What is the immediate consequence of a loss of air pressure in a truck's brake system?

When there is a loss of air pressure in a truck's brake system, the immediate consequence is that the brakes will engage automatically. This is a safety feature designed to prevent the vehicle from rolling or losing control due to a brake failure. In air brake systems, if pressure drops below a certain level, it triggers the emergency brakes to activate, ensuring that the vehicle comes to a stop. This mechanism helps maintain safety even when the air supply is compromised.

Other choices do not accurately represent the direct consequence of a loss of air pressure in the brake system. The brake lights may not necessarily activate as a result of low air pressure; their activation is independent of the air pressure state. Similarly, loss of air pressure does not directly affect steering control, nor does it cause the vehicle to accelerate uncontrollably. Instead, it leads to the automatic application of brakes, which is a crucial safety measure in heavy vehicles equipped with air brake systems.