E-tron Control Module Issues Plague Multiple Systems

As someone with some experience working on EVs, I had a very similar issue with my 2019 e-tron 55 quattro last year. The symptoms were nearly identical, unusual system failures, warning lights appearing intermittently, and various control modules becoming unresponsive. After running engine diagnostics, my workshop found that the main control unit had a faulty cable connection to the vehicle BUS system. The malfunction indicator would come on out of nowhere because the modules were losing communication with each other. The OBD-II scan showed multiple error codes that didnt make much sense initially, which is typical for BUS communication issues. The repair involved replacing the wiring harness connector and testing all the connections to ensure proper communication between modules. Total cost was 155 Euro including diagnostics and parts. Before suggesting specific solutions, could you share: Have you noticed any pattern when these failures occur? (cold starts, after driving for a while, etc.), Which specific warning lights are appearing? Has your dealer performed a full system diagnostic scan? Are there any visible signs of water damage or corrosion around the main control unit? This could help determine if youre dealing with the same root cause or if theres another issue at play.

Had my last service at 115000km where they ran a full check engine diagnostic scan. The warning lights and module failures started occurring about 3000km after that service. The dealer found multiple temporary fault codes but couldnt replicate the issue during their initial inspection. The issues seem most frequent during cold starts and the warning signals consistently show electrical system faults. The check engine light flashes intermittently along with stability control warnings. Interesting to hear about the BUS system connection, will have them specifically look at the wiring harness next week when I bring it back in. Noticed the malfunction indicator comes on more frequently when using climate control, if that helps narrow things down.

Thanks for the additional details about the timing of issues and warning patterns. When I had similar symptoms with my e-tron, the connection problems also showed up more frequently during cold starts and climate control usage. This lines up perfectly with what I experienced before discovering the faulty BUS connection. The service required in my case became obvious after the scan tool revealed multiple communication errors between the climate control module and the main control unit. The system failure patterns you describe strongly suggest a similar wiring harness issue, especially given the correlation with climate control usage. A few observations from my repair experience: The temporary fault codes are typical when dealing with intermittent connection issues, The combination of electrical system faults and stability control warnings matches the symptoms of a compromised BUS system, Climate control triggering the malfunction indicator often points to communication problems rather than component failures Make sure your dealer performs a thorough check of all wiring harness connections, particularly around the climate control module. In my repair, they initially missed the issue by only checking individual components rather than the connections between systems. Would recommend having them document all error codes during both cold and warm conditions while running the climate control. This helped identify the root cause in my case.

Thanks for the input. Just got back from the dealer and wanted to update on what they found. After reading about the BUS system issues mentioned here, I specifically asked them to check the wiring harness connections. The scan tool confirmed multiple communication errors between modules, exactly matching what was described. They found corroded terminals in the main wiring harness connector that connects to the climate control module. The warning lights and system failures were happening because of poor connections causing intermittent communication loss. Total repair cost was 380 Euro including labor and parts to replace the affected wiring harness section and clean all connecting terminals. They also applied dielectric grease to prevent future corrosion. All systems are now working properly. No more unusual warning lights or module failures during cold starts. The malfunction indicator hasn't come on once since the repair, even with heavy climate control usage. For anyone else experiencing similar issues, definitely have them check the wiring harness connections first before replacing more expensive components.