Kelsmorr

I have a dewalt 20v impact driver (DCF885) that began to work intermittently. Upon taking the tool apart, I found that the cause of the problem was a wire became disconnected from the battery contacts so I soldered the wire back on. After putting the driver back together, the tool works fine, but the "auto stop" function stopped working (the drill just spins to a stop instead of stopping to spin as soon as the trigger is released). Any ideas what could be causing this, or what mechanism is responsible for this function?? Thanks in advance.