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One of the switched resistor circuits the battery management system uses to equalise charge between cell groups has failed — open, shorted closed, or drifted in value.

Balancing is the maintenance a traction battery performs on itself, and it works by throwing energy away. Cells in a series string drift apart over thousands of cycles, and because the string is governed by its weakest member in both directions — the lowest group stops the discharge, the highest stops the charge — drift eats usable capacity from both ends. So the module switches a small resistor across the fullest groups near the top of a charge and bleeds them down until the rest catch up.

Which failure it is changes how much it matters, and the two are not close. A circuit stuck open simply stops maintaining that group: capacity ebbs away over months and nothing announces it. A circuit stuck closed is actively destructive — the resistor drains that group continuously, so the module is manufacturing the imbalance it will later report, and the group really does end up weak. It is also a parasitic load that runs with the car parked, which is why it is one of the few pack faults that flattens a traction battery while standing.

Two things are worth confirming before a module is quoted. A drifted bleed resistor still conducts, just too slowly, and presents as a performance fault rather than a circuit one. And a car habitually charged to 80% may never balance at all, because balancing only runs at the top of a charge — a few full charges settle whether the hardware is at fault.