Despite being very popular issue we would like to explain how to best diagnose the component that has failed, first check for any codes in the suspension module, in most cases if car was let go for a long time with leaking air components, the pump will over heat and break, but if still working oyu have to let it pump up and take the wheel off from the side that's dropping then perform soapy water test , just spray the air bag and see where is bubbles up. if the air bag is not leaking then time to check the air supply line , if that's ok then valve block is next.