What is the function of low-air warning devices during the air brake check?

The function of low-air warning devices during the air brake check is to alert the driver when air pressure drops below a safe level. This is crucial for ensuring the safety of the vehicle and its occupants, as adequate air pressure is necessary for the proper functioning of the air brake system. When the air pressure falls below a certain threshold, the warning device activates—typically through a light or audible alarm—which warns the driver to take action before the brakes can fail. This preventative measure helps in maintaining control of the vehicle and preventing potentially dangerous situations due to brake failure caused by low air pressure.

The other choices do not directly address the role of low-air warning devices during the air brake check; they instead refer to unrelated issues such as high air pressure, emergency brake signals, or battery health, which are not monitored by low-air warning devices.