Why wont my 2008boy altima shift up or down when transmission gets warm?

this means that the cvt belts is worn out and its not griping the cones in the transmission follow the above dudes answer go to the dealership and get a new belt fitted in it !

hi so today my 2009 nissan altima sedan while i was driving on the freeway my car wouldnt shift down when trying to accelerate but no check engine light came on i exited the freeway and came to a complete stop and when i took of it did the same thing it felt like their was no power but the gears where going in i went to a gas station and turned the car of for about 5 minutes then took of and it ran normal again this is the first time this has happened to me need help please

I had a similar issue in my 2012 altima 2.5. My symptoms were that when it was hot (90+), on the highway I would find myself stuck in 6th gear and unable to shift down or up. The car would shift with a change in speed, but barely enough to get off the highway to park (ie, it was always 1 gear or so above where it would have normally been). Stopping and turning the car off might fix for a little while. I took it to the dealership and they said the problem was that the transmission fluid was overfilled by as much as 2 qt. I've never done it or had it done, but Firestone (who does my oil changes) must have "topped it off" for me. Luckily they used the correct fluid or I would have really been screwed. This may be only one of many causes, and I don't know how to correctly gauge if its overfilled or how to resolve it, but that was what the dealership found. I recommend taking it to a dealership to get checked out over doing it yourself but its one possibility.

Hey i have a 2008 nissan altima had since 2014 i been driving my car nevef had a problem until i hear it kinda not wanna switch out so i took to get tested by oreilly they say i got sensors on my transmission up and down switch and and that why slowing up not speeding do u think it will be high and i am so hurt but i no God will make a way for me pay it and he told me go let Petro check it but i just got oi lchange two weeks ago they didnt say nothing please help

For no reading fail code case, the CVS fluid might be low or overfilled. However, the transmission temp sensor could register an overtemp limit; therefore, make sure that the radiator coolant system does its share in cooling the CVS fluid line (50/50 mixing if using concentrated coolant).

I have the same problem when climbing mountain grades over an extended time. I believe the CVT transmission gets too hot and or pressure rises.. This results in my transmission locking in 6th gear - unable to manually shift up or down or put in neutral. It has reverted back to full operation after cooling down. I have a brand new radiator and thermostat. I dont think the trans cooler is large enough.