Georgia Commercial Driver License Practice Test

When should a low air pressure warning signal activate?

1. When tank pressure exceeds 80 psi

2. When tank pressure falls below 55 psi

3. When the vehicle is at rest

4. When pressing the brake pedal

The correct answer is: When tank pressure falls below 55 psi

The low air pressure warning signal is designed to alert the driver when the air pressure in the system falls to a level that may compromise the safe operation of the vehicle. In commercial vehicles equipped with air brakes, the warning signal activates at a pressure below 55 psi. This threshold is critically important because below this level, the braking systems may not function effectively, increasing the risk of brake failure. When the pressure exceeds 80 psi, there would typically be no reason for a warning signal to engage, as this is well within the operational limits. While the vehicle is at rest or when pressing the brake pedal, those actions do not directly affect the activation of the low air pressure warning signal; the signal is specifically concerned with the overall pressure in the air brake system. This ensures that drivers remain informed about the crucial aspects of air pressure levels while they are operating the vehicle.