VW Lupo ECU Failure: Power Loss Symptoms & Solutions

Having encountered a similar issue with my 2003 VW Polo diesel, I can share my repair experience. I noticed comparable symptoms, reduced engine performance and stored error codes in the car diagnostics system. After initial troubleshooting attempts, a professional inspection revealed the main relay was defective, affecting the engine control unit functionality. The repair involved replacing the main relay rather than the complete ECU. The workshop performed a system reset after installation, which restored normal engine performance. The total cost was 120€, including diagnostic testing and parts. This fix proved more cost-effective than a full computer module replacement, which would have been significantly more expensive. The car diagnostics confirmed all error codes were cleared after the repair. To provide more specific guidance for your case, could you share: The exact error codes from your diagnostic scan, Whether the check engine light is constantly on or intermittent, If the power loss occurs gradually or suddenly, The current mileage of your Lupo This information would help determine if your issue matches the relay problem I experienced or points to a different ECU repair need.

Thanks for the detailed suggestion about the relay. Last service was done at 134604km and the mechanic did a full diagnostic scan showing P0401 and P0103 codes. The check engine light started flashing intermittently about 2 weeks ago, and power loss happens mostly during cold starts. Initially thought the mass airflow sensor was the culprit, but after cleaning it saw no improvement. The automotive electronics specialist I consulted mentioned potential ECU problems but wanted to run more tests. Going to have them check the relay connection points since your experience with that fix makes sense given the similar symptoms with the control system. Would you mind sharing how long the system reset procedure took at your workshop? Just trying to plan around potential repair times.

Glad my relay tip resonated with your situation. For my Polo, the entire diagnostic and repair process including the system reset took about 2 hours. The actual ECU reset procedure was quick, roughly 15-20 minutes, but the workshop spent extra time verifying all control system functions were properly restored. The P0401 code (EGR flow) combined with P0103 (Mass Air Flow sensor high input) could indeed point to electrical supply issues, similar to what I experienced. The intermittent flashing and cold start problems match my symptoms before the relay replacement. After my repair, the workshop suggested monitoring the battery voltage as well, since unstable power supply can trigger ECU problems and similar error codes. In my case, the battery connections were also cleaned as a preventive measure during the repair. Since you mentioned the MAF sensor cleaning didnt help, checking the relay and its connection points is a logical next step before considering more extensive ECU repair options. The automotive electronics in these models are quite sensitive to voltage fluctuations through the main relay.

Thanks everyone for the insights about the relay issue. Just wanted to follow up and confirm the outcome of my Lupo repairs. The automotive electronics specialist found corroded terminals at the main relay, matching what was described. They cleaned all connection points, replaced the relay, and performed a system reset on the engine control unit. Total repair time was about 2.5 hours including full car diagnostics testing. The fix cost 145€ complete and resolved both error codes. Engine performance returned to normal and the control system is working perfectly now. Cold starts are smooth again with no check engine warnings. Really glad I checked about the relay first instead of jumping straight to an ECU replacement. The systematic diagnostic approach saved a lot of money and fixed the root cause. Will definitely keep monitoring battery voltage as suggested to prevent future issues. Thanks again for helping identify this common failure point in the electrical system. Hope this experience helps others with similar symptoms decide where to start their troubleshooting.