Audi S1 Starting Issues Linked to Terminal 30 Voltage

Had a very similar issue with my 2016 Audi A1. As someone with some hands-on experience working on cars, this sounded immediately familiar. The main symptoms match exactly, poor cranking and voltage drop during start attempts. After multiple failed attempts to diagnose it myself using a multimeter, I took it to a workshop. They performed a complete charging system diagnostic which revealed heavy battery discharge despite the battery testing okay initially. The workshop ran several tests: Full electrical fault scanning, Detailed voltage drop test across all terminals, Parasitic draw test, Alternator output verification, Ignition switch resistance check Turned out the battery was internally damaged despite showing acceptable voltage when tested statically. The power supply would drop significantly under load during starting. Total repair including diagnostics and a new battery came to 290 Euro. Before suggesting specific solutions, could you share: How old is your current battery? Do you notice any electrical issues when the engine is running? Have you had any recent electrical accessories installed? Does the problem occur more after the car sits unused? This information would help determine if youre facing the same root cause or if theres another electrical fault at play.

Thanks for the detailed response. Just had my service at 58998 KM. Let me address your questions: Current battery is original from 2018. The wiring harness and all electrical components work fine once running. No aftermarket accessories installed. The starting issue is definitely worse after sitting 2-3 days. Based on your experience, this does sound similar. The voltage drop pattern matches exactly what Im experiencing. Will have the workshop do a complete charging system diagnostic, focusing on the battery load test you mentioned. Thanks for breaking down the testing process. Helpful to know what to expect cost-wise for troubleshooting these electrical faults.

Thanks for the additional details. After reading your response, I'm even more convinced you're dealing with the same battery degradation issue I had with my A1. The age of your battery (5+ years) combined with the increased starting difficulty after sitting idle are classic indicators. The wiring harness and charging system working fine while running, but struggling during cold starts, mirrors my experience exactly. My battery also passed basic voltage tests but failed under load testing. Some key points from my repair experience: Original equipment batteries typically last 4-6 years, The fuse box and circuit connections tested fine, Short circuit testing showed no parasitic drain, Battery load testing revealed the actual issue If you want to avoid unnecessary diagnostic costs, request a specialized battery load test first. The complete charging system diagnostic might not be needed if the battery fails the load test. For reference, battery replacement alone cost about 190 Euro at the time, significantly less than a full system diagnostic. The original diagnosis pathway I took was more expensive because we tested everything before confirming the battery was the culprit.

Based on all your input regarding my 2018 S1, I really appreciate the thorough feedback on the battery situation. Looks like my 5-year-old original battery is the likely culprit, especially given the voltage drop during starts and problems after sitting idle. The timing makes sense, right in that 4-6 year window when the power supply typically starts failing. Will skip the full charging system diagnostic for now and start with the battery load test you suggested. Could save me quite a bit compared to the 290 Euro you spent on complete diagnostics. Think I will schedule the battery test this week while the ignition switch and starting issues are still manageable. Rather handle it now than risk being stranded with a complete failure. The 190 Euro estimate for just the battery replacement seems reasonable. Thanks for helping narrow down the problem. Will update once I confirm if its indeed a failing battery causing these voltage drop symptoms.