Audi Q8 Cruise Control Dead, Speed Sensor Suspected

Had a similar issue with my 2017 Audi Q7 last year. Have some experience working on Audis and this exact problem came up during highway driving. The cruise control suddenly failed and fault codes appeared. Initially thought it was the speed sensor or throttle position sensor, but after inspection at my trusted workshop, they found a loose cable connection near the pedal switch assembly. The wiring had worked itself loose over time, causing intermittent connection issues. Total repair cost was 95 Euro, mostly labor for accessing and fixing the connection. Much cheaper than replacing entire components. The fix took about an hour and cruise control has worked flawlessly since. What engine variant does your Q8 have? Also, when exactly did the issue start, was it gradual or sudden? This info would help determine if youre dealing with the same issue. Its worth checking the fuse box first, there are specific fuses for the cruise control system that could be blown. Since these systems are quite complex on modern Audis, might want to have a professional diagnose it properly. Could save money in the long run rather than replacing parts unnecessarily.

Thanks for sharing your experience. Just had my service done at 190746 KM and everything else is running fine, just this cruise control issue came up right after. A quick check of the fuse box showed all fuses are intact. The dashboard light for cruise control comes on normally when starting the car but goes off immediately when trying to activate it. Looking at the fault codes again, they seem to point toward the clock spring, though visually everything looks fine with the steering wheel controls. Hoping its just a connection issue like yours rather than a complete unit replacement. Will get it properly diagnosed rather than guessing.

Thanks for the update. Since you mentioned it started right after the service, this reminds me exactly of what happened with my Q7, the timing is suspiciously similar. The symptoms you describe with the dashboard light behavior match what I experienced. While my issue ended up being the loose connection at the pedal switch, the clock spring was actually our first suspect since the steering wheel controls seemed to respond inconsistently. One quick test you can try: check if your horn works properly and if the steering wheel buttons feel different when pressed at various steering angles. This can help indicate if the clock spring is actually the culprit. In my case, these all worked fine, which led us to look elsewhere in the system. The cruise control system has multiple fail-safes, and any break in the circuit, whether at the pedal switch, clock spring, or elsewhere, will cause it to deactivate immediately. Since your fuses are good, Id bet on either a connection issue or the clock spring. Based on my experience with the repair costs, a connection fix would be around 100 Euro, while a full clock spring replacement could run 400-600 Euro depending on the specific part needed.

Thanks for all the feedback. I went ahead and did the steering wheel check you suggested, the horn and other buttons work perfectly at all angles, so that's somewhat reassuring. Makes me think the clock spring might not be the issue after all. Called my shop and booked it in for next week. They mentioned theyve seen similar cases where the throttle position sensor or brake light switch connections get disturbed during routine maintenance. The dashboard light behavior matches what you described too. Will let the techs know about the connection issue possibility, especially since it started right after the service. Hoping its just a loose wire near the pedal switch like in your case, that 95 Euro repair bill sounds much better than replacing major components. Thanks again for helping narrow down the possibilities. At least I can go to the shop better informed about what they should be checking first.