Try this brochure from Detroit.
Aux. Output #3 Open Circuit (High Side) - S3 whitch is sensor out put.
i hope this helps
My name isXXXXX will try to help you out, DDEC 3 code 25 actualy means there is no active or inactive codes, no trouble shooting needed. Code 31 means the engine brake low or medium circuit has a open or is shorted to ground, there are a whole list of things to check, but in short, check wiring, comming up and behind the engine going up to the head for rubbed wires, Also a common area for this would be a diconnected wire to one of the jake solinoids under the valve cover, they just use spades, I have found this a few times... By the way if you dont have engine braks, the engine is configured for them and it shouldnt be , this will take a dealer data change... hope this helps