The brief
The Golf's speedometer had stopped working while driving, and the ABS warning light was on. It's a confusing one until you know how it's wired, so a precise diagnosis comes first, and that's what he came in for. There's a wheel speed sensor at each wheel, and they don't just feed the ABS, the car uses those readings for the speedometer too. When one sensor fails, the element going or the wiring corroding down by the hub, the data goes bad, so the speedo drops out and the ABS module shuts the anti-lock 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 why the speedo dropped out and the ABS light came on. 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 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 ABS codes cleared. A road test confirmed the speedometer reading true, the ABS warning light off, and the anti-lock system active.
The outcome
A speedometer that reads true, no ABS warning, the anti-lock braking back online, and a clean signal from every wheel. The Golf went home with the systems back to normal. One failed wheel speed sensor takes the speedo and ABS down together, so changing it on the affected corner and clearing the codes sorted both from a single fix.
