I have had issues for a while with air suspension being the proper height. The vehicle enters extended mode often. Most of the time the system lowers to normal height when driven at or above 35 mph for a while. The front axle performs fine and seems to raise and lower at the proper rate. The rear, however, will not lower properly, and I believe that is what is making it go into extended mode. I was under the assumption that it was not letting the air escape the rear, so I replace the reservoir valve block, and rear valve block. Also, I replaced compressor desiccant and filters in the air dryer. The old desiccant had degraded quite a bit.
After talking with a tech about it possibly being height sensors, I went to run a calibration. When it went from off road height to access height during the calibration process, it wouldn't lower and had to abort the calibration process. I did get a code at that point. C1A13-64. "Pressure does not decrease when venting gallery"


After reenabling the air suspension after the failed calibration, I tried to lower the vehicle, while watching a live feed of the ride height sensors. I've attached a screen shot from that. The front immediately lowers, and the back starts to rise without going down at all, which matched what I am physically seeing, which would make me think the ride height sensors are working properly. At that point, the display read "suspension in extended mode". Is the weight of the vehicle in the front sufficient that if the gallery isn't properly vented, the air from the front can cause the rear to rise?
I'm thinking it must be the exhaust valve that is part of the compressor keeping air from exiting fast enough for the vehicle to recognize it is lowering. I'm unsure how to proceed with testing or verifying this idea. Is there another explanation for this that I'm not seeing?

 

You rear block is likely the issue. It is not OEM, hooked up wrong, or not specific to the rear. The front and rears can not be swapped but sellers or non-OEM will sell them for either location.