Q3 ECU Fault Memory Lock Needs Expert Diagnosis

Faced a similar control unit issue on my 2019 Q5 last year. The ECU diagnostics showed multiple undervoltage codes in the active memory, which initially seemed like a simple battery problem. The computer system was registering fault codes across multiple modules, creating a fault memory lock, exactly like your situation. This typically happens when voltage drops below critical levels, causing the control units to protect themselves. The root cause turned out to be more complex than just a weak battery. The auto repair technician found corroded battery terminals and a failing voltage regulator in the alternator. These components were causing intermittent power supply issues to the ECU. The repair required: Complete alternator replacement, Battery terminal cleaning and replacement, ECU reset after repairs This was indeed a serious issue that needed immediate attention, as continuing to drive with undervoltage problems can damage multiple electronic components over time. The fault memory lock is actually a protective measure by the vehicle computer system. Would strongly recommend getting this checked, as these symptoms match a known pattern of power supply issues in that model range.

Thanks for sharing your experience with the ECU fault issue. Your case sounds very similar to what happened with my Audi Q3 last spring. After multiple fault codes kept appearing, it turned out the control unit was getting incorrect voltage readings due to a faulty wiring harness, not the alternator they initially suspected. The fault memory lock was indeed a protective response from the car electronics, but I am curious, do you remember roughly how much you ended up paying for the full repair? Also, have you experienced any related electrical issues since the fix was completed?

Good news on your control unit concerns. I ended up paying 240 Euro for the complete fix at the auto repair shop, which was less than expected considering the initial diagnosis suggested more extensive repairs might be needed. The automotive diagnostics confirmed it was strictly an undervoltage issue. The fault memory lock was successfully cleared after the repair, and I can confirm the computer system has been working flawlessly since then. The ECU diagnostics now show no recurring faults or voltage-related issues. Unlike your situation with the wiring harness, my problem was resolved by addressing the power supply components directly. To answer your question about subsequent issues, the car has been running perfectly for the past 8 months with no electrical problems whatsoever. The investment in proper ECU fault diagnosis and repair proved worthwhile, as it prevented potential damage to other electronic components that could have failed due to voltage irregularities.

Thanks everyone for the insights. After dealing with the fault codes issue, I finally got my Q3 fixed last week. The mechanic found the computer system was indeed showing those codes due to a damaged wiring harness, causing the ECU diagnostics to misread voltage levels. The repair took about 4 hours and cost 380 Euro, including parts and labor. They had to replace a section of the wiring harness and clear all the active memory fault codes. The car electronics are now working perfectly, no more warning lights or fault memory lock issues. What surprised me was discovering the wiring damage was actually caused by a small leak in the firewall grommet that had allowed moisture to corrode the connections over time. A simple rubber seal could have prevented the whole problem. Really glad I asked for opinions here before letting the first shop replace the alternator unnecessarily. The correct diagnosis saved me both time and money.