Audi S8 Starter Issues Linked to Terminal 30 Circuit

Having dealt with a similar starting issue on my 2011 Audi S6, I can share some relevant experience. Based on some experience with electrical issues, this sounds familiar. After installing a new battery and still having problems, my workshop went through a systematic diagnosis: 1. Checked all connections in the fuse box, particularly the main power distribution points 2. Tested the starter motor for proper current draw 3. Examined the ignition switch circuit 4. Performed voltage drop tests across all major connections 5. Inspected the main ground straps The root cause turned out to be corrosion at the main power distribution point in the fuse box, creating resistance in the circuit. The workshop did a complete cleaning of all terminal connections and replaced several corroded components, costing 290 Euro in total. Before suggesting specific fixes, could you share: Any error codes showing up? Does the problem occur more often when the engine is hot or cold? Have you noticed any other electrical issues like dim lights or slow power windows? Did you check for parasitic draw that might be draining the battery? A proper diagnosis should include checking the entire circuit from battery to starter motor, including all ground connections and the main power distribution points.

Last service was completed at 152400km where they performed standard maintenance and noted no electrical issues. After cross checking my symptoms with a repair manual, the sluggish starter motor behavior seems consistent with a failing circuit breaker rather than the starter itself. The voltage readings at the battery show 12.6V but drop significantly during cranking, suggesting high resistance somewhere in the wiring harness. I have started checking the main power connections at both battery terminals and will methodically work through the ignition switch wiring next. No corrosion visible at any accessible points so far. Good to know about checking the distribution points in the fuse box, will add that to my inspection list. The new battery was tested and confirmed good, so focusing on tracking down the electrical fault in the starting circuit seems like the logical next step before replacing any major components.

Thanks for the additional details about your starting issues. After dealing with similar problems on my S6, the voltage drop during cranking definitely points toward a high-resistance connection in the charging system. A few specific points from my experience: The circuit breaker issue you mentioned matches what I found, my workshop detected a failing breaker that was causing intermittent voltage drop under load, Even with clean-looking terminals, micro-corrosion can create enough resistance to affect the power supply, When my fuse box was inspected, several connection points showed heat damage that wasnt visible externally Something else to check, my car had an electrical fault where the alternator wasnt properly maintaining charge during short trips. This put extra strain on the battery despite showing good voltage at rest. Before going further, try this quick test I learned: 1. Use a multimeter to check voltage at battery terminals during cranking 2. Compare to voltage reading directly at the starter 3. More than 0.5V difference indicates a problem in the circuit The systematic approach youre taking helped identify my issues without replacing unnecessary parts. Let me know what you find with the ignition switch wiring, that was a common failure point in these models.

Thanks for the detailed troubleshooting suggestions. After performing the voltage drop test you recommended, I found a 0.7V difference between the battery and starter motor terminals during cranking. This definitely confirms a high resistance problem in the charging system circuit. Spent today checking the power supply path from battery to starter. The starter solenoid tested fine, but noticed some discoloration on the main circuit breaker housing. Going to replace that component first since its consistent with the symptoms and the voltage readings. The ignition switch wiring harness looks intact with no obvious damage, though I plan to trace those connections fully once I verify if the circuit breaker resolves the sluggish starting. At least the alternator seems to be working properly based on charging voltage readings while running. Makes sense about hidden corrosion in the fuse box connections, will keep that in mind if the starting issue persists after the circuit breaker replacement. Trying to avoid throwing parts at it without proper diagnosis, so taking it step by step through the power supply path.