Audi S5's Critical Electrical System Chaos Needs Fix

Had a similar issue on my 2020 Audi S4. The symptoms started exactly the same way, unusual system failures and warning signals appearing without any clear pattern. The check engine light was particularly frustrating as it would turn on and off out of nowhere. After running engine diagnostics through OBD-II, the root cause was traced to a damaged connection in the main control unit BUS system. The constant vibration had worn down the cable insulation, causing intermittent connection issues throughout the electrical system. The service required was more extensive than initially thought since multiple systems were affected. The core problem was that when the BUS connection fails, it disrupts communication between various control modules. This explains why you are seeing multiple systems affected, from infotainment to engine management. This is definitely a serious issue that needs proper diagnosis and repair. A complete scan of all control modules is necessary, not just basic troubleshooting. The unusual nature of these failures is typical of BUS communication problems, and attempting partial fixes often leads to recurring issues. Based on your description, it sounds identical to what I experienced. Would strongly suggest having a full system diagnostic done by a shop with Audi-specific diagnostic equipment.

Thanks for sharing that detailed info about the BUS system issue. This matches what my S5 was doing before I got it fixed. The malfunction indicator was driving me crazy with its unusual appearances. Good to know Im not alone with these electrical gremlins. I ended up getting my control unit replaced but curious how much your repair ended up costing? Mine was pretty steep but wondering if I paid too much. Also, has your system been stable since the fix or have you noticed any other quirks pop up? My scan tool still occasionally shows some minor communication errors but nothing like before.

Good to hear the fault message issues have settled down on your S5. After my repair, which ended up being 155 Euro to fix the faulty cable connection in the control module, my system has been running perfectly stable. The previous unusual warning signals and system failures completely disappeared. The BUS system communication is now working as intended, and the malfunction indicator hasnt shown up since. It turned out to be a relatively straightforward fix once the technician properly diagnosed the root cause. The repair cost was actually quite reasonable considering the complexity of modern vehicle electrical systems. From what you mentioned about still seeing occasional communication errors on your scan tool, it might be worth having those checked just to be safe. Sometimes these minor OBD-II readings can indicate early signs of developing issues. But if youre not experiencing any actual system failures like before, it could just be normal electronic noise.

Thanks for the input. After reading about the BUS system issues, I finally took my S5 to a certified shop that specializes in German cars. The warning lights were indeed related to a failing control module, just as suspected. The repair wasnt cheap, 890 Euro for parts and labor, but the car runs perfectly now. No more unusual system failures or warning signals popping up on the dash. The scan tool readings are all clean too. The mechanic showed me the damaged wiring harness that was causing all the communication issues between modules. Funny thing is, when they hooked up their diagnostic system, they found over 50 stored error codes from all the intermittent failures. The technician said it was one of the worst cases of electrical gremlins he had seen in a while. Really glad to have this sorted out finally. Should have gone to a proper shop from the start instead of wasting time with that first mechanic who clearly had no idea what he was doing. Just wanted to close the loop on this one and say thanks for pointing me in the right direction with the BUS system diagnosis.