What is the main reason for rejecting a vehicle during the air pressure build-up test?

The primary reason for rejecting a vehicle during the air pressure build-up test is that the pressure must reach the governor cut-out pressure within an acceptable timeframe, typically around 30 seconds. If the pressure takes longer than this to build up, it indicates potential issues with the air system, such as leaks or a malfunctioning compressor, which could hinder safe vehicle operation.

In this context, a build-up time exceeding 30 seconds signals that the air brake system may not be functioning efficiently, affecting the vehicle's ability to stop safely. This timeframe is critical for ensuring that the air brakes are ready to be engaged quickly in emergency situations or when coming to a stop.

The other scenarios might involve different concerns but do not directly indicate that the air pressure system is failing to perform as intended. Therefore, understanding the importance of the correct build-up time helps ensure that the vehicle meets safety standards for operation.