The brief
The Sharan came in with a warning light on, and a diagnostic check tracked it down. The culprit was a wheel speed sensor, the kind of fault that's easy to misread from the dash and needs a scan to pin down. There's a speed sensor at each wheel, and they feed the ABS module how fast each wheel is turning, and the car's other systems lean on those readings too, the traction control, the speedometer and on automatics the gearbox shift timing. The sensors sit down by the hubs, exposed to heat, water and road grime, and they fail, the element going or the wiring corroding. When one stops giving a clean signal it trips a warning and takes ABS and traction control offline. A failed sensor doesn't recover, so it needs replacing.
The diagnosis
A diagnostic scan pulled the fault straight to a wheel speed sensor on one corner, no clean signal coming from it, which is exactly what trips the warning and deactivates ABS and traction control. The other three sensors and the brakes themselves checked out, it was that one sensor. That's a sensor replacement on the affected corner, you don't repair a failed speed sensor, so the call was a new genuine sensor, fitted and the codes cleared.
The work
The wheel came off, the failed sensor was removed from the hub, the mounting cleaned up, and a new genuine VW-spec wheel speed sensor fitted and routed properly so the wiring's protected. The system was scanned to confirm a clean signal from all four wheels and the stored fault codes cleared. A road test confirmed the warning light stayed off and the ABS and traction control were active again.
The outcome
No warning light, ABS and traction control back online, the speedometer reading true, and a clean signal from every wheel. The Sharan went home with the systems back to normal. A failed wheel speed sensor takes ABS and traction control offline until it's fixed, so changing it on the affected corner and clearing the codes put the braking systems back where they should be.