Final answer:
A combination vehicle air brake system should not leak more than 2 PSI in one minute when the engine is off, the brakes are released, and your foot is on the brake pedal.
Step-by-step explanation:
A combination vehicle air brake system should not leak more than 2 PSI (pounds per square inch) in one minute when the engine is off, the brakes are released, and your foot is on the brake pedal. The air brake system in a combination vehicle uses Pascal's principle, which states that pressure applied to a fluid is transmitted equally in all directions. This principle allows the force exerted by the brake pedal to be transmitted to the wheel cylinders, generating the necessary force to stop the vehicle.