The brief
Mr Chia's 316i came in with the steering gone heavy, harder work than it should be. He brought it in, and the way to track that down is to read the fault codes rather than guess, because heavy steering can come from a few directions. The ABS pump control unit runs the anti-lock brakes and the stability system, and it leans on the wheel speed sensors at each corner for its information. Often when there's an ABS-related fault, replacing a faulty wheel speed sensor fixes it. But sometimes the fault is the control unit itself, and when the ABS and stability system drops out, related systems can step back into a safe mode that leaves the steering feeling heavy. A failed control unit doesn't recover, so it gets replaced and coded to the car.
The diagnosis
The fault codes told the story: not the usual wheel speed sensor this time, but the ABS pump control unit itself, which is why the steering had gone heavy. The wheel speed sensors and the wiring were fine, the control unit was the fault. That's an ABS pump control unit replacement with coding to the car, rather than a wheel speed sensor that wasn't the problem.
The work
The faulty ABS pump control unit was removed and a new genuine BMW unit fitted, every fastener and brake line torqued to the manual figures, and the unit coded and programmed into the car's systems so it talks to the rest of the network. The brakes were bled, the fault codes cleared, and every related system checked. A road test confirmed the steering back to normal weight, the ABS and stability system working, no fault codes, and no warning lights.
The outcome
The steering back to its normal, light weight, the ABS and stability system working as they should, no fault codes, and no warning lights. Mr Chia got the 316i back driving normally again. Reading the codes properly meant we replaced the control unit that had actually failed rather than throwing a wheel speed sensor at it, and coding the new unit in is what brings the systems back online.