Équipement ajouté non configuré

Something was added to the vehicle after it was built, wired in correctly, and never declared to the vehicle's own software.

A modern vehicle does not discover its own equipment. It is told. Configuration data — held against the vehicle identification number by the manufacturer and written into the modules — states what this vehicle has: how many doors, whether there is a towbar, a reversing camera, upgraded lighting, rear entertainment, a parking heater, a gas conversion. Every module that needs to know is given the relevant part of that list.

So fitting the hardware is half the job, and the half that gets skipped is the invisible one. A towbar loom that works perfectly will still leave the vehicle unable to suppress its parking sensors or adjust its stability control for a trailer. A camera that produces a picture will not appear on a screen that has not been told to expect it.

Two failure shapes follow, and they look different from each other.

Equipment that is fitted but ignored — the commonest, and the one the owner notices immediately.

Equipment the vehicle now expects and cannot find, which happens when a used module arrives carrying a better-equipped donor's configuration. That one produces permanent fault codes for hardware that does not exist, and no amount of testing finds anything, because there is nothing there. An exhaustive search that turns up nothing is itself the answer, and the next step is the vehicle's build record rather than more looking.

The remedy is coding rather than parts, and it usually needs manufacturer-level access. The person who fitted the equipment is normally better placed than a franchised dealer, because they know what was installed and where their wiring meets the vehicle's.