What can happen if the air pressure drops too low in an air brake system?

In an air brake system, maintaining proper air pressure is crucial for safe and effective braking performance. If the air pressure drops too low, the brake system can fail to engage properly, leading to inadequate stopping power. Air brakes rely on compressed air to function effectively; therefore, insufficient air pressure compromises the ability of the brake components, such as the brake chamber, to create the necessary force to apply the brakes. This situation can create a significant safety risk, as the driver may not be able to slow down or stop the vehicle promptly, potentially leading to accidents or loss of vehicle control.

The other options relate to different systems or functions of the vehicle, which do not directly impact the performance of the air brake system in such a critical manner. Thus, low air pressure primarily affects brake engagement, making it the correct answer to the question.