sagged envoy suspension

My 2003 GMC Envoy suspension on the rear is not leveling it 's sitting low the air runs and shuts off no leaks visable and the compressor seams to pump air when the hose is attached and my thumb is over the end of the hose the gauge raises quickly. not sure what may be involved in air syatem were could the sensors be or moduals . thanks
Andy

The bags themselves could be leaking which may not be visible. Best way to spot a leak is to mix some soapy water into a spray bottle and squirt it onto the air lines...use stream not spray nozzle setting. The Envoy suspension will attempt to level for a certain time period and then quit when it doesn't receive response from the leveling sensor.

This thread shoud be moved to the Envoy section...more knowing people will see it there.