VW Up Cranks But Won't Start, ECU Failure Suspected

Had the same problem with my Polo TSI last year. The check engine light came on and the engine would crank but not start. After running engine diagnostics, it turned out the battery cable connections were heavily corroded, creating poor contact. The corrosion prevented proper voltage from reaching the ECU, which caused the engine surge symptoms and starting issues. When battery connections are compromised, the ECU can receive inconsistent power, making it seem like an ECU failure. The fix involved cleaning the battery terminals and cable ends, replacing the corroded connectors, and applying anti-corrosion coating. Not a serious repair but critical for proper engine function. The engine fault codes cleared after fixing the connections. Worth checking the battery connections first before assuming ECU problems. Poor connections often trigger similar symptoms but are much simpler to fix. Had no starting issues since the repair was done at 98000km.

Thanks for sharing your experience with the battery connections. Definitely sounds similar to what Im dealing with. Really hoping its just corrosion like in your case and not a full ECU replacement. The engine stalling symptoms match exactly what Im seeing. Did you remember roughly how much the repair cost? Also curious if you had any fuel injection issues or other electrical problems show up after fixing the battery connections? Currently weighing my options between two repair shops, so trying to get an idea of the potential costs involved if its the same root cause.

Just got the car back last week after fixing those exact same issues you described. The engine control malfunction warning disappeared right after they cleaned and replaced the corroded battery connections. Total repair came to 155€, which included new connectors and the anti-corrosion treatment. Since the fix, no engine stalling or electrical problems at all. The engine starts perfectly every time and the check engine light has stayed off. The fuel injection system works normally too, no issues there. Looking back, the engine diagnostics clearly showed it was just the bad connections causing all those ECU-like symptoms. Much cheaper than replacing the entire unit. My Polo runs like new now, and the mechanic said these connection problems are actually pretty common on these models.

Found a reliable garage through an online forum and took the car in yesterday. The mechanic immediately spotted heavy corrosion on the battery terminals, just like you described. They cleaned everything, replaced the connectors, and applied some protective coating. Cost me 180€ total. The check engine light turned off as soon as they fixed the connections. No more engine stalling or starting problems. Such a relief it wasnt an actual ECU failure. The engine diagnostics also came back clear after the repair. Figured Id update the thread in case someone else runs into similar issues. Sometimes the simplest explanation is the right one. Really glad I checked here before assuming the worst about the ECU. Would have spent way more money unnecessarily. The car starts perfectly now and all electrical systems are working normally. Happy to report zero engine surge problems since the fix. Thanks again for pointing me in the right direction with the battery connection issue.