Ok, So after all this "stuff", I reflected back and I'm pretty sure I got myself turned around and made some assumptions about what fits what based on bad data and bad conclusions.

I did take the Bravada out yesterday for a little mild mudding to see if things were properly working or not. I didn't go crazy because it's out in the middle of nowhere and my tires aren't the best. It performed awesome. And I also found out, using the RPO codes---something I didn't know anything about--- that I have a g80 rear and 3.73 gears. I'm happy about that.

It was the computer (TCCM) after all. My original Encoder works just fine. Transfer case is great. In the end I learned a bunch of stuff.. even if it cost me a couple hundred bucks. Thanks to everyone who tried to get me straightened out.

 

Congrats! And thanks for reporting back. These final reports are super helpful to those who have a similar problem in the future.

 

I know this is an old thread but I’m having the same issues. I also have a 98 Bravada that has an orange plug on the TCCM too. The only TCCM I can find are the green plug that doesn’t fit. So the TCCM you got to replace was out of an Astro van? Do you remember what year by chance?

 

It's been awhile. It was the similar year astros. They had the same exact drivetrain. Make sure it's the smart trak version. Check these part no.'s... no guarantee. 12577413,15748744, 15011608 With those you should get enough info to find all the part numbers that fit this application.

maybe this one.. Prices have gone crazy.
05 CHEVROLET ASTRO Transfer Case MODULE 12577413 | eBay

 

For my 1999 Blazer ( the 4WD does not work right all lights are out) and it is TCCM is 15154323 .I got a used TCCM #12577412. but the 4WD does not engage and just blinks .Is this 12577412 TCCM compatible for my Blazer? Will I have to get a TCCM 15154323 same as the original ? Can I program this used 12577412 TCCM? Any comments would be helpful. The used TCCM I bought has the same plugs for connecting.

 

Either of these TCCMs should work fine in your 1999 Blazer with NP8. No programming required.

Probably you have something else bad like a shorted encoder motor that may or may not have ruined your original TCCM. This is what happened to mine back in 2015. I had to put in both TCCM and encoder motor, in order to get things to work.

These 4WD systems are a piece of cake to work on if you have the Tech 2 factory scanner or one that will do the same things with the 4WD. But actually quite difficult to diagnose otherwise.

The simplest way to diagnose without the proper scanner is to first check wiring/connections on TCCM for corrosion and fuses (several fuses involved in 4WD see attachment), then bypass (vacuum) on the front axle solenoid and make sure axle will mechanically lock in the RF wheel (jack the RF wheel off the ground and physically feel the difference when turning locked in/not locked in). If those are OK, then take off the encoder motor and make sure you can move the transfer case through its range with a wrench. If that is OK and you don't want to pay the diagnosis fee at a dealer, put a (Chinese) Amazon encoder motor on it (DO NOT just plug it in - that will ruin it. Must be installed). If still doesn't work, then replace the TCCM with a Cardone 7342102.... currently $134 + $80 core at Rock Auto. My Chinese encoder from 2015 is still working. Good luck

https://blazerforum.com/forum/2nd-ge...-blazer-89044/