Final answer:
If a low air pressure warning comes on for the Secondary system in a vehicle, the safe response is to stop the vehicle immediately and safely, seeking professional maintenance.
Step-by-step explanation:
When a low air pressure warning comes on for the Secondary system of a vehicle with a dual air brake system, the correct action to take is to stop the vehicle immediately and safely. It is crucial to address the low air pressure issue as the air brake system is essential for the proper and safe functioning of the vehicle’s brakes. Ignoring the warning or continuing to drive could result in brake failure and is extremely dangerous.
Switching to the Primary system or checking the air pressure in the tires does not address the problem with the Secondary system's low air pressure and is therefore not a safe or correct action. After stopping the vehicle, you should seek professional maintenance to resolve the issue.