RS5 Cruise Control System Failure: What Goes Wrong

Had a similar issue with my 2020 RS4 a few months back. With some experience working on modern vehicle electronics, I can share what worked in my case. The cruise control system completely failed, showing similar symptoms, unresponsive steering wheel controls and error messages. After diagnostic testing, it turned out the problem was a damaged wiring connection between the steering wheel controls and the cruise control actuator. The fix was straightforward but required proper diagnostic equipment. My workshop found a loose plug connection in the steering wheel wiring harness that connects to the cruise control module. Total repair cost was 95 Euro, mainly for diagnostic work and fixing the connection. The throttle body can sometimes be involved in cruise control issues, but in this case, it was purely an electrical connection problem. These systems are quite complex with multiple potential failure points. Could you share: Any specific error codes from the scan? Does the issue occur constantly or intermittently? Are there any other electrical issues like warning lights? Have you noticed any changes in throttle response? This information would help determine if your issue matches what I experienced or if its something different in the faulty system.

Last service was at 88000 KM, and I have noticed some additional symptoms since my initial post. The malfunction seems to get worse when the engine is warm. I ran another diagnostic scan which showed error code P0638, suggesting its related to throttle actuator control. The steering wheel buttons are now completely dead, not just the cruise control functions. Going to book it in for repair next week, but wanted to see if anyone else encountered similar error codes with their RS5 before I commit to potentially expensive repairs.

Thanks for the additional details. When I had similar issues with my RS4, the error code P0638 also showed up later in the diagnostic process. The non-functional steering wheel controls combined with the throttle actuator error points strongly toward a more complex issue than my initial wiring problem. After seeing your symptoms, particularly the malfunction worsening with engine temperature, this sounds more like a faulty throttle body control module. In my case, after the initial repair attempt with the wiring, the problem returned and eventually required a complete throttle body replacement. The repair ended up costing 780 Euro, significantly more than the initial fix attempt. However, this resolved all issues: Cruise control functionality restored, Steering wheel controls working again, No more error messages, Smooth throttle response A key indicator was the warm engine correlation, this often suggests electronic component degradation rather than simple wiring issues. The throttle body malfunction can cause these cascading system failures because modern cruise control systems rely heavily on precise throttle control. Before your workshop visit, make sure they check the throttle body thoroughly, as replacing just the wiring might not solve the root cause if your symptoms match my later experience.

Based on your input about the P0638 error code and the steering wheel control issues getting worse with heat, I really appreciate the detailed sharing of your experience. My case definitely sounds similar to your throttle body replacement scenario. The car electronics are likely suffering from the same type of failure, especially given how the non-functional controls extend beyond just cruise control now. Will take your advice about the throttle body inspection, its good to know this could be more complex than a basic wiring fix. Already scheduled the repair for next week and I will make sure to mention the correlation with engine temperature to the technicians. The 780 Euro cost reference helps set realistic expectations for the repair budget. I will update this thread once I get the final diagnosis and repair completed. This information could help others who encounter similar cruise control system malfunctions with their RS models in the future. Thanks again for sharing your repair journey, its helped narrow down the likely causes before I head to the workshop.