Boordlader defect

The unit that converts alternating current from a domestic or public supply into the direct current a traction battery can accept has failed.

Its scope is narrower than people assume, and knowing the boundary saves a great deal of misdiagnosis. It handles AC charging only — a home socket, a wallbox, a street post. Rapid DC charging bypasses it entirely, because the charge point does the conversion itself and feeds the pack directly.

Which gives the single most useful diagnostic in the whole charging system, and it costs nothing: try both kinds. A car that rapid-charges perfectly and refuses every AC supply has a fault in the on-board charger or its path. A car that fails on both has a fault somewhere they share — the inlet, the contactors, the pack, or the control electronics. One test, and the problem is halved.

The unit is liquid-cooled on most vehicles and works hard for hours at a time, so its failures are often thermal: reduced charging rate before outright failure, worse in summer, worse again if the electronics coolant circuit is low or airlocked. A charger that has become slow rather than dead is worth investigating as a cooling fault before it is condemned.

It is rarely a serviceable item — usually a sealed assembly, sometimes integrated with the DC/DC converter into one unit, which is worth establishing before comparing quotes because it changes what is actually being replaced.