If the vent solenoid that is part of the compressor head is open then you won't get any pressure build up.

I related my experience in previous posts, while troubleshooting my truck it also went down on all 4 corners and made me wonder what I'd done even after replacing part the vehicle would not raise even after driving up to 25 mph, until I cleared the computer. The air ride will not function at all if even one sensor is out range.

Honestly and I can be way wrong here, it seems your just bouncing around on the troubleshooting, you need to start at the beginning so to speak and work through each part. I would jack up the vehicle for easier access, then disconnect the control rod for each sensor and check the voltage on the signal return line while manipulating the sensor, once all that is good, then you might use a probe to provide 12V to the shock solenoids to listen for them to function. Once you've done this you know the inputs to the computer should be correct and the output to turn on the compressor, open/close the vent solenoid, and shock solenoids should be okay. If at that point the compressor runs when it should but the truck doesn't raise then you can probably blame the compressor being worn out
the following is from the manual

Air Suspension Height Sensors
There are two sensors used for the front suspension and one sensor used for the rear suspension. The sensors send a voltage signal to the 4WAS module. The output ranges from approximately 4.50 volts at minimum height (when the vehicle is low or in full jounce) to 0.50 volt at maximum height (when the vehicle is high or in full rebound). The sensors have a usable range of ± 45° compared to total suspension travel of 196 mm (7.84 in) at the front wheels and 240 mm (9.6 in) at the rear wheels. Therefore, the sensors are mounted to the suspension at a point where full suspension travel at the wheel is relative to the travel at the height sensor. The front height sensors are mounted to the frame and the links are attached to the upper arm ball studs. The left and right sensors are not interchangeable. The rear height sensor is mounted to the frame and the link is attached to the rear lower arm ball stud.
When the height sensor indicates that the vehicle is lower than trim under normal driving conditions, the air compressor will turn on and pump compressed air to the system. When the sensor indicates that the vehicle
is raised above trim under normal driving conditions, this will cause the air to be vented from the system to lower the vehicle to its trim height level.

 

Well I don't know exactly all about the measuring voltage. I am basically just trying as people are telling me to try. I do not have the ck suspension light anymore. I removed the battery so I could figure out how to get washer fluid tank out, and when I reinstalled it the light was gone, and wouldn't come back on, but the compressor still won't kick on. So my question is that all of the ride height sensor work alone right? Basically with it low at all corners, if 1 sensor was bad, it wouldn't keep the rest from coming up right?

 

Well I took the air compressor out and hot wire it to run, and there was barely any air coming out. Maybe the strength of blowing out of you mouth onto your hand. And it wasn't coming out of the dryer part either, it was coming out of another part that connects to a big black hose.

 

have you taken it to the dealer and asked them to check it? sorry if you already answered that I don't feel like reading 3 pages again,

at this point it's probably safe to say you have a bad pump, it's alos possible that you have codes in your air suspension module ( 4was) thatis keeping the system for turning on certain codes won't erase until you clear them by running tests with a scan tool. my recomendation is to take it to a dealer, ask them to test the system and before you give them the ok to replace any parts other then the compressor post the codes they gave you and the diag they did,

most good shops can let you talk to the tech and he can walk you through why a part is bad

 

you need to figure out why the pump isn't being told to turn on first before you replace more parts

 

I don't have the ck suspension light anymore. I think it went away when I disconnected the battery to find out how to remove washer tank. I went ahead and ordered the compressor myself, and will install myself since it is way cheaper than dealer qoute. Once I put the new compressor on, if it still doesn't work, I will take it in to get codes read then.

 

How exactly do you jump the compressor relay?

 

I spent less than this to replace my air bag system on my 99 expy.
yes, it would have cost me more than that to fix it.
Front Shocks & valves, compressor, relay...



relay blowing - runs too long
system leaks cause compressor
now requires too many amps
leaking air lines..