Service Air Suspension?

[HUMTECH]

If your getting A serv air susp message with the cap off likely the valve is leaking, the cap will seal off this leak enough to not cause A problem, if the compressor has to run continuously to keep up with the leak it will set an overheat code and shut the compressor down to cool it. Also could throw an exhaust solenoid code thinking the system is exhausting. Simply take the cap off and put some water in the valve and watch for bubbles(not the cheerleader next door).