter motor turning but engine not firing up. Initially suspected the starter solenoid, but diagnostic testing revealed an ignition switch malfunction. The voltage drop test showed irregular current flow through Terminal 15. The root cause was a damaged circuit break between the ignition switch and the engine control module. The connection had deteriorated over time, creating intermittent contact issues. This is a serious problem that requires proper diagnostic equipment to pinpoint. The fuse box check alone is not sufficient, as the issue often lies in the wiring harness or ignition switch components themselves. The repair involved replacing the complete ignition switch assembly and rewiring several connections. Most important was verifying the proper voltage at all terminals after the repair. This is not a DIY job due to the complexity of the security systems in these models. Would strongly suggest having a certified shop perform a full diagnostic before replacing any parts. Unusual repairs without proper testing could lead to more expensive damage to the electrical system.

Thanks for the detailed explanation. Your issue sounds almost identical to what I experienced with my RS6 last winter. After the battery terminal check showed no issues, my mechanic also found problems with the wiring harness near the ignition switch. Ended up needing a complete relay switch replacement along with some rewiring work. Just curious, do you remember the total repair cost? Also, has everything been running smoothly since the fix? My repair bill was quite steep but wondering if it was in the normal range for this type of work.

Glad to help follow up. Just had my car back from the mechanic yesterday actually. The Terminal 15 ignition positive issue was indeed the culprit, just like in your case. The power supply interruption was traced to a faulty connection in the wiring harness. The repair cost came to 95 Euro for fixing the cable connection, which sounds much more reasonable than your complete relay switch replacement. The circuit break was simpler than initially feared, just needed to repair a compromised wire connection rather than replace the entire assembly. Everything has been running perfectly since the fix. No more issues with the car not starting, and all electrical systems are functioning normally. The mechanic mentioned these connection problems are fairly common in these models as they age, especially around the ignition components. Would suggest keeping the repair documentation, as similar issues can sometimes pop up again if other parts of the wiring harness start showing wear. Regular voltage checks during maintenance can help catch potential problems early.

After getting all the advice, I finally went ahead and got my RS6 fixed last week. The mechanic found the exact issue, a failing relay switch causing power supply problems. The starter solenoid was getting intermittent voltage, explaining why the motor would turn but not start the engine properly. The total repair came to 780 Euro, which included replacing the ignition switch assembly and fixing some damaged wiring. Initially thought it was steep, but given the complexity of the electrical system and the amount of diagnostic work needed, it makes sense. Car starts perfectly now and all electrical systems are working as they should. The voltage drop tests show normal readings across all circuits. Definitely worth getting it done properly rather than trying cheaper shortcuts that could have caused more problems down the line. Lesson learned, when dealing with electrical issues, best to have proper diagnostic testing done first rather than just replacing parts and hoping for the best.