I have a 2004 Blazer LS with 3 button 4x4, when i try to engage 4hi it does not engage but when i put it into neutral and engage 4low it engages perfectly fine. But then as i proceed to put it into drive and give it gas it goes for just a second then shifts. i think it tries to go into 4hi but then i just give it gas and nothing happeneds. Does anyone know how to stop the “shift” from occurring and to keep it into 4low?

 

Not quite sure about what your complaint is...

...The 4LO will engage the 4x4 and in addition to that also engage a 1:2 reduction-gearing. That means it halves the output speed (rpm) on your drivetrain.
By doing so it doubles the torque. This means that when you block it in first gear at let's say 2'000 rpm instead of going 25 mph it only goes 12 mph. (yes, I know12.5 mph it it's a 1:2 reduction gear)

One side effect of this when driven in "D" (drive) is that it does shift harsh and at only half the speed you would expect.

This is the write up I've posted a couple years ago on 4x4 driving. Should have all on 2HI 4HI 4LO.

https://blazerforum.com/forum/genera...rmation-88400/

 

Adam12.....now that's an old TV show.......anyways, have you checked/changed the vacuum lines under the hood? Checked the condition of the vacuum actuator under the battery? Does the cable between this actuator and front axle move freely? Check the TCCM connector contacts for corrosion. Might also remove the 4x4 switch from dash, disassemble and reflow the solder on the connector pins.

Have another person in driver's seat, engine running, trans in PARK. Get under Blazer, find the encoder motor, have other person select 4HI and feel/listen for encoder motor movement. If nothing, then could be the 4x4 switch in dash or motor has failed. Also suggest clean the electrical connector for the encoder motor.

Try these things and then come back with what you find/do.

Have fun.