What happens if air bag loses air?

If the system loses air, troubleshooting is easy because it can be only one of three things; the air spring fitting, the fill valve or the air spring itself. First thing to check is the seal of the air spring fitting to make sure it is sealed by simply pouring water on the area. If it bubbles, pull the fitting out, re-coat it with Teflon tape or standard pipe fitters dope and re-install (torque it to 20 ft./lbs). Next item to check is the fill valve by spraying soapy water on the area with the cap removed. If it bubbles, replace the fill valve core by simply sticking the topside of the cap onto the valve core and spinning counter clockwise to remove it. It can be found at most auto parts stores or by contacting Trailair. If the first two are not leaking then the air spring is not holding air and a replacement should be obtained directly from Trailair.