Audi A7 Stuck Fault Codes: Expert Fix Guide

Had a similar fault code issue with my 2020 A6. The control unit kept showing locked error codes that wouldnt clear no matter what diagnostic tool was used. After checking several auto repair forums, I suspected an undervoltage problem in the computer system. Took it to a workshop where they confirmed the voltage issue was preventing the fault codes from being cleared properly. The root cause was a failing voltage regulator affecting the car electronics. Total repair came to 240 Euro and took about 3 hours to complete. What engine type does your A7 have? Also, are you getting any specific error messages along with the locked codes? This would help determine if youre dealing with the same underlying issue. Some key questions that could help diagnose this: Are there any warning lights on the dashboard? Have you noticed any electrical issues like dimming lights? Does the issue persist after a full battery charge? Which diagnostic tool are you using to read the fault codes?

Latest service was at 120000 KM, just 2200 KM ago. Like others suggested, I also first checked the battery voltage. All electrical systems appear normal, no flickering lights or warnings on the dash. Using a professional diagnostic tool from a certified workshop. The active memory shows fault code P0420 that remains locked in the control unit despite multiple reset attempts. The car electronics seem otherwise fine, but the computer system keeps these codes active. Already tried disconnecting the battery for 30 minutes with no success. The engine operates smoothly with no performance issues, which makes this persistent fault code even more puzzling. Currently waiting for feedback from the auto repair center about a potential software update for the ECU.

Interesting update about your A7. On my A6, I initially had similar symptoms with a locked P0420 code in the control unit. While the voltage regulator was one issue, I later discovered that error persistence can also stem from the catalytic converter monitoring system, even when the engine runs fine. The automotive diagnostics showed the code was stuck because the ECU kept detecting catalyst efficiency below threshold, though no obvious performance issues were present. A software update to the control unit helped in my case, but I also needed the O2 sensors replaced as they were providing incorrect readings to the computer system. Since youve already checked voltage and battery, and given your recent service history, Id suggest having the workshop specifically check: O2 sensor functionality, Catalyst monitoring thresholds in the ECU fault parameters, Latest software version for the engine control module The active memory might be retaining these fault codes due to sensor values falling just outside acceptable ranges. The total fix for my A6 cost around 460 Euro including the software update and sensor replacement. Let us know what the workshop finds regarding the software update. These persistent fault codes often need dealer-level diagnostic equipment to fully resolve.

Thanks for sharing those detailed experiences. After getting your responses and comparing them with my situation, I decided to have the workshop perform a complete ECU diagnostics review. The auto repair center confirmed my suspicions about the O2 sensors. They found the downstream sensor was providing inconsistent readings to the computer system, causing the P0420 code to remain locked in active memory. The memory lock persisted because the ECU kept receiving conflicting data. They performed a software update and replaced both O2 sensors. Total repair cost came to 520 Euro including diagnostic time and parts. The fault codes finally cleared from the control unit and haven't returned after 300 KM of driving. Really appreciate the guidance about checking the catalyst monitoring thresholds, this helped the technicians pinpoint the exact issue faster. Will update this thread if anything changes, but for now, the car electronics are working perfectly and all diagnostic systems show normal operation.