VW Nivus Power Loss: ECU vs Mechanical Mystery

I had a very similar issue with my 2019 VW T-Roc. As someone with moderate experience in car maintenance, I initially thought it might be a simple computer module reset issue, but it turned out to be more complex. The symptoms matched yours exactly, reduced power, check engine light, and multiple error codes during car diagnostics. After trying basic troubleshooting, I took it to a workshop specializing in vehicle electronics. They discovered the main relay was defective, which was causing intermittent power supply issues to the ECU. The repair took about 2 hours and cost 120€, including parts and labor. Since the fix, all systems have been working perfectly, no more error codes or power issues. Before suggesting more specific solutions, it would help to know: Have you noticed any other electrical issues (flickering lights, inconsistent starting)? What specific error codes showed up in the diagnostic scan? Did these issues start suddenly or develop gradually? Are there any particular driving conditions when the problems occur more frequently? The automotive electronics in modern VWs are quite complex, so pinpointing the exact cause is crucial for an effective repair. Once you share these details, I can provide more targeted advice based on my experience.

Thanks for your thorough explanation. My Nivus has 107518km and the latest service was done in December. The electrical issues started gradually over two weeks. I checked the error codes again: P0685 and P0687, pointing toward ECU power control circuit issues. The engine performance problems mostly happen during highway driving after about 30 minutes. The check engine light flashes intermittently during these episodes. I tried a basic system reset using an OBD scanner, but the problems returned within a day. The vehicle electronics seem more unstable now, the infotainment system occasionally freezes and the engine control unit appears to be struggling to maintain normal operation. Your relay fix sounds promising since the symptoms match. Did you need to reflash the computer module after the repair? The engine performance issues are getting worse and Im hoping to avoid major repairs if possible.

Thanks for those additional details. After fixing the relay on my T-Roc, no ECU reflash was necessary. The system reset itself once the proper power supply was restored to the computer module. Your error codes P0685 and P0687 are exactly what my vehicle showed, classic signs of power supply problems affecting engine performance. The fact that your issues worsen during extended highway driving suggests heat might be amplifying the relay problem, which matches my experience completely. The freezing infotainment system and unstable engine control unit behavior are typical symptoms of voltage irregularities. Before my repair, these automotive electronics issues would get progressively worse, especially in hot weather or during longer drives. A few quick checks you can do: Check battery terminal connections for corrosion, Test battery voltage during idle and while driving, Listen for clicking sounds from the main relay area when starting the car Since your symptoms are nearly identical to what I experienced, focusing on the main relay would be a good starting point. The relatively low repair cost (120€ in my case) makes this worth investigating before considering more extensive ECU problems or engine performance repairs. Would recommend getting this checked soon, as continuing to drive with unstable power supply could potentially cause more extensive damage to other electrical components.

Thanks for that detailed feedback. I checked my connections and battery voltage as suggested, all looks normal, but I did notice a faint clicking sound from the relay area on startup that I hadnt caught before. Given how closely your experience matches my issues, especially with the highway driving problems and matching error codes, Im going to have my local shop check the main relay first. The car diagnostics they ran previously didnt specifically focus on the power supply circuit, so this gives them a clear direction to investigate. The repair cost you mentioned is much more reasonable than I feared. Initially, I was worried about extensive ECU repair or complete replacement, which would have been significantly more expensive. If the vehicle electronics are just suffering from an unstable power supply via a faulty relay, that would explain all my symptoms, from the engine performance issues to the glitchy infotainment system. Will book it in tomorrow and have them focus on checking the main relay and surrounding circuit. Hopefully, this relatively simple fix will resolve all these issues like it did in your case. Will update once I know more.