Audi A4 ABS Warning Points to Speed Sensor Failure

I dealt with a very similar issue on my 2020 Audi A5 2.0 TFSI last year, and as someone with some experience working on cars, I initially thought it was just a sensor malfunction. The dashboard was showing the same ABS warning lights, and the traction control was behaving erratically. After some basic troubleshooting failed to resolve the issue, I took it to a workshop where they diagnosed a defective ABS control unit. The complete repair, including parts and labor, came to 1000 Euro. The issue turned out to be more complex than just a faulty input sensor or wiring problem. The control unit itself was malfunctioning, causing both the ABS and traction control systems to behave unpredictably. The odometer and speedometer were working fine, which initially made diagnosis tricky. Before offering more specific advice, could you share: Have you noticed any other warning lights? Does the problem occur more frequently at certain speeds? Have you recently had any other work done on the braking system? Did the issue start suddenly or develop gradually? This information would help determine if your situation matches what I experienced or if its something different.

Last service was at 191000 KM, and my odometer currently shows 195680 KM. The ABS warning remained on even after clearing the fault codes with my OBD reader. The speedometer works as expected, but when I engage the brakes firmly, I can feel the ABS isnt functioning properly. Started suddenly during a rainy week. No other warning lights on the dashboard except for the ABS indicator. No recent brake work done, and it happens consistently at any speed. Just scheduled a diagnostic appointment since these symptoms seem to match what you experienced with the control unit issue.

Based on the mileage and symptoms you described, it definitely mirrors my experience with the control unit failure. When my ABS malfunction occurred, the diagnostic scan initially pointed to a speed sensor, but the consistent ABS warning despite clearing codes was the key indicator of a deeper issue. The fact your speedometer works normally while the ABS behaves inconsistently during braking matches exactly what happened with my A5. The rainy conditions likely made the symptoms more noticeable due to increased ABS activation needs. My repair process went like this: Initial diagnostic scan, Control unit testing, Full ABS system inspection, Control unit replacement, System recalibration Total repair time was about 4 hours. While 1000 Euro might seem steep, the control unit is a complex component that manages both ABS and traction systems. Getting it fixed promptly is crucial since compromised ABS function increases stopping distances significantly. The workshop found slight corrosion on my control unit connectors, likely from moisture exposure. Since your issues started during wet weather, they should check for similar damage during the diagnostic appointment. Watch for any new dashboard warnings before your appointment, as they could help pinpoint if other systems are being affected.

Thanks for the detailed explanation. Your experience definitely puts my mind at ease about the upcoming diagnostic appointment. I was initially hoping it was just a simple sensor input issue, since replacing the ABS control unit is quite expensive. Given how similar our symptoms are, the constant ABS warning light, the speedometer working fine but ABS not engaging properly, and the traction issues, I suspect youre right about the control unit being the culprit. Will have the workshop check the connectors for moisture damage too, considering the timing with the rainy weather. Really appreciate the breakdown of the repair process and costs, helps me know what to expect. At least now I can go into the appointment better informed about the likely cause and potential repair costs.