I have a 2001 Blazer with 4 button switch. It is stuck in 4WD, I read all the posts about what to check for and everything. When trying to switch to 2WD the TCCM clicks (which I don't know if this is normal or not, never paid attention to it before) and the encoder motor makes a vibration noise for about 5 seconds, then stops for about 15 seconds, then does it again. This makes me think that the encoder motor is bad.

I also think I have something going on at the front end too. I get a humming noise coming from the front which makes me think that the front axle is partially engaged. I disconnected the cable from the diaphram to the front differential and it moves freely when disconnected, but when connected the cable remains pulled and cannot push it in. In other words the diaphram remains squeezed.

 

Is there any way to unjam the shaft that the cable goes to on the front differential? I am pretty sure there should be movement there, but don't want to have to tear it apart. Does anyone have any suggestions?

 

what does the dash switch do when all this happens. when you pres 2HI, does it blink and then 4HI solid light comes back on? or does solid 2HI light come on?

unplug the tccm, that should tell all the elctrical components to switch back into rear wheel drive.

i think humming sound on these trucks is pretty standard, mine makes that same sound even in 2 wheel drive.

 

When I press the 2HI button it blinks, then goes back to 4HI. Just to update on what I have done since I first posted on here. I changed the fluids in the front differential and transfer case just because it needed to be done and to make sure no metal shavings came out, no metal shavings came out, just fluids.

I also took out the front driveshaft that goes from transfer case to front differential to put it in 2WD so I can drive it for now. I still get the humming noise that seems to come from the front. The cable that goes from the vacuum diaphram to the front differential still seems jammed because I still cant manually squeeze the diaphram, its just locked in position. I also took off the encoder motor since it was making ratcheting noise when trying to shift in to 2WD, and I can't get it back on because the shaft for the transfer case and the encoder motor don't match up and can't see to find a solution other than to get a new encoder motor (which I probably need anyways, just wanted to hookup for further diagnostics for now).

I jacked up the driver's side wheel, the wheel spins freely, I jacked up the passenger's side wheel, it spins freely which makes me think that the front differential is not locked in 4WD. I did notice however that the front axles (the shafts that go from Wheel hub to front differential spin when the wheels spin and the driveshafts spinning could be the source of the humming. Are the supposed to spin when it is in 2WD, 4WD, or both?

 

I have a similar problem with my 95 jimmy. 4.3l 4x4. i traded my Suburban for it and i regret it but gas is too much. when i got the truck i was able to drive it for a week before it started stalling. at one point it accelerated and decelerated all on its own w/o my foot anywhere near the gas. i took it to a shop and was charged 300 dollars for a shifter cable and was told the stalling was inconclusive. took it home and the next day it stalled. this time the engine light came on, took it to auto zone and the code was the EGR Valve. well i never replaced it but the light went off on its own the very next time it stalled and thats when i noticed white smoke out the exhaust with alot of condensation so i poured in a bottle of dry gas. the white smoke disappeared but now im stuck in 4wd hi, the switches dont work at all they were disconnected before i got it. so my question is can the 4wd unit cause my truck to stall so much? and also how do i disconnect the 4wd completely so that i can have 2wd hi? can i just remove the front drive shaft? my ball joint and cv axle on the passenger side is giving me problems and i want to save it til i can get the money to replace those but feel the 4WD is gonna kill it sooner then it should.

 

The engine stalling and the white smoke seem unrelated to the issue you have of being stuck in 4WD. As for your 4WD issue hopefully someone else can provide information to assist with the 4WD issue.

 

well i solved my own issue and scored a 1995 Chevy Blazer thats been sitting for quite a few years for 500. its in better shape then my Jimmy and everything is the same, so im gonna use my truck as a parts truck to get this other one running again. will let you know how i make out when its finished.

 

Update: since I took the encoder motor off, now I can't get it back on, the small shaft on the transfer case doesn't line up with the encoder motor. Is the shaft on the transfer case that the motor connectes to supposed to turn about 1/4 turn, then spring back? I can't get either one to match up.