Front end wont engage even though it will go from high range ito low range

2 speed electric shift transfer case problems #1 jack up truck place on 4 jack stands. Start and select 4 high position in drive release brake ad watch front driveshaft does it turn "yes" problem is axle actuator on passenger side of differential not engaging axle shaft. "no" apply brakes bring to a stop engage low range does low range work "yes" internal transfer case problems "no" electric transfer case shifting motor failure.

You will probably need a shop manual to work on it yourself. The switch on the dash controls a vac servo on the transfer case. The servo controls an actuator under the battery which sends vac to the front axle. The transfer case and front axle servo work together.

Could be the servo on the front diff not activating. Could be a power prob or failed unit.

The transfer case is stuck in the low range. If manual shift try shifting from low to high several times to see if free up. If electronic, check all fuses and make sure you hear transfer case change range. Do this by shifting with key on engine off. If no change refer to qualified transmission mechanic.

Most likely the button the dash is shot. I had a Blazer that did the same thing. Took the button apart,cleaned it and started working fine.[contact was bad]....just a thought before you go out and buy one !!

after looking at the schematics for this vehicle, I can say with great certainty that you might have something wrong in your front axle on a straight axle model that wont let the servo engage the front axle. Now if you have independant front suspension, then where the servo motor goes into the transfer case could be the problem. pull the servo motor from the case/axle and look at the engaging mechanism. You are looking for worn parts that could cause binding or broken parts. This servo motor gets its command voltage from the ecm. The signal for the ecm generates from the transmission and your in cab switch. If you can hear the motor trying to engage, then all the other factors are working up to the motor arm. The light is just a by product of the ecm trying to engage the front axle

the front axle bearing could be shot. This is common. Also the hubs may not be locking which is even more common

the motor on the back of the transfer case may be stuck knock on the motor lightly with a hammer when switching the the switch May need a motor

I am going to assume that you have auto 4x4, and not manual shift base model.. it just sounds like the servo motor that shifts between 2x4 and 4x4, has gone bad

question:
does it still engage into low range, even though it is stuck in 2x4?

I had a very similar problem with my 98 gmc 2500. The 4 low would engage - though the upshifts were erratic, but no 4 high though the light sometimes came on. I changed out the electric shift solenoid or whatever it is called, on the transfer case and it worked fine after that. A fairly simple fix that can be done in 15 minutes. Hope this helps.