On 08/07/2021 at approximately 3 pm while driving the vehicle low brake fluid level light indicated on dashboard. Stopped at a gas station and checked to make sure there was no brake fluid leaking and checked brake fluid level which was low. The cars brakes were still operating properly and we returned to the location we were staying to find an auto parts store to purchase brake fluid. At 6 pm, drove to the auto parts store to get brake fluid. We purchased the appropriate fluid and topped of the brake fluid reservoir. The low brake fluid light turned off on the dash after topping off the brake fluid. About 2 ounces were added. Upon leaving the auto parts store, we pulled out onto the road and when trying to brake, the brakes malfunctioned, the pedal went completely to the floor and the car did not stop normally and hit another vehicle. Police report attached. No injuries and minor damage to both vehicles bumpers Car was pulled off the road and was towed to shop for inspection as the brakes would not stop the car. Shop #1 replaced the master cylinder and the brakes still did not operate properly. Car was towed to shop #2 (Ford Dealer) and they diagnosed it as a failed ABS HCU unit in the vehicle that was not communicating with the onboard computer system. ABS HCU was replaced by the Ford Dealer and vehicle is now braking as normal. There were no warnings from the vehicle computer system that there were any issues with the brakes other than the low brake fluid lev