Audi A8: Terminal 30 Power Issues Plague Starting

Having some experience working on similar issues, I dealt with this exact problem on my 2013 Audi A6 3.0T last year. The symptoms you describe match perfectly with what I encountered. Initially thought it was just the battery, but the real culprit turned out to be a combination of issues in the charging system. The workshop found significant voltage drop across multiple connection points. The main issue was corrosion build-up at the battery terminals and a deteriorating ground strap, which affected the entire electrical system. The mechanic performed a complete electrical system diagnosis, cleaned all terminals, replaced the ground strap, and discovered a failing circuit breaker in the main fuse box. Total repair came to 290 Euro and solved the starting issues completely. Before suggesting specific fixes, could you provide: Current battery voltage readings (both engine off and running), Any warning lights on the dashboard, Whether the problem occurs more after the car sits for several days, If you notice dimming headlights or other electrical issues The ignition switch could indeed be part of the problem, but lets verify the basics first. These models have complex electrical systems, and proper diagnosis is crucial before replacing parts.

Last service done at 182484KM covering standard maintenance and electrical system check. After further inspection, I noticed that when wiggling the wiring harness near the main fuse box, the voltage readings fluctuate significantly. The terminals show signs of oxidation, and there appears to be a loose connection at one of the main power distribution points. Connecting a multimeter reveals unstable voltage when moving the harness, suggesting a short circuit somewhere in the main power distribution. This could explain the inconsistent Terminal 30 readings mentioned earlier. The charging system also seems affected as voltage drops below normal levels during starting. Will have the shop focus on tracing the wiring harness pathway and checking all connection points in the power distribution system. The symptoms definitely point toward a wiring issue rather than component failure.

Thanks for the additional details about the wiring harness inspection. Your findings strongly align with what I experienced, the voltage fluctuations when moving the harness are a telltale sign. In my case, after discovering similar unstable readings, the actual fix involved tracing the entire Terminal 30 circuit. We found multiple points where the insulation had worn through, causing intermittent contact with nearby metal components. The voltage drop was most severe where the harness passed through the fuse box mounting bracket. Some key points from my repair: The main power distribution block needed complete cleaning and reseating, Several corroded pins in the fuse box were replaced, A section of the harness required rewrapping due to damaged insulation, The ignition switch connections were cleaned and tightened The charging system returned to normal operation after addressing these issues. My voltage readings stabilized at 14.2V while running, and cold starts became consistently strong again. A thorough inspection of the entire Terminal 30 circuit path is definitely the right approach. Make sure the shop checks the starter motor connections as well, even though its new. Poor connections can mimic a failing starter. The repair cost ran about 450 Euro including parts and labor, but it completely resolved the starting problems.

Thanks for the detailed follow up on the voltage fluctuations. Those unstable readings when manipulating the wiring harness definitely validate my initial suspicions about a potential short circuit or connection issue. The oxidation around the terminals and loose connection at the power distribution point match exactly what my multimeter revealed during testing. With voltage dropping during startup and the charging system showing irregular behavior, I feel confident the issue lies within the main power circuit rather than individual components. Based on my Terminal 30 readings and the erratic behavior when moving the harness, I think focusing repair efforts on the wiring and connection points is the right approach. Will have the shop do a complete trace of the power distribution system, paying special attention to: All connection points showing signs of oxidation, Areas where the wiring harness may be contacting metal, Main fuse box mounting points, Starter motor wiring despite it being new Seems the ignition switch is likely fine since the problems appear clearly linked to the harness and charging system issues I identified. Will update once the shop completes their diagnostic work and repairs. The specific voltage readings should help them pinpoint the exact location of the short circuit.