Gallery: 2024 Chevrolet Trailblazer 28Fluid Problem Becomes Big RepairLosser traced the pressure problem back to brake fluid he said had gone unserviced for an extended period. The shop said the degraded fluid contributed to the failure of the master cylinder, which controls hydraulic pressure throughout the braking system. Material from that damaged component then reportedly traveled into the ABS hydraulic unit and interfered with the system’s ability to release pressure after the driver lifted off the pedal. Debris from the failing master cylinder clogged the ABS hydraulic unit, preventing the brakes from fully releasing. Losser said the first day was spent identifying the brake-pressure problem and locating a used ABS hydraulic unit.