Car randomly stopped shifting properly one day. Never hard shifted or missed a gear once. Car will shift 1-4 and then it stays in 4th gear until you put the vehicle in park and turn it off. Throws one code. U1000. CAN communication issue... Everything I'm reading points to the ECM/PCM. I had computer problems with it before. On really hot days the computer would overheat and cause all the lights on my dash to come on and none of the electronics would work. Car would go into limp mode. Thinking I can order a new one already programmed to my VIN and it'll fix my issue, but Idk. Any advice?

 

I drug pretty bad in a driveway one day and it stopped shifting after that. Makes me wonder if i damaged the valve body, or broke or disconnected a wire.

 

I'd start with a visual inspection under the car for anything obvoous, verify you have the transmission harness that connects into the tranny with a single large plug and not the one with the 2 green 1 black plugs on the side of the transmission.

 

what’s the difference if I may ask

 

Difference is one has an accessible TCM and one it's inside the transmission. U1000 just means SOME computer is disconnected but it can be tricky to find out which one without the dealership Consult - II / III tool.