Why does the BMW E66 ABS pump keep making noise?
2 Answers
It is normal for the BMW E66 ABS pump to keep making noise. When the ABS is working, the reaction sleeve moves left and right, and the driver can feel the vibration of the pedal underfoot and hear some noise. Composition of the ABS system: The ABS system mainly consists of 4 parts: wheel speed sensor, electronic control unit (ECU), hydraulic unit, and ABS warning light. The wheel speed sensor detects the motion state of the wheel and sends out a sinusoidal electronic pulse AC signal. After being processed by the modulator, the pulse is converted into a digital signal and transmitted to the electronic control unit. The electronic central control unit (ECU) receives the input signal from the wheel speed sensor, calculates the wheel speed, vehicle speed, and slip ratio based on this parameter, and determines the wheel state according to the slip ratio, then issues control commands to the hydraulic unit. The hydraulic unit adjusts the pressure of the brake pipeline according to the control commands. The adjustment process includes pressure holding, pressure increase, and pressure decrease. The ABS warning light is used to alert the driver to any system faults. Working principle of ABS: During braking, the ABS quickly determines the wheel lock state based on the speed signal from each wheel speed sensor, closes the normally open input solenoid valve on the wheel that is starting to lock, and keeps the braking force unchanged. If the wheel continues to lock, the normally closed output solenoid valve is opened, and the braking pressure on this wheel rapidly decreases due to the direct connection to the brake fluid reservoir, preventing the wheel from completely locking due to excessive braking force. This keeps the braking state always at the optimal point (slip ratio S of 20%), achieving the best braking effect and the safest driving.
This is likely a failure of the ABS pump motor. My car also made this continuous noise before, and the inspection later revealed it was an issue with the pump motor itself. The ABS pump in BMW E66 models is prone to motor seizure due to aging or water ingress, causing a continuous humming sound when it keeps running. Another common cause is electrical wiring problems, such as a blown fuse or poor relay contact, which keeps the pump running non-stop. Additionally, a faulty pressure switch can cause the system to mistakenly maintain pressure, leading to continuous pump operation. In more severe cases, it could be an internal short circuit in the ABS control module. BMW's electronic systems are complex, and software errors can also trigger such issues. If you encounter this problem, it's best not to delay—immediately turn off the engine and check if the battery voltage is stable. First, remove the pump's fuse to disable the ABS, then take the car to a professional workshop for a diagnostic scan to identify the fault codes. Avoid driving under these conditions as ABS failure can compromise braking performance. Regular maintenance and inspection of related components can also help prevent such issues.
