Exhaust brake isn't working.

I recently purchased a 2005, Kodiak, C5500, Motor-Home, Duramax, Allison. The MH is equipped with an air operated factory GM exhaust brake. There is small compressor and air tank under the truck below the driver's seat. There is an electric sending unit on the bottom of the air tank that I think shuts the compressor on and off as needed. There is also an electric toggle switch on the dash that controls the brake (on/off). Additionally, there is an electric solenoid in the air line that activates the butterfly valve/exhaust brake.

The butterfly exhaust valve was frozen when I purchased the MH but I was able to free it up with a lot of wd-40. I am going to replace the compressor with a good aftermarket unit because it makes more noise than air.

The bottom line is that when I connect the air tank to my shop air supply and turn on the exhaust brake it does not work. I am not sure how to trouble shoot this. Does the computer not let the system function because the truck is stationary. Any help on how to trouble shoot the EB system will be appreciated.

Thanks
John

The exhaust break system, like nearly every other "OEM" type, (including class 8 trucks/tractors), the break circuit is a collapsible series. Meaning, any number of incorrect conditions will prevent it from engaging. Sitting stationary is one of them. Electronically controlled modern systems require zero fuel input. You'll have to duplicate the correct operating conditions to "test" it, such as actually driving up to a minimum speed, then decelerating.