What might indicate air in the hydraulic system during a brake check?

A spongy action of brake pedals is a clear indication of air in the hydraulic system during a brake check because the presence of air bubbles in the hydraulic fluid disrupts the system's ability to transmit force effectively. When the brake pedal is pressed, the hydraulic fluid should create a firm, direct response due to the incompressibility of liquids. However, when air is introduced into the system, it creates compressible spaces that prevent the brake fluid from transmitting pressure uniformly. This results in a sensation of sponginess or vagueness in the pedal's feel, which suggests that the hydraulic system may need to be bled to remove the entrapped air and restore proper function.

In contrast, excessive noise from the brake unit is more commonly associated with mechanical issues or low fluid levels rather than air in the system. Hard pressure when applying brakes suggests that the system is functioning correctly and that the brake fluid is free of air. Lastly, inconsistencies in brake fluid levels may point to leaks or other issues but do not directly indicate air present in the system during a pedal check.