I hope this is in the right place if it isn't, sorry! But I really need assistance with my Blazer. I have a '02 Chevy Blazer with 4 push button 4wd. It is stuck in 4wd, I don't even know if it is 4hi, lo, or anything. My dashboard says to service the 4wd, the lights on the buttons aren't on, they flash when the car starts for an instance so I can't engage it to switch it from where it is stuck. Here are the the things that I have checked, and rechecked:
Fuses, vacuum actuator, vacuum lines, solenoid that connects to the vacuum lines, transfer case, I cleaned a little bit of corrosion off of the contacts but it did nothing. Is there any way to check if the transfer case is actually working? Also if I try and convert the truck into manual 4wd will it make my computer go all squirrly? Any help with troubleshooting this will be greatly appreciated, is guzzling gas and makes a loud warbling noise.

 

Remove the vacuum line going to the vac switch that comes from the driver side of the truck and plug it with a 3" nail. This will make sure your front diff is unlocked.

You'll know if your in 4Low if the truck revs right up an goes no where fast. If you figure your stuck in 4 high you can always remove the drive shaft for now.

I'm faced with the same problem right now and figure its the encoder motor even tho its only 1 1/2 years old. I swapped out the tccm and no change.

 

I already unplugged the vacuum lines and plugged them and it was a little funny because the car started right up, actually better than with the vacuum lines connected. . I don't know if this is useful in diagnosing the problem but when i put the car in neutral i was not able to rotate the front drive shaft. I was going to remove it for the time being but because i could not rotate it it made it increasingly difficult to get to the bolts. (I don't really have much equipment to actually lift the vehicle off the ground to be helpful.) I don't remember what the name of the part but it is the cable that goes to the vacuum actuator. I checked that and though it was a bit rough in the housing it was also fine. Thanks for your suggestion!