The brief
Mr Alex's C200 AMG had the check engine light on. A check engine light can come from a long list of things, so the first job is a proper read, not a guess. He brought it in. We ran the Mercedes diagnostic system on it, because a generic code reader gives you a rough code, but the manufacturer software gives you the live data and the freeze-frame behind it, which is what tells you whether a sensor is actually faulty or just reporting a fault upstream. The light is the car telling you something is outside spec, and ignoring it lets a small fault turn into a driveability problem or a part that takes others down with it, so it needed reading and fixing at the source.
The diagnosis
The Mercedes diagnostic pulled the stored fault and the live data showed the mass air flow sensor reading off, the airflow figure not matching what the engine was actually doing, which throws the fuel mixture out and sets the light. Wiring and connectors to it checked out, the sensor itself was the fault. A mass air flow sensor that's drifted doesn't come back, so the call was to replace it and reset the engine's fuel adaptations so it relearns on a sensor it can trust.
The work
The old mass air flow sensor was removed and a new genuine Mercedes-spec sensor fitted, the intake checked for leaks while it was apart so nothing was throwing the new sensor off. The fault was cleared, the engine's fuel adaptations reset, and the air filter checked since a clogged one makes a MAF's life harder. A road test confirmed the light stayed off, the idle steady, and the throttle response back to normal with no hesitation.
The outcome
No check engine light, a steady idle, clean throttle response, smooth power, and the fuel trims back in range. The C200 went home running properly with the light out. Reading it on the Mercedes system meant we replaced the part that was actually faulty rather than throwing parts at a generic code, so it was one visit and done.
