I recently purchased a 2000 Blazer LS, auto 4wd, which unfortunately seems to be a great truck that has a few issues. I've just finished replacing the encoder motor tonight, thanks 100% to all the great info I found searching this forum, and it's definitely shifting now. So now my theory is the the front axle is not engaging when I shift into 4x4. I can definitely hear the transfer case shift but the 4x4 lights just keep blinking. It doesn't give me any codes to pull, and the 4wd service light has never even come on. I've poured over numerous posts here and it sounds like I have it narrowed down.

I'm not sure if the posts I've read refer to the 4x4 vacuum actuator or the front drive axle vacuum actuator to fix this issue though. http://www.am-autoparts.com/AM/Four-...9/AM-24277122/ or http://www.am-autoparts.com/AM/Four-...3/AM-36913506/ are the two I'm looking at. Just at the point where I don't want to pick the wrong one.

 

To pull codes from the Auto4wd (NV236) transfer case, you need a scan tool capable of accessing the TCCM. You cannot pull the codes with a generic scan tool nor are there any DIY procedures that work without a full feature scan tool. There likely is a code stored.

Both of those items are for your truck. The first link is for the vacuum solenoid mounted to the firewall. This allows engine vacuum to pull in the vacuum actuator under the battery when 4wd is requested. The solenoid should be energized whenever Auto4wd, 4HI, or 4LO is selected. Once energized, the solenoid opens up and allows the engine to pull a vacuum on the actuator. The actuator needs to be pulled 0.5-0.75" in order to engage the front axle.