What is the first action to take during the low air pressure alarm test?

The first action to take during the low air pressure alarm test is to pump down the service brake. This step is critical because it reduces the air pressure in the system, allowing the low air pressure alarm to activate, which verifies that the alarm is functioning properly. By intentionally lowering the pressure, you are ensuring that the system is responsive to its own warning mechanisms.

Starting the engine, releasing the air brakes, or checking for warning lights are actions that can be taken later in the process, but they do not initiate the low air pressure alarm test. Pumping down the service brake is a proactive measure that directly relates to testing the warning system’s ability to alert the driver of low air pressure, which is essential for maintaining safety on the road.