The brief
Eric's 328i had a fault code displayed on the dash and the driving stabilization, the ABS and the stability control, dropping out. He brought it in for a check. That kind of stability fault usually traces back to a wheel speed sensor. The wheel speed sensors tell the ABS and stability module how fast each wheel is turning so they can step in if one locks under braking or spins under power. They 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 the module can't trust the data, so it shuts ABS and stability control down and lights the dash. 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 stability fault. 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 ABS sensor was removed from the hub, the mounting cleaned up, and a new genuine BMW-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 ABS and stability codes cleared. A road test confirmed the stability fault stayed off and the ABS and stability control were active again.
The outcome
No stability fault, the ABS and stability control back online, and a clean signal from every wheel. The 328i went home with the driving stabilization working again. A failed wheel speed sensor takes ABS and stability 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.
