Audi A4 Slow Start Despite Good Battery, Terminal 30 Issue

Working as a general mechanic and having some experience with VAG cars, I dealt with a very similar issue on my 2008 Audi A3 2.0T. The symptoms were nearly identical to what you describe. Initially, I also thought the battery tested fine, but it turned out the short circuit test revealed internal damage. The workshop found that while the battery showed adequate voltage, its actual capacity was severely compromised. The failing battery was causing unusual voltage drops, which made the ignition switch and wiring harness connections appear faulty. The diagnostic process involved: 1. Checking all fuse box connections 2. Testing voltage at various circuit points 3. Load testing the battery under different conditions 4. Inspecting the main wiring harness for potential damage The final fix was straightforward, replacing the battery (290 Euro including diagnostic time). After replacement, all starting issues disappeared completely. Before suggesting more specific solutions, could you share: Have you noticed any electrical issues before the starting problems began? Does the problem occur more frequently after short drives? What was the exact method used to test your battery? Are there any warning lights on the dashboard? This would help determine if your issue matches what I experienced or points to a different root cause.

Thanks for checking, did the complete battery voltage drop test and replaced the main 40A fuse in the fuse box last week at 59303 KM. The wiring harness appears intact with no visible damage. The voltage readings are stable at the circuit breaker points, so I am more convinced it might be the ignition switch itself. When testing the continuous power supply at Terminal 30, I get inconsistent readings which could explain the intermittent starting issues. The last service was done a month ago and they found no major electrical faults. Will try testing voltage at different ignition switch positions next to narrow down the issue. Has anyone successfully diagnosed a similar problem by checking the ignition switch resistance values?

Based on my experience with the same issue on my A3, checking the ignition switch resistance is a good next step, but I found Terminal 30 inconsistent readings can also point to a failing starter motor solenoid. After dealing with similar symptoms, I discovered that stable voltage at circuit breaker points doesnt always tell the full story. In my case, the power supply showed normal readings until tested under actual starting load conditions. The voltage drop became significant only during cranking. What helped diagnose my issue was: 1. Testing voltage at Terminal 30 while cranking 2. Measuring resistance across the starter motor solenoid 3. Checking for voltage drop in the wiring harness under load The starter motor ended up being the culprit, though the symptoms initially pointed to the ignition switch. The repair cost was 450 Euro including parts and labor. Before replacing the ignition switch, consider having the starter motor thoroughly tested. The intermittent nature of your starting issues matches what I experienced with a failing starter solenoid rather than a faulty ignition switch. Would you be able to measure the actual voltage drop during cranking? This would help confirm if its following the same pattern I encountered.

Thanks for the detailed insight. Makes sense about testing under actual load conditions. I hooked up my multimeter during cranking and found significant voltage drops, down to 8.7V when attempting to start. This definitely aligns with your starter motor diagnosis rather than my initial ignition switch theory. The short circuit test on the starter solenoid showed resistance values outside spec, so youre likely right about the root cause. Given the electrical fault pattern matches your experience so closely, I will get the starter motor replaced rather than chasing an ignition switch issue. For others searching the forum, the key learning here is that stable voltage readings at the fuse box and charging system can mask problems that only show up under actual cranking load. The wiring harness checked out fine, but the real diagnostic clue was the voltage drop during starting attempts. Will update once I get the starter replaced. Any suggestions on testing procedures to verify everything is working correctly after the repair?