I just changed my transmission in my 2008 Altima and these are the codes that's coming up p1777, p0740, p0745, p0778, p1740, and p0125.
Except for the P0125, everything listed has to do with electrical problems with the transmission. It would seem to me, there are several things which could be at fault here:
- You have not properly connected the wiring harness to the transmission. You can try reseating it to see if it will work. Did you even plug it in?
- You have damaged the wiring harness connector or wiring in the process of the transmission change. You can pull the connector and see if any pins are bent on either side (I don't know whether the transmission has the pins or the connector does.) Also inspect the wiring to ensure there's no breaks or frays.
- You have got the wrong transmission. You'd have to double check the transmission code to see if it will actually work in your car. You might have to check with Nissan to see.
Beyond that, you might want to check your grounds to ensure they are connected properly. Everytime you try something, ensure you clear your codes so you are starting with fresh information.