The brief
The 528i's electric parking brake had started playing up: it wouldn't apply or release reliably, sometimes a grind from the rear when it tried, and a parking brake warning on the dash. He brought it in. A parking brake that won't hold is a safety issue and one that won't release leaves the car going nowhere, so it wants fixing. The electric parking brake uses an actuator, a motor and gearbox that pulls the brake on and off, either built into the rear calipers or as a central unit driving cables, with a control module behind it. The actuator's motor and gears wear, so it stops applying or releasing cleanly, which is the unreliable behaviour, the grind, and the warning. A failed parking brake actuator doesn't recover, so it needs replacing, then coded to the car and the system reset.
The diagnosis
A diagnostic scan pulled the fault to the parking brake actuator, not driving the brake cleanly, which is exactly the unreliable apply and release. The rear brakes themselves and the wiring checked out, it was the actuator at fault. That's an actuator replacement, you don't rebuild it on the car, so the call was a complete unit, fitted, coded to the car, and the parking brake system reset and recalibrated.
The work
The old parking brake actuator was removed and a new genuine BMW-spec unit fitted, connected up, every fastener torqued to spec. The new actuator was coded to the car so the module recognised it, the parking brake system reset and recalibrated through the proper procedure, and the stored faults cleared. A check confirmed the parking brake applied and released reliably from the switch, held the car firmly, and released cleanly, with the warning gone.
The outcome
An electric parking brake that applies and releases reliably, holds the car firmly, releases cleanly, and does it without a warning on the dash. The 528i went home with the parking brake sorted. A failed actuator only gets less reliable until the brake won't hold or won't release, so changing it, coding it in and resetting the system put it right.
