No 4WD - Help, it's snowing in Denver!
 

I have read numerous posts regarding 4WD not working in these Blazers, but none that seem to address my specific problem - namely...
1. RF axle constantly engaged.
2. Constant vacuum to the actuator under the battery.
3. The transfer case not engaging the front drive shaft.
I appreciate any suggestions anybody has.
I have a 2002 Blazer, Automatic Transmission, with the 2H, 4H and 4L pushbutton switch on the dashboard (no Automatic 4WD). I have done some diagnostics, and here is what I have found:
The vacuum actuator under the battery holds vacuum. Vacuum to this actuator is constant, regardless of which of the shift select buttons is pushed and lit. Therefore, the right front wheel is constantly engaged. However, the transfer case is not engaging the drive shaft.
I have checked all relevant fuses - Crank, ATC and 4WD, and they all are OK. The wires to the TCCM behind the right kick panel of the front passenger seem to have no corrosion. I have attempted grounding pin 13 on the data link cable and I get no flashing lights on the shift select buttons when I turn the ignition to “on”. All of the lights on the shift select buttons come on briefly, then the 4H and 4L buttons go off and the 2H button stays lit, indicating I am in 2H, which is correct.
A few posters have instructed to pull the 5 amp TCCM fuse at the bottom of the fuse box, but I cannot find any such fuse on my vehicle. I pulled the other relevant fuses for over ½ hour and even disconnected the battery, then turned the ignition on 6 times to clear any codes. I also tried the instructions in the Blazer owner’s manual detailing to shift to 4L and put it into Park while the 4L light is still flashing to no avail.
I hear the transfer case clunks when I shift from one mode to another, telling me that the transfer case is shifting when I push the buttons to 4H or 4L, and the lights blink momentarily, then remain lit on the button I have selected. 4L does engage in low gear, but I still have no power to the front driveshaft.
Any ideas?
Thanks in advance!

So the lights do light up indicating that the TCCM thinks the transfer case has completed the shift, however, there is no power being sent to the front axle?

If there is always vacuum to the front axle, the vacuum switch on the transfer case has froze up in the 'on' position and needs to be replaced. Autozone & Advance Auto both sell the dorman part for ~$15.

If the front axle is not being sent power at all and the front axle itself is properly engaged, then there likely is a problem inside the transfer case.

The ball in the vacuum switch on the t-case could be stuck.

Correct, the lights do light up indicating that the TCCM thinks the transfer has completed the shift. As a matter of fact, I hear and feel the telltale “thunk” indicating stuff in the transfer case is shifting.

I am going out to pull the vacuum switch on the transfer case to try to replace tonight, however, your comments about a problem inside the transfer case are disturbing. That doesn't sound cheap or easy.

I had read somewhere about spraying WD40 on the electrical module that plugs into the transfer case, and something also about moving a rod on the transfer case to free it up. What are your recommendations on those operations?

Can that ball be easily unstuck, or is it best to simply replace it?

Just replace the vacuum switch.

If the transfer case is indeed slipping or, worse, not sending any power to the front axle at all even though the TCCM states that it has completed the shift, there is a problem inside...

OK, I am off to get the vacuum switch. It seems you don’t think that will fix the issue, but at least that front axle may disengage, saving some gas.

Is it even worth looking at the electrical switch? No point trying to move the shift rod?

Sorry about the consecutive posts. I didn’t take the time to copy and paste both quotes. Thanks for consolidating that.

Sounds like I may or may not be in the same boat you are. I had a similar problem and replaced the switch in the t-case. Front driveshaft disengaged. However I just tried driving up the hill today and had to turn around since 4wd would do nothing.

If the switch is working correctly, I should be able to put the front up in the air, push 4hi, and not be able to rotate the driveshaft if in PARK? I should also be able to rotate one front wheel and the other should turn in the opposite direction if the front is locked in as well?

No need to copy/paste. Use the multi-quote feature (https://blazerforum.com/forum/images...iquote_off.gif) by clicking on the button of each post you wish to quote, then hit the quote button (https://blazerforum.com/forum/images...tons/quote.gif).

Thanks for your help.

I have slept on the disappointing news, and am wondering what you recommend on the best course of action. Fix what I have (??), buy a used transfer case on Ebay ($200-$300)or from a local junkyard(??), or a rebuilt one ($900++)?

It really depends on what is wrong with it and how long you expect to keep the truck.