[Dukesboy101]

I have a 2001 Nissan Frontier SC and it has 4wd that doesn’t want to engage. Before this happened it used to make a bad grinding noise, but the 4wd still engaged. Now it doesn’t make that noise but the truck is stuck in 2wd. We have replaced the front hubs and CV axels to no luck. Think it’s an actuator somewhere but don’t know where it would be located on the truck.

 

[RedDR]

There's no actuator other than your arm.

You'll need to get up under the truck and inspect the transfer case linkage. Unless you find something whacked there, you'll probably need to drop the transfer case and open it up.