What is the correct method to ensure the spring brakes activate?

The method to ensure that the spring brakes activate involves reducing air pressure by pumping the brake pedal. This process is vital because the spring brakes are designed to engage automatically when the air pressure in the braking system drops below a certain threshold, usually due to a failure or malfunction.

When the driver pumps the brake pedal, it helps in depleting the air pressure in the system, demonstrating that the spring brakes can engage as intended when air pressure reaches a critical low point. This action effectively shows the driver that the spring brakes are functioning correctly and can activate when necessary, enhancing safety by preventing a complete loss of braking capability.

The other options do not contribute directly to testing or ensuring the activation of spring brakes. Increasing engine RPMs does not affect the spring brakes; checking fluid levels does not apply as the spring brakes operate on air pressure, and inspecting brake lights pertains to visibility rather than the functionality of the braking system itself.