I have a 97 blazer, 5 speed. My ? is do I need a scan tool to figure out whats up with my 4wd. The 4hi is on but the front isn't locked in,and it will not switch back to 2hi.

 

Well, most code readers won't read anything but the generic P0 codes. It all depends on if the 4wd even has fault codes that set in the PCM... Most of the time, transmission and drivetrain codes are not readable on even some manufacturer specific readers. It would probably end up being a chassis code or 'C' something.

I'll let some others on here that have dealt with this issue before comment, but please elaborate on what is going on with your 4wd and what led up to this happening.

 

when I got the vehical the 4wd worked fine then the last time I went to use it the 4wd kicked in and worked then when I went to go back to 2hi everything seemed to be fine. on down the road my 4hi light come on. crawled under itand the front driveshaft spins like it is in 2hi, with the truck in gear.