I’ve been having troubles with my 2006 Nissan sentra 1.8L automatic transmission, and it’s going into limp mode as soon as I get it down the street so we tried putting new transmission fluid in it (I’m not sure if we drained that much we only put a gallon back in) and it drove two hours away and back and didn’t start having issues until later that night and it threw up codes P0732 I believe 2 gear incorrect ratio. And I’ve just been stuck on what I should do.
Bring it to a transmission specialist
You could check electrical connections going into the transmission for corrosion or damage, but if not that and the fluid is OK chances are the transmission is shot. It looks like that car has a conventional 4-speed automatic rather than a CVT though so it's always possible it's something repairable like a hinky shift solenoid.
As has already been mentioned you should really have a transmission specialist diagnose the problem using a fancy scan tool to see what's going on.
https://www.carparts.com/blog/p0732-code-gear-2-incorrect-ratio/
