The brief
Mr Eric's 5 Series came in with a parking brake fault code, the dash reporting the parking brake had failed. The parking brake is what holds the car when it's parked, so a failure there isn't one to leave, and it gets read properly to find which part has gone. This car has an electric parking brake, applied by small motorised actuators rather than a cable, one at each rear wheel. The actuator has gears and a motor that work every time you park, and over the years one can wear out or seize, so it stops applying or releasing properly and the system flags a parking brake failure. A failed actuator doesn't recover, so it gets replaced and the parking brake calibrated.
The diagnosis
The BMW handset read the fault and pinned it to the left parking brake actuator, which had failed, which is the parking brake failure message. The right actuator, the switch and the wiring were fine. That's a left parking brake actuator replacement with the system calibrated, rather than chasing a parking brake fault around the car.
The work
The failed left parking brake actuator was removed and a new genuine BMW-spec actuator fitted, every fastener torqued to the manual figures and the connections checked. The parking brake was then calibrated with the diagnostic system so both sides apply and release evenly, and the fault code cleared. A road test confirmed the parking brake applying and releasing properly, holding the car on a slope, no fault code, and no warning lights.
The outcome
The parking brake applying and releasing properly, holding firmly on a slope, no parking brake failure message, and no warning lights. Mr Eric got the 5 Series back with the parking brake working as it should. Reading the fault properly meant we replaced the actuator that had actually failed rather than guessing, and calibrating it afterwards is what makes both sides hold evenly.