VW A2: ECU Fault Lock Won't Clear Despite Good Engine

Had the same fault memory lock issue with my 2005 A3 1.6L. The ECU diagnostics initially showed an undervoltage error that would not clear despite multiple reset attempts. The root cause turned out to be deteriorating wiring harness connections to the ECU, creating intermittent voltage drops. Though the engine ran fine, these voltage fluctuations triggered the permanent fault code storage in the control module. The fix required a thorough automotive diagnostics session to trace the exact location of the voltage drop. The technician found corroded pins in the main ECU connector and damaged insulation on several wires. Simply clearing fault codes would not have solved this, as the underlying electrical issue kept triggering new entries in the fault memory. The repair involved cleaning connector pins, replacing damaged sections of the wiring harness, and properly sealing all connections. After addressing the wiring issues, the fault codes could finally be cleared permanently. This was a serious electrical system concern that needed professional attention, as deteriorating connections can eventually lead to ECU failure or erratic engine behavior. Would recommend having a specialist with proper diagnostic equipment examine the entire ECU wiring system.

Thanks for the detailed write-up about the ECU wiring issue. The fault codes in my computer system kept coming back until I got it properly diagnosed too. My mechanic found similar problems with corroded connections affecting the memory lock function. How much did the complete repair cost you? And have you experienced any other electrical gremlins since getting it fixed? Just want to make sure the fix is holding up well before I commit to a potentially expensive repair on my A2.

Yes, you can rest assured, it has been over 6 months since getting the repair done and the fault memory lock active issue has not returned. The automotive diagnostics revealed it was definitely the undervoltage problem causing the persistent ECU errors, just as suspected. The complete repair including parts and labor came to 240 Euro, which was reasonable considering the thorough electrical system inspection and repair work needed. The control unit now operates perfectly with no recurring fault codes or active memory issues. The ECU diagnostics also confirmed that addressing those corroded connections was crucial, leaving them unfixed could have led to more serious car electronics problems down the line. Have not experienced any electrical issues since the repair. The investment in proper diagnosis and repair was worth it for the long-term reliability of the vehicle's electrical system. Looking back, trying to clear the codes without fixing the underlying voltage issue would have been futile. A proper automotive diagnostics session was key to identifying and resolving the root cause.

Thanks for the input. After reading about similar experiences, I finally got my car properly diagnosed and fixed. The mechanic found corroded wiring and poor connections causing the persistent ECU fault. The repair cost me 290 Euro total. The technician spent about 3 hours doing a complete diagnostics check of the control unit and electrical system. They cleaned all connections, replaced some damaged wiring, and properly sealed everything. The fault memory finally cleared and has stayed clear for the past month. Most importantly, they explained why previous attempts to clear the active memory failed, the constant voltage fluctuations from bad connections kept triggering new fault codes. Really glad I got it properly sorted instead of just trying quick fixes. For anyone else facing similar issues, definitely worth getting a proper diagnostic scan done by someone who knows these electrical systems well. Trying to clear fault codes without fixing the underlying problem is just wasting time and money.