4x4 problems

99 Blazer 2dr.
Just recently I started having trouble with my 4wd. When I put it into 4hi the light doesn't come on saying that it is engaged and when I start driving it feels like it is in 4lo. If I push the button back to 2wd it doesn't disengage directly. It takes about 100ft and then jumps out of 4wd. Does anyone have any ideas of what it could be.

Travis

*bunp with more information

If stopped in neutral or park it will go into 4wd and the light will go to 4hi. When I begin to drive the truck sounds like when the frnt wheel hub assembly is going bad and it drives like when in 4lo. It actually seems like there is more torque. It takes about 100ft or going in reverse to get it out of 4wd.
If I am driving and I try to put it in 4wd the 4hi light flashes about 5 times then it goes back to 2wd.

Any help would be greatly appreciated!

Take the neg battery cable off and leave it off for about 10 min. This should reset the VCM. If this helps then I would check for a bad wire connector near the transfer case or any wires going to it.

I had your problem last winter and reseting the computer would work for at least until the second time I engaged the 4x4. I haven't had a problem since last winter, thus I think moisture is getting into one of the wire connectors. Although, I haven't driven in the rain and tried the 4x4 to test my theory.

Depends if 3 button NP233 case or 4 button 236 case. 4 button 236 case has the vac solenoid on the firewall and they often start leaking internally by now so $45 at the dealer and usually solves the front actuator engagement problem. Also look at all vac lines from the intake by the PCV to the drivers side res and then Ts to that solenoid. The 3 button 233 case has a 3 port vac switch on the side of the transfer case and thats the common failure on those at $15 at all stores.

Mine is 3 button. I am going to check vac switch and vac lines and go from there. Today I searched for the vac switch by the transfer case and couldn't find it? Can you say exactly where it is?

bump

The vacuum switch is on top of the transfer case above the front driveshaft yoke. It will have three vacuum lines connected that are molded into one connector with an index pin to keep you from connecting it wrong.

If you buy a new one, get the o-ring also. Mine didn't have the o-ring and I had to use the old one.

One line is vacuum coming from the firewall neat the brake booster, one is the vent that releases vacuum on returning to 2wd, and one goes to the vacuum actuator beneath the battery box.

Below the battery box the actuator (a cheap diaphram contraption) pulls the cable that goes to the front differential and engages the axle.

My opinion only, your problem sounds like a bad cable or the actuator beneath the battery.
James

I replaced the vacuum switch on the transfer case. I believe the old one was bad as it was stuck up in the switch, however after putting the new on one I still have the same problem shifting into 4hi. It shifted on the fly 1 time at about 15mph at it still felt like it was in 4lo. I don't think that it is engaging all of the the way. When I hit 2hi it doesn't return to 2hi until I go into reverse.
I was going to take a look at the actuator but I found out that my positive battery cable is fused to my battery post. So I am going to have to change cable and battery. I think I will wait until next weekend. Thank you for you help and if there are any other ideas please let me know.

1st Check vac actuator under battery tray for tears, or leaks, and that the vac hose is connected. Replace if found

2nd Check vac hose leading from vac actuator to vac switch on transfer case for cracks and dry rot. Replace if found.

3rd Check remaining 2 hoses from vac switch on transfer case for dryrot or cracks Replace if found.

If all of the above are fine, disconnect your negative battery cable for 1/2 hour then reconnect it. If your 4x4 works after that you probably have a failing TCCM (Transfer case control module)

If that doesn't solve it, it's most likely the encoder motor