Slow S5 Starter Motor Points to Terminal 30 Issue

Had nearly identical issues with my 2016 Audi S4. Started with sluggish cranking and got worse over time. As someone with some hands-on experience working on cars, I first suspected similar causes. Despite normal voltage readings, my battery ended up being the root cause. The workshop discovered that while voltage looked fine at rest, it dropped significantly under load, indicating internal cell damage. A proper load test revealed the battery was only delivering about 30% of its rated cranking power. The diagnostic process involved: 1. Full electrical system scan 2. Load testing the battery 3. Checking for voltage drops across the wiring harness 4. Testing the starter circuit for any short circuits 5. Inspecting all fuse box connections Total repair cost was 290 Euro, which covered: New battery, System diagnostic, Battery registration/coding For your S5, would be helpful to know: Age of current battery, Any warning lights on dash, Whether issues happen more after short trips, If electrical accessories work normally The symptoms match exactly, but would need these details to be more certain about the diagnosis. Have you had a proper load test done on the battery rather than just checking voltage?

Thanks for the detailed explanation. Just had my latest service at 176114KM. The workshop went through the charging system thoroughly and found a bad ground connection at the starter motor, plus some corrosion on the main power cable terminal. Was definitely causing voltage drop under load. After cleaning all connections and replacing the corroded terminal, the starting is back to normal. They also tested the circuit breaker and fuse box connections while diagnosing the electrical fault. Total repair was 180 Euro including labor. Good to know about checking the battery under load, will keep that in mind for future troubleshooting. The slow cranking symptoms can really trick you into replacing parts unnecessarily if you dont track down the root cause of the short circuit first.

Thanks for the update on your S5 starting issue. This matches what I discovered with my S4 after diving deeper into similar symptoms. Poor connections causing voltage drop are often overlooked when diagnosing starting problems. While my initial thought was battery-related, finding those bad ground connections and corrosion points is crucial during electrical fault diagnosis. My S4 actually had similar corrosion buildup at the starter motor connections that I found later, though not as severe as yours. The repair cost was reasonable at 180 Euro considering the diagnostic work needed to trace voltage drop issues in the starting circuit. Much better than unnecessarily replacing the starter motor or other components. One tip: since fixing my ground connections, I now do regular checks of the power supply points and terminals as preventive maintenance. Helps catch corrosion before it affects the ignition switch and starter circuit performance.

Thanks for sharing your experience. After seeing similar cases, its worth noting that voltage drop from bad connections is more common than many realize. The workshop found our issues had the same root cause, poor ground connection and corrosion affecting the starter motor circuit. For others reading: these symptoms can mask themselves as battery or starter motor problems. Getting a proper diagnosis of the charging system saved replacing expensive parts unnecessarily. The wiring harness connections, especially grounds, should always be checked first. In my case, cleaning the connections and replacing the corroded terminal at 176114KM fixed it completely. Total cost was 180 Euro including labor to trace the short circuit through the fuse box and test all connections. The starter motor now engages instantly every time. Regular inspection of these connection points is now part of my maintenance routine. Much cheaper than waiting for starting problems to develop from corroded terminals causing voltage drop issues.