recently I noticed that on my 2000 Chevy blazer zr2, that my 4wd was not engaging. I checked the diaphram under the battery and found it to be worn and cracked. so I replaced that, I also replaced the vacuum switch located above the transfer case. after doing that, the 4Wd worked. I used it during the next snow storm. but after that, I noticed that the 4wd no longer engages.
when I hit the 4wd hi, the lights for both hi and low blink, but then it goes back to 2 wd. I do not hear any noise from the transfer case. but when I hit 4wd lo, the lights blink, I hear the transfer case engaging, but then all the lights go off.


I already replaced the 3 button switch on the dashboard and that did not correct the problem.


any ideas? could the vaccum switch had gone bad after one use... but, like I said, I do hear the transfer case engaging when I select 4wd lo. although the 4wd lo light does not come on.

 

That vacuum switch is one part of the front axle engagement system and wouldn't affect your transfer case modes. Sounds like it could be the encoder motor on the transfer case or a TCCM issue. Since the TCCM on my '96 is diff than yours maybe you can get some info here:

https://blazerforum.com/forum/2nd-ge...roblems-85031/

 

It definitely has me puzzeled. After replacing the disaphram and the vaccum switch that is mounted on top of the transfer case, the 4wd worked fine, used it in the snow storm a few days later and 4wd hi engaged and worked oike a charm. that was a couple weeks ago. I tried to engage it the other day and both the 4wd hi & lo lights blink on and off and then the 2wd lite comes on. when i hit 4wd lo, i can hear something engaging in the transfer case, but none of the lites are on. I cant imagine that the vaccum switch went bad after one use...

 

Lube the actuator cable.