Electrohydraulic antilock brake system with isolation valve

An antilock brake system for a vehicle may include a controller that is linked to a brake pedal sensor. The brake pedal sensor may be linked to a brake pedal. The brake pedal may be coupled to a normally closed brake pedal valve. The brake pedal valve may include an inlet in communication with a source of pressurized hydraulic fluid and an outlet in communication with a normally opened isolation valve. The isolation valve may be in communication with one or more main control valve systems and may be linked to a controller which maintains the isolation valve in a closed position during normal operating conditions. The isolation valve then shifts to an open position in the event current supply by the controller is interrupted as a result of an electrical failure or malfunction of the controller.