4-wheel high not working!

i have a 99' gmc suburban with four wheel drive. my 4wheel low works fine, but if i try to go into 4 wheel high the light lights up but it doesnt engage and i end up with just staying in two wheel...any suggestions?

i had the same problem almost exactly...you might want to take a closer look at your 4-lo. i thought mine was working too because it was geared lower but the front tires still wouldn't spin. its probably your 4x4 ACTUATOR...i replaced mine for $110 at the dealership and it worked fine...it only takes a couple minutes to install (unplug one wire and unscrew the actuator...then screw the new one back in and plug it in) its a cylinder that sticks out of your front differential and its about 2 inches in diameter and maybe 4 inches long...good luck