all of a sudden when my wift went to use the passenger side seast belt it wont unlock at all. does any one have any clues to solve this or am i looking to have to buy a new seat belt unit????

I've never torn apart a seat belt, but I would bet they are simple machines.

I have never liked how easily the Xterra seat belts lock up anyway.

The seat belt buckles operate as a spring loaded latch the button slides down and wedges the spring back allowing the tounge to slide out.

a lot of times something like a coin gets behind the spring stopping it from going back.

If you have some feeler gauges like a 0.18 to a 0.24 you can slide one down into the reciever/buckle in between the tounge and the red buckle button it will let the buckle release.

Then look inside for Debris /coin stopping the latch from going back freely
fish out the debris or unbolt it and shake it upside down to get it out.
Then if it is still sticking then you will only need the buckle/ reciver replaced and not the whole seat belt.

It has worked for me before
hope this helps

I am not entirely sure what you mean by the seatbelt will not unlock when you go to use it. Is your problem that the seatbelt will not pull out from its base so you can bring it around to the buckle? I had this happen to me. If that is your problem ----

DO NOT MESS WITH IT.

The seatbelts come with a very long warranty -- on my 2002 it is a lifetime warranty. On more recent models, I believe it is 10 years. If you mess with it, you may void the warranty.

Also, the front seat belts have an explosive pre-tensioning charge. If you accidentally set it off, you will have most likely have to pay for a new one.

Just go to the dealer.