FRM (footwell module)

The FRM sits in the driver-side footwell. BMW's own E90 training lists its jobs: all exterior lights and the adaptive headlights, the front power windows with their anti-trap, the electric load shut-down, and the inputs from the door contacts and lock cylinders. It is also the gateway between the K-CAN and the LIN bus that serves the mirrors and the driver's switch block, and it stores a copy of the vehicle order.

What it does not do on that car matters just as much: the CAS is the master for central locking, and the junction box (JBE) drives the locks, the rear windows and the wipers. When "everything electrical" dies at once, knowing that split is half the diagnosis.

The failure this module is known for is data corruption: a voltage drop during a battery change or a jump start, or an interrupted coding session, can corrupt its memory, and the module stops working.

The symptom set looks unrelated until you know the module: headlights stuck on or dead, front windows that will not move, turn signals inoperative, mirrors frozen. The common mistake is replacing the part that shows the symptom — a window regulator, a light switch, a battery — when the module itself is the fault. A used module from another car is not plug-and-play and has to be programmed to the car; repairing the original avoids that.

On a Mini R55 or R56, check the VIN for MINI safety recall 23V-337 first: it covers the footwell module on R56 Hardtops built November 2006 to November 2013 and R55 Clubmans built July 2007 to June 2014 that were sold or registered in road-salt states, because the module can corrode over time and short-circuit.