I just got a Supercharged H2 that was lowered a little, and was permanently giving out the Service Air Suspension Error.
I went to a shop to have it raised to stock height, and what they did to lower it was weld something to the shocks to make it go down a little, I had them re-weld it to the original state, and they also put a little thing under each of the Air Suspension Sensors, they had something under it about 1" long, I had them remove it and screw it to the original place. I don't know if the car is exactly at the same measurements as the original, but it was now raised 2" total, and seems about right.
So this work was done, and the car is still giving out the same error. I tried resetting the battery, but it didn't help.

Any sugestions?

PS: Compressor is working fine, air bags are not leaking, the car suspension was never down, so it should be a sensor/programing error. Going to a GM dealer is not possible because there is none in my country.

 

I would look in the passenger rear wheel area. There is a level indicating mechanism. It's a rod with a plate that moves with the vehicle load. Make sure the target is being read by the sensor. Any pics would help of your setup and lastly, check for leaks with soapy water in a spray bottle.
I am not an expert so take my suggestions with a grain of salt.

 

I will take some pictures, later today.
About spraying with soapy water, like I said there are no leaks, there is no problem with the air ride, it never sags, the problem is that they lowered it and messed up the sensor readings or something.