1996 BMW 740iL ABS Hydraulic Pump Replacement Cost

Anti-lock brake (ABS) systems use hydraulic valves to send pressurized brake fluid to the service brakes in quick spurts to prevent the wheels from locking during hard braking. Since the pressure required to operate this system must be constantly regenerated, an ABS hydraulic pump is used. The ABS pump maintains the brake fluid pressure in the ABS hydraulic unit, and allows continuous operation of the ABS system without the need to repeatedly press the brakes.

When the brake system is filled with brake fluid, the ABS hydraulic unit fills at the same time, and the brake fluid inside the hydraulic unit is sufficient to actuate the brakes on demand. The ABS hydraulic pump pressurizes the fluid needed to actuate the brake system in quick intervals, and that pressure travels through the hydraulic valves when those valves are opened by the ABS control module. Depressurized brake fluid returns to the pump to be repressurized for continued use. Without the ABS pump, the driver would have to pump the brake pedal faster than humanly possible.

When the ABS hydraulic pump has failed, the driver will be prompted with an ABS system warning light, and, in most vehicles, the brake system warning light as well. The anti-lock brake system will fail to function in emergency situations, and the vehicle will feel less stable and more prone to skidding in rain, sleet, or snow.

After driving a vehicle for any length of time, the driver will become accustomed to the road manners of that vehicle, and sudden changes to safety features and driver assistance systems may lead to unpredictable operation. That being said, the normal brakes will be functional when the ABS hydraulic pump is faulty, but the vehicle will be prone to skidding in an emergency situation or during inclement weather. As a general rule, if the brake or ABS warning lights appear, or the brakes do not function properly, the vehicle should be serviced immediately.

ABS hydraulic pumps do fail, but failure is sporadic at best, and better considered unpredictable. Most vehicles will be sent to the scrap yard with the same ABS pump that was installed at the factory, but some will not be so lucky. In general, ABS pump failure in the first several years of a vehicle's life is unexpected. Later in the useful life of a vehicle, maintenance is key to ensuring the brake system and ABS system are kept in working order - this includes the ABS pump.

Most vehicles with anti-lock brakes will offer an indication of what is happening when the ABS system has stopped functioning properly. When this is the case, the technician will begin by reading trouble codes, and may notice a code referring to low brake fluid pressure. When this is realized, the ABS pump motor and brake fluid pressure sensor are tested. In most vehicles, a jumper wire can be used to send power to the ABS hydraulic pump motor, even when the vehicle is off. If the motor fails to run when provided with power and ground, the motor is diagnosed as defective.

Some vehicles have an all inclusive ABS unit which includes the ABS modulator assembly, ABS hydraulic pump, and ABS electronic control module. On these vehicles, the entire ABS unit may need to be replaced by disconnecting the ABS unit electrically and hydraulically from the vehicle, of course, after the negative battery terminal is disconnected. Other vehicles, especially earlier models, allow for replacement of the ABS hydraulic pump motor by disconnecting the pump motor electronically, removing fasteners, and simply pulling the electric motor from the ABS unit.

Flush and refill the entire brake system when replacing major components. Any debris or contamination from these components may remain in the system and cause repeat failures. Also, the amount of air entering the brake system and ABS system dictates that the system is thoroughly bled to ensure the service brakes remain operational.

Removal of the ABS pump motor of ABS hydraulic unit are two very different operations, and understanding which procedure is necessary to fix a faulty ABS hydraulic pump is mandatory. Using a service manual is the only sure way to determine which procedure the vehicle requires, and guessing may result in additional work, or additional cost.

Replacing the ABS hydraulic pump is not a difficult task, but a thorough knowledge of hydraulic brake systems and anti-lock brake systems is necessary. Diagnosis can be reached easily with a service manual specific to the vehicle, but opening the brake system, especially at this high pressure area, can cause injury or render the service brakes useless. If you have any concerns about completing the task, or lack the experience needed, allow a professional to handle this repair.