SQ5 Starting Issues: Charging System or Bad Switch

Had the exact same symptoms on my 2014 S4 last winter. The initial signs pointed to a faulty battery, but it turned out to be more complex. The main issue was a compromised wiring harness near the starter motor, causing an intermittent short circuit. The power supply was inconsistent due to corroded connections at terminal 30, which connects directly to the battery positive terminal through the fuse box. After thorough diagnosis, we found that water had seeped into the main electrical connection points, causing corrosion. The fix required: Complete wiring harness replacement near the starter, New battery terminals, Cleaning of all ground connections, Testing the charging system This was a serious electrical fault that could have left the car stranded if not addressed. The alternator was actually fine, despite initial suspicions. Recommend having these checked: 1. Battery load test 2. Voltage drop test at terminal 30 3. Starter motor connections 4. Full scan for any stored fault codes 5. Visual inspection of the wiring harness for signs of wear The unusual starting issues are often misdiagnosed as just a battery problem, but with these symptoms, its likely a combination of electrical issues.

Thanks for sharing your experience. Your detailed explanation matches a lot of what I am seeing with my SQ5. Especially interesting about the wiring harness issue, as I noticed some unusual wear near the engine bay. I am going to have all those points checked at another workshop. Really good to know about the possible water damage to the circuit breaker area, makes sense given the symptoms. Could you remember roughly how much the complete repair cost you? Also, have you had any other electrical gremlins pop up since the fix?

Since getting my S4 repaired, the electrical system has been rock solid with no new issues emerging. The Terminal 30 continuous plus interruption was completely resolved after the fix, which was a relief given how frustrating those starting problems were. The total repair came to 290 Euro, which covered fixing the heavily discharged battery and related electrical components. This might seem steep, but considering the complexity of modern vehicle electrical systems and the potential for a complete breakdown, it was worth every cent. The key was finding a workshop that properly diagnosed the voltage drop and traced it through the entire circuit breaker system. A lot of shops might have just replaced the battery without addressing the underlying wiring harness issues. The thorough approach prevented any recurring problems with the power supply. Just make sure your new workshop does a complete electrical diagnostic, not just surface-level checks. The intermittent nature of these issues means they need to inspect the entire electrical pathway from battery to starter.

Thanks everyone for your input. Finally got my SQ5 sorted after taking it to a different workshop. Turned out to be exactly what was suggested, a damaged wiring harness combined with corrosion at terminal 30. The mechanic found water had been seeping in through a damaged grommet, causing havoc with the circuit breaker and nearby connections. Total repair came to 340 Euro, including a thorough electrical fault diagnosis, new wiring harness section, and cleaning of all connections. The voltage drop test revealed multiple weak points that needed addressing. They also found and fixed a small short circuit near the fuse box that the previous shop had missed completely. Car starts perfectly now. The workshop showed me all the damaged parts and explained how the electrical system works together. Really glad I got a second opinion rather than just replacing parts out of nowhere. Definitely learned to pay more attention to unusual electrical symptoms early on.