Parts
Modules and wiring: how each one fails
What each module actually does, how it fails, and what gets replaced first by mistake.
BDC (body domain controller)Also called: BDC_BODY, body domain controller
The FEM's successor — body functions, access, immobilizer and gateway in one domain module, from the 2014 X5 and BMW/Mini front-drive cars to the G-series.
CAS (Car Access System)Also called: CAS2, CAS3, CAS3+, CAS4, immobilizer module
The gatekeeper on E-series BMWs and the F01/F10/F25 family — ignition switch, key check, immobilizer and terminal control in one module.
FEM (front electronic module)Also called: FEM_BODY, front electronic module
The F30-generation body module — it took over the footwell module, the Car Access System, the junction box and the central gateway in one unit.
FRM (footwell module)Also called: FRM, FRM2, FRM3, footwell module, light module
The footwell module on E-series BMWs, Mini R5x and the F01/F10/F25 family — exterior lights, front windows, mirrors — and the module that can corrupt itself when voltage drops.
IBS (intelligent battery sensor)Also called: battery sensor, negative terminal sensor
The sensor on the battery negative terminal that runs the whole charging strategy — and the reason a new battery needs registering.
JBE (junction box electronics)Also called: junction box, junction box electronics
The E90-generation junction box module — wipers, rear windows, locking, heating outputs and a gateway role — so one fault shows up as half the car complaining at once.
SZL (steering column switch centre)Also called: steering column switch cluster, clock spring, steering angle sensor
The switch cluster and clock spring behind the steering wheel — turn signal and wiper stalks, wheel buttons and the airbag feed pass through it, and the steering angle sensor lives in it.