VW Touran Weak Starting Traced to Terminal 30 Issue

Had nearly identical issues with my 2019 Tiguan last winter. Have some experience working on VW electrical systems, though I usually leave the complex stuff to professionals. The symptoms matched yours exactly, sluggish starter motor engagement despite a seemingly good battery. After the voltage drop got worse, I had it checked at a workshop. Their diagnostic revealed the battery was internally defective despite showing acceptable voltage readings on basic tests. The electrical fault was causing inconsistent power delivery to the starter circuit. The workshop performed a full charging system analysis and found: Battery cell damage, Slight corrosion on terminal connections, Circuit breaker was functioning properly, No ignition switch issues Total repair was 290€ including: New battery installation, Terminal cleaning, System diagnostic, Testing all related fuses and connections To better assist, could you share: Does the issue happen more after the car sits unused? Are there any warning lights on the dash? Have you noticed dimming headlights or other electrical issues? What were the exact voltage readings you measured? A proper diagnosis is important since starting problems can have multiple causes in modern vehicles. Would recommend getting it checked soon before you end up stranded.

Last service was at 65000km and everything appeared normal. Since posting my starting issue has gotten worse, especially when the engine is warm. The voltage readings were 12.4V at rest and 14.2V while running. No warning lights and no other electrical problems noticed so far. The issue does seem more pronounced after sitting for a few hours, particularly in warmer weather. Had the battery load tested at a parts store and it passed, but the short circuit test showed some inconsistent readings. After checking the wiring near the fuse box, I noticed one of the main power cables has some slight discoloration at the terminal. Will have the charging system thoroughly checked since your experience suggests these symptoms need professional diagnosis despite battery appearing ok. Thanks for the detailed response, especially the workshop findings. Good to know about checking for terminal corrosion as a potential factor.

Thanks for the follow-up details. The symptoms you describe, especially the warm engine starting issues and discolored power cable, remind me of what happened before my complete diagnosis. The voltage readings match what I saw too, technically acceptable but masking deeper issues. In my case, the voltage drop became more severe over 2-3 weeks. The discolored cable you spotted near the fuse box is concerning, on my Tiguan this was an early warning sign of resistance building in the charging system circuit. The workshop found this resistance was causing inconsistent power delivery to the starter motor. A key finding during my repair was that load testing alone wasnt reliable. The short circuit test showing inconsistent readings mirrors my experience, it points to potential internal battery damage that basic voltage checks miss. Since your symptoms are worsening with warm engine temperatures, I would prioritize getting it checked soon. In my case, delaying the diagnosis led to: Complete starting failure, Additional starter motor stress, Higher repair costs (490€ vs initial quote of 290€) The main battery cables and ignition switch should be thoroughly tested, given the pattern of intermittent issues and that visible terminal wear you noticed.

Your issue is definitely getting more serious and I appreciate the help and detailed repair info from your Tiguan experience. The wiring harness discoloration I found matches what you described, so that confirms my suspicion about a developing electrical fault. The voltage readings being similar to your case (12.4V/14.2V) but with inconsistent short circuit test results makes me think this could also be an internal battery issue despite passing the basic load test. Makes sense that the charging system needs proper diagnosis rather than just checking voltage. Will get it to a workshop this week before the warm starting problem gets worse. Dont want to risk damaging the starter or ending up with a 490€ repair bill like you mentioned. The fact that your terminal corrosion turned out to be connected to deeper charging system issues has convinced me to have everything thoroughly checked, especially those main power connections and ignition switch area where I spotted the discoloration. Thanks again for sharing such specific details about your repair experience. Really helped confirm that these symptoms need professional diagnosis despite the battery appearing ok on basic tests.