How does a driver test that the low air pressure warning signal is working correctly during a pre-trip inspection?

Explanation

A driver tests the low air pressure warning signal by shutting the engine off with enough air pressure that the warning is not lit, turning on electrical power, and pumping the brake pedal repeatedly to work tank pressure down, confirming that the warning activates before pressure falls below 60 psi. 49 CFR 383.111(b)(5)(iii) specifically requires CDL applicants to know about low pressure warning alarms as part of safe and accurate pre-trip inspection procedures, a direct match for this exact test; the 60 psi threshold itself is reused from FMVSS No. 121, codified at 49 CFR 571.121 S5.1.5. Checking only at highway engine speed is wrong because the test is deliberately run with the engine off, to isolate the warning system from normal compressor operation. Watching for an unrelated dashboard chime is wrong because the low air warning is tied to air pressure specifically, not a generic alert. Draining all tanks to zero is wrong and unsafe; the test only needs pressure reduced into the warning's activation range, not a complete air loss.

Source: 49 CFR 383.111(b)(5)(iii)