Audi A7: Terminal 15 Switch Halts Engine Start

Just went through a similar situation on my 2017 Audi A5. The no-start symptoms matched exactly: no crank, stored error codes, and terminal 15 power issues. The root cause turned out to be a combination of corroded battery terminals and a faulty starter solenoid. The wiring harness connecting to the ignition switch was intact, but the relay switch had degraded connection points. The proper diagnosis requires testing the power supply circuit systematically. When the starter solenoid was tested, it showed intermittent voltage drops. This can be misleading since it mimics ignition switch failure symptoms. This ended up being a serious electrical system issue that required: Complete battery terminal cleaning and replacement, New starter solenoid installation, Relay switch replacement, Full circuit testing Important: Simply replacing the ignition switch without checking these components often leads to recurring issues. A complete power supply diagnostic is essential for a lasting fix. The repair was labor intensive due to access requirements, but addressed the root cause rather than just treating symptoms.

Thanks for sharing your experience. What you described matches my issues nearly perfectly, including the misleading voltage drops at the starter solenoid. The fuse box connections all tested fine, but we ultimately found similar problems with the relay switch and wiring harness assembly. Would you mind sharing what the total repair cost was in your case? Also curious if youve had any electrical gremlins pop up since the fix was completed. My A7 is scheduled for repair next week and Im trying to budget accordingly.

Since getting my A5 fixed at the shop, the Terminal 15 ignition positive issue was completely resolved with a repair to the faulty cable connection. The final cost came to 95 Euro for the wiring harness repair work. I can confirm there have been zero electrical problems in the months following the fix. The voltage drop issues that were misleading us initially are completely gone. The circuit break that was causing the no-start condition turned out to be much simpler than expected, just a damaged connection point where the power supply feeds into the ignition system. For your A7, since the symptoms match so closely, you might be looking at a similar straightforward fix. The key was having the mechanic properly trace the full power supply path rather than just replacing parts. Make sure they thoroughly check all battery terminal connections during the diagnostic process.

Thanks everyone for the detailed help. Finally got my A7 back from the shop yesterday. The car won't start issue was resolved after they found multiple problems in the electrical system. The mechanic performed a complete circuit analysis and discovered a failing starter solenoid along with some corroded connections. The total repair came to 850 Euro, which included: New starter solenoid, Power supply wiring repairs, Labor for complete diagnostic testing, Cleaning all battery terminals The voltage drop issues completely disappeared after the fix. The mechanic explained they had to trace the entire circuit to find all the weak points rather than just replacing the obvious parts. Really glad I pushed for a thorough diagnosis instead of accepting the first attempted repair. The car starts perfectly now. No more electrical issues or error codes showing up. This experience taught me to always insist on proper diagnostic testing when dealing with electrical problems.