Audi Q5 Cranking Issues Point to Terminal 30 Circuit

As someone with some experience working on Audis, I faced a very similar electrical fault with my 2018 Audi Q3 2.0T. The symptoms matched yours exactly, slow cranking and multiple start attempts needed. Initially, the charging system seemed fine with basic testing, but the workshop found the real issue using advanced diagnostics. Despite having a new battery, there was a faulty circuit breaker causing intermittent connection problems in the wiring harness. This created voltage drops that affected the whole electrical system. The complete diagnosis involved: Full electrical system scan, Testing the ignition switch connections, Voltage drop testing across all major circuits, Inspection of the main power distribution points The repair cost me 290 Euro, including parts and labor. The fix involved replacing the circuit breaker and cleaning all terminal connections in the charging system pathway. Before suggesting more specific solutions, could you share: Any warning lights on the dash? Does this happen more often after the car sits unused? Have you noticed any other electrical issues like dim lights or radio problems? Did you get the battery tested under load? This information would help determine if your issue matches what I experienced or if its something else in the electrical system.

Latest service was at 25000 KM. Thanks for the detailed response. My Q5 actually started showing these symptoms right after it got wet during a heavy rain storm. No warning lights on the dash, but I did notice the headlights seem slightly dimmer when trying to start. The starter motor sounds different than usual, more labored and sluggish. A voltmeter test showed 12.6V at the battery terminals, but I havent done a load test yet. Nothing unusual with other electronics, and the problem occurs regardless of how long the car sits. Have arranged for the dealer to check the fuse box connections since water exposure could have caused corrosion there. Still waiting on the full diagnosis but would prefer to avoid replacing the whole wiring harness if possible.

I understand your situation, especially after my experience with water damage on my Q3. The symptoms after rain exposure strongly point to moisture-related issues in the power supply system, similar to what I dealt with. After my initial circuit breaker replacement, I discovered corrosion had spread further than first apparent. The voltage drop you mentioned with the headlights during starting matches exactly what I experienced. A key detail I didnt mention in my first response, the electrical fault was traced to water intrusion at the main power distribution block. Some critical points from my experience: The 12.6V reading at rest is normal, but voltage drops under load are the real concern, Moisture typically affects multiple connection points, not just the fuse box, The ignition switch connections are particularly vulnerable to corrosion, Cleaning and resealing connections often fixes the issue without harness replacement The repair on my Audi ended up costing 450 Euro total, as we found additional corroded terminals during the complete diagnosis. The fix included: Cleaning all power distribution connections, Applying dielectric grease to prevent future corrosion, Resealing vulnerable entry points, Installing additional moisture barriers A full harness replacement wasnt necessary in my case, and likely wont be in yours based on the similar symptoms.

Based on the conversation flow, here is my reply as: Thanks for sharing those extra details about your Q3 repair. The water-related problems you described sound exactly like what I'm dealing with. Really hoping my fix will be as straightforward as yours without needing the full harness replacement. The sluggish starter motor behavior definitely matches what you experienced. After checking the voltage drop during starting, it reads 10.2V which seems to confirm the electrical fault hypothesis. The dealer found some visible corrosion near the main power distribution block, just like in your case. Going to have them do a complete terminal cleaning and sealing service first. The 450 Euro repair cost you mentioned seems reasonable compared to a full harness replacement. They quoted around 400 Euro for the initial diagnostic work and basic repairs, so that tracks with your experience. Will update once I know if cleaning the connections and adding moisture protection resolves the voltage drop issues. Thanks again for the detailed walkthrough of your repair process, its given me a much better idea of what to expect.