What happens if the trailer does not move when gently pulling on it during an emergency brakes test?

When you gently pull on the trailer during an emergency brake test and it does not move, this indicates that the trailer brakes are functioning properly. Properly functioning trailer brakes will hold the trailer in place when the truck's braking system engages. This is a critical safety feature, as it ensures that the trailer will not roll away, particularly in situations where the truck is stopped and the brakes are applied.

In such a test, if the trailer remained stationary, it demonstrates that the braking mechanism is effectively applying enough force to the wheels of the trailer to prevent movement. The truck and trailer are designed to work together, and effective braking is essential for maintaining control.

The other options involve conditions that would not support this positive outcome. For instance, if the air pressure were too low, the brakes might not engage as required, leading to movement rather than stability. Likewise, if the trailer were not connected correctly, there would be no effective braking force applied since the attachments would prevent proper coordination between the truck and trailer. Similarly, if the dolly required adjustment, this could indicate that the connection was not functioning correctly, affecting the overall brake effectiveness. Thus, the correct scenario confirms the proper operation of the trailer brakes.