The brief
The CLA180 had its ABS warning light on. The right diagnostic is what saves you from replacing parts you don't need, so the team scanned it properly rather than guessing. He brought it in. The ABS warning usually means a wheel speed sensor. There's one at each wheel, and they tell the ABS module how fast each wheel is turning so it can step in if one locks under hard braking. 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 the module can't trust the data, so it shuts ABS down and lights the dash. An accurate scan tells you which sensor, so you change that one and nothing else.
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 ABS light. The other three sensors, the wiring and the brakes themselves checked out, it was that one sensor and nothing more. 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, no other parts touched.
The work
The wheel came off, the failed ABS sensor was removed from the hub, the mounting cleaned up, and a new genuine Mercedes-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 ABS warning light stayed off and the anti-lock system was active.
The outcome
No ABS warning, the anti-lock braking back online, a clean signal from every wheel, and only the one part that needed changing replaced. The CLA180 went home with the safety system working again. An accurate diagnosis pinpointed the faulty sensor, so changing that one and clearing the codes put the braking system right without changing anything that didn't need it.