VW Lupo Diesel No-Start: ECU Control Light Issues

I had a very similar issue with my 2007 VW Polo diesel last winter. Being somewhat experienced with basic car maintenance, I first thought it was an engine fault related to the ECU. After checking the obvious things like you did (battery, fuses), I took it to a workshop for proper engine diagnostics. Turns out the battery connections were corroded and not making proper contact, despite the battery itself being fine. The engine control light was staying on because the system wasnt getting consistent power. The fix was actually quite simple. The workshop cleaned all battery terminals and connectors, applied anti corrosion coating, and properly retightened everything. Total cost was 155€ including the diagnostic scan. The engine surge and starting issues disappeared completely after this. Before suggesting more specifics, could you share: Any recent work done on the electrical system? Does the dashboard light up normally when you turn the key? Have you noticed any fuel injection related issues before this started? Are there any other warning lights besides the check engine light?

Latest service was just completed at 95355km. Your electrical system theory makes perfect sense. I double checked the battery connections this morning and noticed some white crusty residue on the negative terminal. This could definitely explain the engine control light and no start condition. Just to clarify some of your questions: No recent electrical work, dashboard lights up normally, and no prior fuel injection problems. The check engine light is the only warning showing. Think I will start by properly cleaning those battery connections. If the issue persists, I may need that professional ECU diagnostic scan to rule out any engine software issues. Would rather fix corroded connections than face a full ECU failure. Thanks for the detailed response. The 155€ repair cost seems very reasonable compared to replacing electronic components.

Thanks for providing those extra details, that white residue you found is a classic sign of battery corrosion that can trigger the check engine light and cause starting problems. Definitely clean those connections first. With my Polo, I learned that even a seemingly minor connection issue can make the ECU act up. After fixing the battery terminals, I also had the workshop update the engine control software since they were already doing the diagnostics, might be worth considering if cleaning alone doesnt solve it. The identical service interval on my Polo (95000km) actually revealed some hidden electrical gremlins that were affecting the engine control systems. The battery connection cleaning fixed most issues, but they also found a loose ground wire near the starter that was contributing to intermittent engine stalling. Keep us posted on whether the battery terminal cleaning resolves the engine fault. If you do end up needing that diagnostic scan, make sure they check all ground connections too, its often overlooked but crucial for proper ECU function.

Thanks for the helpful advice. Just wanted to update that I followed the suggestion about cleaning the battery connections and it actually solved the problem. After removing all that corrosion and properly reconnecting everything, the engine control light went off and the car starts perfectly now. For anyone searching with similar issues, definitely check those battery connections before assuming engine software or ECU problems. Saved myself a lot of money by starting with this simple fix rather than jumping straight to expensive engine diagnostics. No need for that 155€ repair bill yet, though I might still get the engine control system checked during the next service just to be safe. Much rather catch any developing issues early than face a complete engine fault down the road. Really appreciate the detailed troubleshooting steps everyone shared. Sometimes the simplest solution is the right one!