Q5 Electrical Chaos: Multiple Module Failures

When my 2011 Audi A5 showed similar symptoms, it turned out to be a faulty cable connection to the main control unit affecting the BUS system. The malfunction indicator would illuminate out of nowhere, and multiple systems would fail intermittently, just like your case. The scan tool showed various error codes across different modules, making engine diagnostics initially confusing. The service required message kept appearing even after clearing the codes. After thorough testing, the root cause was traced to corroded wiring connections at the main control module. The repair involved replacing the entire wiring harness connecting to the control unit and recalibrating the system. This was a serious issue that required specialized diagnostic equipment and expertise. While not immediately dangerous to drive, leaving it unfixed could lead to complete system failure and potential safety concerns. The check engine light issues stopped completely after the repair, and all electrical systems returned to normal operation. This is a known weakness point in some Audi models from that generation, and proper diagnosis is crucial to avoid replacing unnecessary parts. Consider finding a shop specializing in Audi electrical systems, as general repair shops often struggle with complex BUS system issues.

Thanks for sharing your experience with the A5 electrical issues. The symptoms you described sound exactly like what Im dealing with in my Q5. Since our cars are from around the same generation it makes sense they might share similar issues. Its really helpful to know about the wiring harness being the culprit. When I take it to the shop Ill make sure to mention checking the connections at the main control module first. A complete system failure is definitely something I want to avoid. Would you mind sharing how much the repair ended up costing? Also curious if youve had any recurring electrical problems since getting it fixed? Hoping a proper diagnosis will help avoid unnecessary part replacements and get this sorted once and for all.

Thanks for checking back. I'm glad to report the warning signal issue was completely resolved after visiting the mechanic. The total repair cost came to 155 Euro for fixing the defective cable connection at the control unit where it connects to the BUS system. Since the repair, all systems have been working perfectly, no more unusual malfunction indicator lights or system failures. The OBD-II scan shows zero error codes now, and the electrical systems are all functioning as they should. This repair proved to be significantly more cost-effective than initially feared, especially considering the potential for more extensive damage if left unfixed. The communication problems between modules have completely disappeared, confirming it was indeed just the faulty connection causing all those unusual issues. The key was finding a technician who understood these complex electrical problems rather than just replacing parts hoping to fix the issue. The investment was definitely worth it for the peace of mind alone.

Thanks everyone for your input. I finally got my Q5 fixed last week. After reading about similar experiences here, I specifically asked them to check the control module connections and wiring harness. Turns out there was significant corrosion at the main connection points, causing all those unusual warning lights and system failures. The mechanic cleaned and repaired the connections, then performed a full system reset. Total repair cost was 180 Euro, which was much better than I expected. All the electrical gremlins are gone now. No more malfunction indicators, the navigation works perfectly, and all control modules are responsive. The engine diagnostics show everything is running normally. Really glad I got this sorted before any major system failure occurred. Good to know these electrical issues are somewhat common in Audis from this era. Having the right information definitely helped me avoid unnecessary parts replacement and direct the mechanic to the actual problem.