Ok I have read all the tec stuff on the site.

I have a 1999 Jimmy SLS.

When I click Auto 4wd the light blinks while I am driving and after 5 minutes goes back to 2. If I click the 4 Hi (When in neutral) the 4 HI blinks for ever until I put it back in 2. The same in 4 LO. I can here the shifting of the transfer case like I always have.

first observation I made was the vacuum actuator is pulling the cable when the 4 hi button or low is pressed. I have looked underneath the truck and the cable looks good.

I grounded pin 13 and no lights blinked to give me any codes.

What else should do now.

Also how can I check to see if the front axel is engaged. A friend suggested chaining to a tree engaged 4x4 and see if the front and rear tires leave a skid mark.

 

Ok I checked the cable comming from the Vacuum actuator cable going to the front axel. There was a plug like connector there as well. This plug appeared to be not connected I pulled it out with no effort so I snapped it back in now it is secured.

That was the problem it's fixed.