4x4 not locking in, here it engage but not lock in

It sounds like the front diff accuator may not be working. The 4wd control module will store fault codes which you can read with a scan tool. The fault codes should lead to the cause of your problem.

this problem is common . there is a vaccum hose that goes from under the battery tray to the back of the engine. make sure this hose is connected and not cracked or broke or weak, that was the problem with mine, had to replace 8 foot of vaccum line to fix several problems, ex. 4x4 locking in, cruise control working, heater switching from defrost to floor. etc.. hope this helps