...to me once was the air manifold started sticking and you would hear a reptitive air cyling until it time out and error messaged, Are you getting that sound...or not even getting to that point in the tool change? Then I would think mayde it was the carrosel extended position switch (prox. sensor?) or a wire loose at the switch connection. I'm not using the proper names for these parts as I'm not where I can access the manual. I'm just pulling this off the top of my head. Also something has to tell the machine that the draw bar is released. I not sure of all the methods used without that manual in front of me.