Your vehicle uses a hybrid technology known as regenerative braking. This technology enables the electric drive motor on your vehicle to operate as a generator when you are coasting or braking. The energy of the moving vehicle is used to recharge the vehicle's high voltage hybrid battery.
The conventional hydraulic disc brakes on your vehicle work in partnership with the regenerative braking to insure effective braking in all situations, such as when the high voltage hybrid battery is fully charged or a high braking demand is requested. Four wheel, four channel ABS allows the vehicle to maintain steering control during braking and Electronic Stability Control (ESC) helps you to keep your vehicle in control in unfavorable conditions. These systems, however, are not a substitute for safe driving practices.
The braking system is computer controlled and uses the information provided by the driver's input at the brake pedal to seamlessly blend the regenerative braking with the conventional hydraulic disc brakes to meet any requirements for deceleration. The brake controller in your vehicle has a high pressure accumulator to provide the hydraulic pressure to the disc brakes in response to the driver's input. The controller interprets the braking request and uses regenerative braking, conventional hydraulic braking or a combination of both as necessary. Since the controller applies the hydraulic brakes through its high pressure accumulator, you may occasionally hear the motor driven pump in the controller when it runs to recharge the system. This recharging cycle is normal.
Even though the conventional disc brakes are operated by the controller, there is still a direct mechanical connection with the brake pedal and the hydraulic brake system in the unlikely event of a controller problem. See "Warning Lights, Gages, and Indicators" and "Driver Information Center (DIC)" in the Index of the vehicle's owner manual. In the event of a controller problem, your brake pedal may be harder to push and the stopping distance may be longer.