Fuso FEC72S AAF0E2

Im at my wits end with this thing. Truck came in for exhaust leak at manifold. Resealed with all new gaskets from mitsubishi. Sets code for engine brake solenoid any time you try to put it into regen. Brake position reads as invalid in my scanner. Replaced brake, same problem. I have full battery voltage and signal in the right places. I don't have OE software. Some mitsubishi guru, please help me