My son gas a 2016 2.5 colorado. 45k miles. He was coming home the other day and his brakes went out. (Pedal could not be pushed). Solid as a rock. We replaced the check valve no change got a little better when we bleed the lines. (Truck was purchased new. No work done the brakes.) The fluid is rusty colored so we changed the fluid. Some better. It is still far from normal. We tested the brake booster and it didnt seem to be bad. We pulled the check valve off and it had no vacuum. I cant detect a leak anywhere. Can some one offer suggestions.