Hey everybody I am having issues with my 4hi. I have looked up what parts usually cause the problem. I have ordered the vacuum switch and the vacuum actuator, but I'm also looking to take care of the encoder motor as well...does anyone know what transfer case is in the 99 Chevy Blazer so I can figure out which encoder motor I need to purchase that will be a direct replacement.

Thanks

 

For a 1999 you would have had one of two options: the "3-button" NVG-233 (RPO: NP1) or the "4-button" NVG-236 (RPO: NP8). The RPO codes are on the sticker on the inside of the glove box door but the easiest way to tell is what sort of 4wd switch you have on the dash: 2Hi, 4Hi, 4Lo Or 2Hi, Auto, 4Hi, 4Lo.

What are the types of problems you are having? Have checked that the vacuum hoses in the engine compartment are not rotted and leaking? I have a thread link in my signature for the vacuum hose replacement.

 

Thank you for the reply. That helps a lot I have the 3 button (NP1). As far as the problems I am having...when I'm in 2hi and in drive and push the button to engage 4hi nothing happens(no sounds of it attempting to engage)...the light will flash and then it will shift back into 2hi. But when I am in neutral and push 4hi you will hear it try to engage but nothing will happen. I go to shift into 4low you will here it engage but both 4low and 4hi lights are on. If I try to go from 4low to 4hi it will either switch to 2hi or back to 4low.

From what I have been able to find it's either the vacuum actuator and switch or the encoder motor. I have found that it could also be the TCCM in the passenger side kick panel inside. But I wanted to start with the least expensive of the parts and work my way to the more expensive.

 

I think you are on the right track. One thing I would suggest that because it is so easy to access, you should at least inspect the TCCM. The terminals will get corrosion. Are you hearing any clicking sounds coming from the behind the passenger kick panel? There are relays that you should hear click once as it gets commands to change mode. One of the ways the TCCMs fail is to start clicking a lot with 4wd not engaging. I was able to get a NOS TCCM off of eBay for a good price when mine went out. I don't know if there is a different one for the 3-button vs. 4-button transfer cases but it would not hurt to check. If you have access to a You-Pull wrecking yard (or even a regular wrecking yard) you might see how much a TCCM from there might be.

 

So yesterday I checked the TCCM and found no apparent corrosion on the female or male ends. However after I had plugged the TCCM back in I attempted the switch to 4hi at which time I heard the click but it didn't switch to 4hi. After getting it back to 2hi I attempted a few more times to switch it into 4hi again and the 4hi light kit up but it didn't sound like it was engaged. I got it back into 2hi and attempted again to switch to 4hi but these times there was no clicking sound. Do you think that it could be the TCCM based off of that happening? I'm waiting for the other parts (vacuum switch, vacuum actuator and encoder motor to come in hopefully sometime next week.

 

That it clicked once and then did not do it again could mean that the TCCM is not working properly. It is a circuit with several relays and electrically connections that can go bad individually making for erratic operation.

Have you tested the vacuum actuator? If you have or can rent one of the hand-held vacuum pumps you can test it by pumping on it to see if it holds vacuum. If it does not it could be because the actuator itself is bad or there is a leak in the hose. You might even be able to just suck on it with your mouth if you want to try. The vacuum switch could tested similarly.

I don't know how to test the encoder motor. Perhaps a search of the forum or the web could help with that.

 

Hello Chris

I realize this is an older thread. However, I’m having blazer NVG233 issues as well and i was just wondering what worked out for you as far as your 4x4 issue

thanks,
Dedaike