i have a 99 blazer and when you hit the 4hi button you can hear a switch working over by the battery but doesnt engage in 4 wheel and the light just blinks, and when you hit the 4lo button you can hear and feel a clunk of engagement in the front end and it gives you torque like its in 4lo but the front wheels dont engage and i just had the front wheel bearings done. i have no idea what to replace but i have to have 4 wheel i live on a mountain with snow drifts. Even tho its springs my driveway floods and becomes a sink hole for the mud and i can barely get in and out with 2 wheel with cooper discoverers wrapped all the way around it all year round.

 

Transfer case!

 

Maybe these threads will help you...

https://blazerforum.com/forum/2nd-ge...uestion-78644/

https://blazerforum.com/forum/engine...madness-78518/

 

Sounds like the passenger side front axle is not locking in. Without locking in, the transfer case shifts into LO, but no front wheel engagement. How many buttons on the 4WD dash switch, 3 or 4?

Raise just the right front wheel off the ground, engine at idle, trans in neutral or park, select 4WD LO: Is there vacuum at the axle actuator under the battery tray? And, does the wheel rotate by hand?

 

Its the 4 button. It won't do anything in park I have to be in neutral for it to attempt 4 wheel. You can a hear a clink when in goes into 4hi and a clunk when going into 4lo and sometimes it won't let me out of 4lo without rolling slowly in neutral for a couple feet. Ill have to try the tire off the ground. Yes there is an actuator under the battery