ABS Accumulator: A high pressure electric pump is used in some ABS systems to generate power assist for normal braking as well as the reapplication of brake pressure during ABS braking. In some systems, it is used only for the reapplication of pressure during ABS braking.

The pump motor is energized via a relay that is switched on and off by the ABS control module. The fluid pressure that is generated by the pump is stored in the "accumulator." The accumulator on ABS systems where the hydraulic modulator is part of the master cylinder assembly consists of a pressure storage chamber filled with nitrogen gas. Should the pump fail (a warning light comes on when reserve pressure drops too low), there is usually enough reserve pressure in the accumulator for 10 to 20 power-assisted stops. After that, there is no power assist. The brakes still work, but with increased effort.

On ABS systems that have a conventional master cylinder and vacuum booster for power assist, a small accumulator or pair of accumulators may be used as temporary holding reservoirs for brake fluid during the hold-release-reapply cycle. This type of accumulator typically uses a spring loaded diaphragm rather than a nitrogen charged chamber to store pressure.