PCM/Transmission, transmission does not shift properly?

Vehicle starts and runs perfectly well. However, transmission does not shift properly. It started very suddenly at the snap of a finger. However, it does still shift and can be driven. But when I try to hook my scanner tool to it, it no longer reads anything. In fact, it doesn't even light up, as though there is no power coming from the Module. I was assuming it was a PCM issue. But I am unsure. The only light on the dash is a service engine soon light. It doesn't seem to be a transmission issue because if it slips out gear, turning the engine off and back on solves the problem and will go back into gear again. Any ideas would be great. Thank you!