What must be checked regarding valve stems?

The focus of this question is on the importance of the presence and condition of valve caps during the pre-trip inspection of a vehicle's tires. Valve stems are critical components that allow air to enter and exit the tire; valve caps play a key role in maintaining the integrity of these systems.

A properly secured valve cap serves several purposes: it prevents dirt, moisture, and debris from entering the valve stem, which could result in air leaks or damage. If the caps are missing or broken, it can lead to a slow loss of tire pressure, compromising safety and performance while driving.

Regularly checking the condition of valve caps during the pre-trip inspection helps ensure that all elements related to tire performance are functioning correctly, thus enhancing safety on the road. This aligns with best practices for vehicle maintenance and safety checks, reinforcing the importance of thorough inspections before operating a vehicle.

In this context, while the other options might touch on aspects of tire and valve maintenance, they do not address the critical nature of ensuring that the valve caps are intact and functional.