Air Brake System With External Fill (Shrader) Valve

If your engine will not start and it is desirable to release the parking brake, do the following: Block the wheels. Turn the ignition switch to the ON position. Fill the air reservoir for the braking system by external means. The parking brake will not release until air pressure reaches 65 psi (448 kPa). The low air buzzer will sound until air pressure reaches 65 psi (448 kPa) with the ignition switch in the ON position.