The brief
Mr Anthony's CLA180 wouldn't start, and the obvious suspect was the battery, but a no-start with a spread of unrelated fault codes usually points somewhere else, so it came in for a proper scan rather than a guess at a new battery. A modern Mercedes routes a lot of its power through the fuse box, and that box has connections and internals that can wear, corrode or develop a bad contact over the years. When it does, the power supply to the systems that need it goes intermittent, the car logs a low power supply fault, throws odd codes for things like the headlight beam, and won't start because the ignition circuit isn't getting what it needs. A worn fuse box doesn't recover, so it gets replaced.
The diagnosis
The scan put up a power supply low fault along with a scatter of other codes, including a headlight beam fault, the kind of mixed picture that says the power distribution is the problem, not one component. The fault was traced to a worn fuse box, which is why the ignition circuit and various systems weren't getting clean power. The battery itself was fine. That's a fuse box replacement, rather than a battery that wasn't the cause.
The work
The worn fuse box was removed and a new genuine Mercedes-spec fuse box fitted, the fuses and relays transferred across correctly and the connections checked clean and tight. The fault codes were cleared and every affected system checked, the ignition circuit, the lights, the rest, all getting clean power now. A road test confirmed the car starting first time, every system working, the lights behaving normally, and no fault codes.
The outcome
The CLA180 starting first time, every electrical system working, the headlights behaving normally, and no fault codes. Mr Anthony got the car back the same day, roaring back to life after the QC check. Reading the scan properly meant we found the worn fuse box rather than throwing a battery at it, which is the difference between fixing a no-start and just delaying it.
