Audi SQ8 ABS Failure Points to Speed Sensor Issues

I dealt with nearly identical symptoms on my 2021 Q7 TDI. With some experience working on Audis, I recognized these as classic signs of a malfunctioning ECM affecting multiple vehicle systems. The speedometer fluctuations combined with ABS and traction control issues initially pointed to speed sensors, but diagnostic testing revealed a defective control unit. The workshop found that the ECM was misinterpreting input signals from various sensors, causing the transmission and safety systems to malfunction. The fix required replacing and programming a new control unit, which resolved all symptoms. Total cost was around 1000 Euro including parts, labor and programming. Since the repair, all systems have functioned perfectly with no recurring issues. To provide more specific advice for your case, could you share: Current mileage, Any recent repairs or modifications, Whether the issues started suddenly or developed gradually, Any diagnostic codes you may have retrieved, If the problems occur more frequently under specific conditions These details would help determine if your SQ8 is experiencing the same underlying issue as my Q7.

Just had my car serviced at 82155 KM and have run all preliminary diagnostics. The odometer sensor signals seem normal when tested individually, suggesting the malfunction might be in how the ECM processes these inputs rather than the sensors themselves. My service records show no previous issues with the ABS system until these symptoms appeared suddenly last week. The error codes point toward a communication issue between components rather than individual sensor failures. Has anyone else tracked down similar symptoms to a specific control unit?

Having gone through this exact situation with my Q7, I can confirm this aligns perfectly with what I experienced. The error codes indicating communication issues rather than sensor failures match my case precisely, where the ECM was misinterpreting otherwise healthy sensor inputs. The sudden onset of symptoms, particularly affecting multiple systems simultaneously (ABS, speedometer, traction control), strongly supports my initial diagnosis of a control unit problem. The fact that your individual sensor tests show normal readings further validates this conclusion, as this mirrors the diagnostic path in my case. A key observation from my experience: the transmission control module also began showing intermittent communication errors shortly after the initial symptoms appeared. If you're seeing similar patterns, it would further confirm the ECM as the root cause. The resolution in my case (ECM replacement and programming) completely eliminated these issues. Given the matching symptom pattern and diagnostic results, I would strongly suggest pursuing the same repair path that worked for my vehicle, especially since you've already verified the sensor functionality. Running costs might vary, but my 1000 Euro repair proved to be a complete fix, with no recurring ABS or traction control issues since.

Thanks for sharing those diagnostics! The communication issue theory makes a lot of sense based on how the dashboard indicators are behaving. My transmission specialist checked further and found that the control unit was indeed misinterpreting signals despite the sensors testing fine individually. The timing of the malfunction appearing suddenly right after routine service is interesting, makes me wonder if something got disturbed during maintenance. I'll definitely have them focus on the ECM/control unit angle rather than replacing individual sensors. The error codes pointing to communication problems rather than sensor failures seems to be a crucial diagnostic clue that others have confirmed led them to successful repairs. Really appreciate everyone sharing their similar experiences, helps narrow down the likely culprit before heading to the shop. Will update once I get it properly diagnosed and repaired. At this point, I'm expecting it may need a new control unit based on how closely these symptoms match what others described. The sensor data all checking out normal individually definitely supports that theory.