VW T-Roc Starting Issues: Terminal 30 Power Problems

Had a similar issue with my VW Tiguan (2017, gasoline). The symptoms you describe match exactly what I experienced, slow cranking and occasional no-start conditions despite a new battery. With some experience working on VW electrical systems, I first suspected a faulty starter motor. However, the workshop diagnosed a voltage drop in the main power circuit, caused by corroded connections at the terminal block. They also found an electrical fault in the circuit breaker that protects the starter circuit. The fix involved: Cleaning and securing all battery connections, Replacing the main terminal block, Installing a new circuit breaker, Testing the complete charging system Total cost was 290€ and the issue has not returned in 8 months. Before suggesting more specific solutions, could you share: Does the problem occur more often after short trips? Have you noticed any warning lights on the dash? When was the last time the starter motor was checked? Did you measure the voltage at the battery during cranking? The fuse box connections should also be inspected, as they can cause similar symptoms when corroded. Would be happy to provide more detailed guidance once you share those details.

Mileage update at 76699km and latest service was in January. After the voltage drop issue was identified, I can confirm the problem persists despite testing other components. The starter motor spins properly now after cleaning the main power connections, but the occasional no-start condition remains. The workshop did find corrosion in the fuse box near terminal 30, and while they cleaned it, I wonder if there might be a deeper wiring harness issue. The ignition switch readings are normal, but we detected inconsistent voltage when testing different connection points. The problem definitely occurs more after rain, suggesting water might be getting into a connector somewhere. No warning lights appear on the dash during these episodes.

Thanks for the additional details about your T-Roc's starting issues. On my Tiguan, I also noticed the problem was worse in wet conditions, which turned out to be a key diagnostic clue. After the initial repairs I mentioned, we eventually traced the intermittent no-start to water infiltration around the firewall wiring grommet. The water was causing corrosion inside the main power supply harness, creating a hidden voltage drop that wasnt immediately obvious. The permanent fix required: Replacing the entire wiring harness section from battery to starter, Installing upgraded waterproof connectors, Resealing the firewall penetration points, Adding protective covering on exposed wiring sections The repair cost 480€ but completely resolved both the voltage drop and intermittent starting issues. The electrical fault hasnt returned even in heavy rain. Since your symptoms match so closely and worsen with moisture, I strongly suspect your ignition switch circuit is experiencing the same type of water-related degradation. A circuit breaker replacement alone wont fix this if water is getting into the harness. Consider having the workshop specifically check: Firewall wiring grommets for water intrusion, Harness insulation condition along its entire run, All ground connection points for hidden corrosion

The problem seems to be progressing just like yours did. Looking at my maintenance records from January, there have been 21 no-start events, with 15 occurring during or after rain. The voltage readings are exactly what you described, inconsistent at different test points along the circuit. I checked the firewall area you mentioned and found signs of water tracking along the wiring harness. The charging system tests normal when it does run, but the electrical fault appears unusual until you consider the moisture correlation. Based on your experience, I will have the workshop do a complete inspection of the wiring harness and replace any compromised sections. The circuit breaker and ignition switch can test fine individually while the real problem hides in corroded connectors or damaged insulation. Planning to schedule the repair next week and will document all the replaced components. Really helpful to know the approximate cost range too, gives me a good reference point when discussing the work scope with the workshop.