The brief
The GLA180's dashboard had lit up with a row of warning lights at once: the check-engine light, the ABS light, and a couple of other indicators alongside them. The owner brought it in worried it was something big, with that many lights on. Fair worry, wrong conclusion.
A lot of warning lights showing together usually doesn't mean a lot of faults. It often means one small sensor has stopped sending data that several systems all rely on. When that happens, every system that needed the signal throws its own warning, and the dashboard looks far worse than the actual problem is.
The diagnosis
The scan made it clear. All the warnings traced back to one root: the left front wheel speed sensor had failed, dropping its signal entirely. The codes stacked up from there, an implausible wheel-speed signal logged by the engine and transmission control units, an ABS fault, a traction-control fault, a communication fault with the stability system. One dead sensor, half a dozen complaints downstream.
The wheel speed sensors at the front had both done a lot of years and a lot of road spray, so rather than replace just the failed one and wait for its twin, we did the pair.
The work
The front of the car was lifted, the old sensors and their corroded wiring came off, and a new pair of Mercedes-spec wheel speed sensors went on, each with a fresh O-ring, the harness clipped back into its proper run so it can't chafe.
Then the stored fault codes were cleared on STAR, and the car was driven through a full cycle to let every system see good wheel-speed data again.
After the drive the dashboard was clean, no lights, and nothing came back.
The outcome
Every warning light is off, no codes have returned, and all the systems that lean on wheel-speed data, ABS, traction control, the stability system, are back online and talking.
The GLA180 went home with new front sensors and a clean dashboard, and the owner relieved that the wall of warning lights was one cheap sensor rather than the big fix it looked like. That's the usual shape of it: scary dashboard, small part.