PCT No. PCT/GB96/01731 Sec. 371 Date Apr. 17, 1998 Sec. 102(e) Date Apr. 17, 1998 PCT Filed Jul. 18, 1996 PCT Pub. No. WO97/05001 PCT Pub. Date Feb. 13, 1997A vehicle braking system in which a stored volume of working fluid is used by a brake control system to apply the brakes under the control of an electronic control unit. The stored volume is replenished by pumping additional working fluid using a pump driven by an electric motor. The electric motor is periodically energized. An inferred value is established for the accumulator pressure based on an assessment of the motor response during the periods of energization. The electric motor can be arranged to be energized for short periods at predetermined intervals and the motor response during these periods assessed. From this assessment, either the switch-on point for driving the pump motor for the purpose of recharging the stored volume of working fluid is determined from the level of motor torque applied during the short periods of energization, or, where the system includes a pressure sensor for detecting the working fluid pressure, a signal for corroborating the signal of the pressure sensor is established from the level of motor torque applied during the short periods of energization.