My exhaust brake on my topkick GMC diesel just quit working.
the button on the dash has a light on it that will come on when the exhaust brake is engaged but it isn't working anymore. No light and no exhaust brake. Can't find a fuse anywhere for it and the air line is good. Cylinder is not froze up. Cruise control is not on.Any other ideas?

Just a suggestion ... Seems like an electrical problem. Start tracing the circuit from your cab control to the solenoid that actually moves the valve.