VW Taos ECU Lock Creates Multiple Fault Code Puzzle

Had a similar issue with my 2021 VW T-Cross. Having some experience with car electronics and fault codes, I first tried clearing the active memory myself using a diagnostic tool, but no success. The root cause in my case was undervoltage in the vehicle electrical system, which triggered multiple control unit errors. The workshop found the battery voltage had dropped below critical levels, causing the ECU to enter a protective state and lock the fault memory. The diagnostic steps included: Complete system voltage check, Battery load test, Alternator output verification, Control unit communication test Total repair cost was 240€, which covered: Battery replacement, System diagnostic, Fault code clearing, Control unit reset To better assist with your case, could you share: Battery age and last replacement date, Whether you noticed any starting issues, If any electrical accessories were recently installed, What specific fault codes are showing up These details would help determine if your issue stems from the same underlying problem. While the engine running fine is positive, persistent fault codes often indicate a power supply problem that needs addressing before it affects other systems.

Last service at 131159km shows everything was fine, but this new issue is concerning. After running the diagnostic steps you suggested, my scanner shows eight different fault codes in the active memory, all related to communication errors between control units. Unlike your case though, my battery tests normal and the alternator output is within specs. The computer system seems stuck in this error state despite having proper voltage. The automotive diagnostics also indicate normal communication on the CAN bus, which makes the fault memory lock even more puzzling. Wonder if this could be related to the latest ECU software update that was done during my last service visit.

Thanks for those additional details about your VW Taos. My T-Cross actually showed similar symptoms after a software update, though initially I thought it was just the battery like in my first case. The ECU fault codes being stuck after an update is a known quirk in our vehicle computer system. The main difference from my previous battery-related issue was exactly what you described, all power systems testing normal but the fault memory remaining locked. The auto repair shop found that the software update had not completed properly, leaving the ECU in a partial update state. This explains why the computer system shows those communication errors between control units while everything else functions normally. The fix required: Complete ECU diagnostics scan, Force-clearing the update state, Reflashing the control unit software, Resetting adaptations Final cost was 320€ including the complete ECU diagnostics and software reflash. Much different from my previous battery-related repair, but solved the persistent fault codes completely. Looking at your case, the timing with the recent service update strongly suggests the same root cause. Recommend having the control unit software reinstalled rather than just attempting to clear the codes.

Thanks for sharing the experience with your T-Cross issue. What you described about the software update matches my situation perfectly. Just scheduled an appointment to have the ECU diagnostics and reflash done. In case it helps others, my fault codes specifically show communication timeouts between modules, exactly like what happened in your case. The fact that all power systems are testing normal but the fault memory lock persists definitely points to an incomplete software update rather than a hardware problem. Will update once the repair is done, but based on the similarities with your experience, the control unit reflash should resolve these stubborn fault codes. The quoted cost is also in line with what you paid, they estimated 350€ for the complete ECU diagnostics and software reinstallation. The weird part is how the car electronics keep functioning normally despite these communication errors showing up in the computer system. At least knowing this is likely just a software glitch rather than a serious mechanical issue gives me some peace of mind.