ABS & Traction Control Failure Points to Speed Sensor

Having some experience with these systems, I encountered a very similar issue with my 2009 Audi S5. The malfunction showed almost identical symptoms, with dashboard warning lights and sensor problems. After multiple diagnostic attempts, my workshop found that the ABS control unit itself was defective, not just the wheel speed sensors. The speedometer worked fine, but the entire ABS system was compromised. The odometer and other basic functions remained operational, but the safety systems were completely disabled. The repair involved replacing the complete ABS control unit, which cost around 1000 Euro including programming and calibration. The workshop had to use specialized diagnostic equipment to properly integrate the new unit with the vehicle systems. To better assist with your specific case, could you share: Have you noticed any unusual noises when braking? Did the issue appear suddenly or develop gradually? Are there any other warning lights active on your dashboard? Has the vehicle been involved in any recent accidents or flood damage? Have you had any recent brake work done? This information would help determine if your issue matches what I experienced or if it might be something different.

Thanks for the information. I have 124176 KM on my car and the last service was done 3 months ago. The braking system actually makes a grinding noise when applying moderate pressure. The diagnostic scan shows error code P0500 which points to a speed sensor signal malfunction in the transmission system. The ECM appears to receive inconsistent input from the speed sensors. The noise developed gradually over the past month, starting as a slight click and progressing to the current grinding sound. There are no other warning lights active besides the ABS and traction indicators. The car has not been in any accidents or exposed to water damage. No recent brake work has been performed aside from regular pad changes during the last service. Would appreciate any additional insight based on these symptoms, particularly regarding the grinding noise combined with the sensor malfunction.

Based on your description and comparing it to my experience with the same model, I believe we are dealing with different root causes. While my issue was purely electronic, your grinding noise combined with the transmission sensor malfunction points to a potentially more complex problem. The speedometer working despite the error code P0500 suggests the main transmission sensor might be functioning, but the ABS wheel speed sensors could be compromised by mechanical wear. The grinding noise during braking is particularly concerning and wasnt present in my case. In your situation, I would recommend: 1. Inspect the wheel bearings, as failing bearings can damage the integrated speed sensors 2. Check the tone rings on each wheel for damage or debris accumulation 3. Test the wiring harness between the sensors and ABS module for any breaks The progressive nature of your symptoms, especially the evolving grinding noise, suggests mechanical wear rather than the sudden electronic failure I experienced with my ABS control unit. My repair cost of 1000 Euro for the control unit might not be relevant here, as you may be looking at both sensor replacement and mechanical repairs to address the grinding. The malfunction appears to stem from physical wear rather than pure electronic failure. Would suggest having the wheel bearings checked first, as this could explain both the grinding and sensor issues in one go.

Thanks for all the feedback. After getting this detailed information, I went ahead and had my wheel bearings inspected. Turns out there was significant wear on the front driver side bearing, which was causing both the grinding noise and affecting the ABS sensor readings. The mechanic found metal debris had accumulated around the tone ring, interfering with the sensor signal to the ECM. This explains why the diagnostic showed the P0500 code and why the ABS system was malfunctioning. The transmission speed sensor itself was actually fine. Total repair came to 450 Euro including a new wheel bearing assembly, speed sensor replacement, and labor. The grinding noise is now completely gone and all warning lights have cleared. The ABS and traction control systems are working perfectly again. This was definitely different from your ABS control unit issue, though the initial symptoms seemed similar. Really appreciate everyone helping track down the actual problem. Would recommend anyone with similar symptoms check their wheel bearings first before assuming its purely an electronic or sensor issue.