VW Transporter ABS Fault Linked to Speed Sensor Issues

Had nearly identical issues on my 2021 VW Multivan last winter, as someone with moderate experience working on VWs. The diagnostic codes from the ECM pointed to a faulty speed sensor initially, but after professional testing, it turned out the ABS control unit itself was defective. The speedometer and odometer were working fine, but the ABS system remained completely disabled. Took it to a specialized workshop where they confirmed the control unit failure through comprehensive testing. The repair involved: 1. Complete diagnostic scan 2. Removal and replacement of the ABS control unit 3. Programming and calibration of the new unit 4. Final systems check Total cost was 1000€ including parts and labor. Since the repair, all systems have worked flawlessly. Before you head to a shop, could you share: Exact error codes from the diagnostic scan, Whether your speedometer is working normally, If you notice any unusual sounds when braking, When the issue first appeared This information would help determine if you are dealing with the same underlying problem or if it might be something simpler like a sensor issue.

Last service was at 120000km, currently showing 121501km. The error codes from my scan tool show P0500 (Vehicle Speed Sensor A) and C1241 (ABS Sensor Circuit). The speedometer works intermittently, sometimes showing correct speed, other times dropping to zero while driving. No unusual sounds during braking. The malfunction first appeared after driving through heavy rain last week. The transmission still shifts normally, but the ECM seems to be getting incorrect speed signals. Could be a wiring issue since water exposure triggered the problem. Will try cleaning the sensor connections before pursuing more expensive repairs.

Thanks for those additional details. Unlike my case where the ABS control unit was the culprit, your symptoms strongly point to a speed sensor or wiring issue, especially given the speedometer behavior and the timing with the rain exposure. The intermittent speedometer readings and transmission continuing to shift normally are key differences from what I experienced. In my case, the speedometer remained consistently functional despite the ABS and traction failures. Based on the P0500 code and the rain correlation, I recommend: 1. Locate the speed sensor on the transmission housing 2. Disconnect and inspect the wiring harness for corrosion 3. Clean all sensor connections with electrical contact cleaner 4. Check for any obvious signs of water damage or loose connections 5. Test the sensor resistance with a multimeter if possible This approach should cost under 20€ in cleaning supplies versus the 1000€ I spent on the control unit replacement. If cleaning and inspection dont resolve the dashboard warnings, then professional diagnosis would be the next step. The input from your speed sensor affecting multiple systems (ABS, speedometer, traction) suggests this is likely a simpler fix than what I encountered.

Thanks for the detailed suggestions. Just checked the speed sensor connections and found significant corrosion on the wiring harness near the transmission housing. The electrical contact cleaner helped, my speedometer is now working consistently and the ECM is getting proper speed signals. However, the ABS warning light remains on. Going to pick up a multimeter tomorrow to test the sensor resistance as suggested. The fact that multiple systems were affected by this malfunction does make me optimistic its just a connection issue rather than a full control unit failure. If the resistance test shows problems, at least I know to focus on the sensor itself rather than jumping straight to replacing the more expensive ABS components. Much better starting point than the 1000€ repair you went through. Will update once I complete the sensor testing.