If a low air pressure warning comes on for only one air brake system, what should you do?

Answer: D — Stop, safely park, and continue only after the system is fixed

When a low air pressure warning is triggered for one air brake system, the most prudent course of action is to stop and safely park the vehicle until the issue is resolved. This is because a low air pressure warning indicates that one of the critical systems is not functioning correctly, which could compromise the vehicle's braking ability and overall safety. Continuing to drive without addressing the low air pressure can lead to brake failure, making it difficult to stop the vehicle safely, especially in emergency situations. Furthermore, air brake systems are designed with a dual system for safety, so if one system is compromised, the remaining system might not be sufficient to stop the vehicle effectively under all conditions. The option to reduce speed and drive to a garage or test the remaining system while under way might seem tempting but increases the risk of losing braking capacity. Therefore, the best and safest action is to ensure that the vehicle is parked and the air brake system is thoroughly inspected and repaired before continuing on the road.