When I push the buttons it’ll go to 4lo light comes and I hear a clunk but the 4x4 doesn’t engage. When I press 4hi the light doesn’t come in or it goes to 4lo what could be my problem? Or where should I start my diagnosis

 

To get help you'll have to provide the following the year of the Blazer and if it has the 3-button or 4-button 4wd system. The 4-button 4wd system was introduced in the late 90's (98?) and has an option for Auto-4wd in addition to 2Hi, 4Hi, and 4Lo. Also describe for people if 4Hi high works and how you determined if 4Hi works? I.e. can you tell the front axle is engaged or not? If in 4Lo does the truck act as if it is in 2Lo (which should not happen but would if the front axle is not engaged). Finally, do you hear any clicking from behind the right front kick-panel in the passenger compartment. (This is where the transfer case control module is located)

As for failure mechanisms, these include the transfer case control module (TCCM), the 4wd selector switch, the vacuum that engages the front axle, and a solenoid on the transfer case. (Have I missed anything folks?) Look up threads for diagnosing 4wd problems with reference to these issues and you can better help diagnose what is wrong which will help people at the forum get you to a solution even faster.

 

2000 Blazer 2 door ZR2. I have the 3 button 2hi, 4hi, 4lo. Yes the truck acts like it’s in 4lo. Messing with it I put the tcase in 4lo and the drive shaft is locked (in park) and in 2hi I am able to spin the drive shaft freely.

 

So by what I’m experiencing I should look towards vacuum problems and not the motor?

 

If your front driveshaft is locking but still no 4WD then the transfer case is working but the front axle is not locking in. There is an actuator underneath the battery tray that engages the front axle. On your vehicle it is operated by a vacuum switch mounted on your transfer case.

Just start the engine, put it in 4WD (trans in park), and jack up the right front wheel off the ground. If the 4WD lo or 4WD hi indicator is illuminated steady, yet you can spin the RF wheel with your hands (front driveshaft does not turn) - then the front axle is definitely not locking in. Begin by figuring this out and report.

 

Correct me if I'm wrong but doesn't the 2000 have a electric vacuum valve on the firewall instead of the older style transfer case switch

 

I'm pretty sure it is only the 4-button systems that have the electrical vacuum valve that hangs from the top, center of the firewall.

 

You maybe right - When I posted I had looked up a 2000 Blazer up at Rockauto and all they show is the electric switch ....