Hello,
Michael has the right answer, If the motor is not working than it will not go into 4WD but you can remove that motor and actavate it off and see if it is working
The transfer case has a stepper motor on it to switch between 4wd and 2wd. Those are common to go bad. If the module sends the command to switch to 4x4 and the motor does not move all lights will go off and it will stay in 2wd. I've replaced several and it solves the problem 98% if the time. The motor varies on the model of transfer case and also on if you have a 3 button control or 4 button. It will bolt to the side of the transfer case
The 99 blazers have a problem with the 4wd transfer case module. The module is located inside on the passenger compartment, right side front behind the "A" pillar kick panel. Make sure the connections are dry and doesn't look like water has been leaking on it. make sure the connections are not corroded and locked properly. If all looks good and the 4wd module is not blown, replace the module. The module runs about $150 to $200 depending on whether its a 1 or 2 connector reconditioned module or you can check the salvage yards.
Good luck.
You replaced everything. The only thing left to fix would be the wiring. Check for power and grounds first. then start replacing the wires.
Sometimes this works, sometimes it doesn't. The other day someone told me the vacuum actuator is located under the battery. As soon as I removed the battery bracket, battery still connected, The switch worked and the 4h/4l worked, I tightened up the battery bracket and all of a sudden it stopped working again.
I repeated the above steps and everything is working properly for now! Any ideas as to what might be causing this?
Thank You...
A. I'll try to explain how this system works for you. When you push a button, the signal goes to the Transfer Case Control Module (TCCM), a small metal box under the dash. In turn, it sends a command to the encoder motor which is mounted on the side of transfer case.
On a working unit, the transfer case will shift to the selected range. This will cause an internal movement of the linkage which pushes up on the ball of the vacuum switch. The vacuum switch has 3 hoses to it. One is the supply from manifold vacuum, one is the feed that goes to the actuator under the battery. The other is to drain off the vacuum when it's taken out of 4x4.
There should be DTC's stored if you can't get it to shift. These are read by jumping 2 wires in the ALDL plug under dash. All codes will have you check for 5 volts at the encoder motor plug on the 4 terminals. I have had this trouble in the past and fixed a few by running a new ground wire to the encoder terminal that is ground. I don't have a schematic handy so I can't help you there.
Unplug the TCCM, try tapping on the encoder motor and re-install the plug after it's been unplugged for at least 2 minutes. Cycle the ignition on and off 5 times, then on. Now try to make a shift.
I have seen ruptured servos under the battery. Battery acid leaking down and eating into the servo cable that runs to the front axle making it too stiff to move the cable. If the switch light changes from 2 to 4h, the TCCM and encoder should be okay and the problem is most likely in the vacuum switch or servo area.
This is all I've got.Hope this helps?
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