Did you start the bike? if not id does show error when reading the codes, same on my, the servo works fine but i get a code with only ign on, probably due to the fact that it does not actuate when engine off so computer does not get a signal from it. Check under servicefunctions and i think you can make it move for functioncheck without engine on.
Exhaustpop with an acra and qs, if you only get 1 pop, you're not opening the throttle enough...it should pop and spit flames on all shifts, no danger. The flap is just there to reduce noise and is more closed the less throttle is open, an adjustable DB-killer so to speak. If you disconnect the wire to the flap it stays in full open position, disconnect the servo and it stays in closed and bike would not run on higher rpm's.