I bought a 2005 dodge ram 1500 4x4 back in maywith 20000 miles on it. when i first bought the truck the posi was working and a couple months ago it just quit working. i took it into the dodge dealership to get it checked out and they told me that my truck never had posi and i know it did. any ideas??

 

Yeah, check the tag on the diff. It will tell you. You can also get a copy of the window sticker from the dealership or online with your vin.

 

It may not have. In the right conditions, it will spin both tires without it.
Read here and submit your vin and ask for a build sheet.
https://dodgeforum.com/forum/3rd-gen-ram-tech/179642-build-sheet.html

Mine came back like this

3.92 Axle Ratio
Corporate 9.25 LD Rear Axle
Anti-Spin Differential Rear Axle



Anti-spin is the limited slip unit.

 

That might not be a bad thing if you have no stock LSD.
Just do a search on the dreaded retaining/c clip problems on these stock Dodge LSD's.
They are a NIGHTMARE!!!!!
If you havent got an LSD installed, consider buying a Detroit Trutrac or an Aurburn LSD.
That way, you will get a bullet proof LSD and not have to worry about the "grenade waiting to go off", that is the stock LSD that Dodge install.
Hope this helps?
Al.