New here & need help with 4 wheel drive not working

[LT1TONY]

Hello,

First off i'd like to say what a great site this is. This site has plenty of information as I've ready read and learned a few things.

I have a 1999 Chevy Blazer 4 button with the NP8 transfer case code.

My 4 wheel drive hasn't worked in about 2 years and I decided to get it working again. I figured it was the encoder motor as these are known to go bad.

I ended up pulling the encoder motor and pulled the cover off it and as I figured, it was all rusted and looked horrible. I ended up getting a used low mile one from the salvage yard and I also pulled the cover to inspect it. It looked basically brand new and went ahead and put it on.

After installing the used encoder motor I started the vehicle and tried pushing the button and nothing happened. The lights on the 4 button basically light up for a few seconds and then go out again. I actually at one point had the 4 high light on for a while but nothing was engaged as I took it out for a drive to see if it worked. I disconnected the battery twice for about 45 minutes each time and still nothing has happened.

I can hear the encoder motor buzzing below but I don't hear a clunk or that it has moved the transfer case. My question is can the transfer case be bad. I actually turned the transfer case shaft with a wrench back and forth through the different positions and they moved when I had the encoder motor out. It did feel tight while moving it but it did move. Like I said I can hear the encoder motor trying to do something but not sure if it's actually moving the transfer case selector.

I'm kinda stumped for the moment so any information or help would be greatly appreciated.

Thank you,

Tony

[MT-2500]

Originally Posted by LT1TONY

Hello,

First off i'd like to say what a great site this is. This site has plenty of information as I've ready read and learned a few things.

I have a 1999 Chevy Blazer 4 button with the NP8 transfer case code.

My 4 wheel drive hasn't worked in about 2 years and I decided to get it working again. I figured it was the encoder motor as these are known to go bad.

I ended up pulling the encoder motor and pulled the cover off it and as I figured, it was all rusted and looked horrible. I ended up getting a used low mile one from the salvage yard and I also pulled the cover to inspect it. It looked basically brand new and went ahead and put it on.

After installing the used encoder motor I started the vehicle and tried pushing the button and nothing happened. The lights on the 4 button basically light up for a few seconds and then go out again. I actually at one point had the 4 high light on for a while but nothing was engaged as I took it out for a drive to see if it worked. I disconnected the battery twice for about 45 minutes each time and still nothing has happened.

I can hear the encoder motor buzzing below but I don't hear a clunk or that it has moved the transfer case. My question is can the transfer case be bad. I actually turned the transfer case shaft with a wrench back and forth through the different positions and they moved when I had the encoder motor out. It did feel tight while moving it but it did move. Like I said I can hear the encoder motor trying to do something but not sure if it's actually moving the transfer case selector.

I'm kinda stumped for the moment so any information or help would be greatly appreciated.

Thank you,

Tony

What is the tag no. on back of transfer case?
236 or 233?
Any front axle lock in or out?

[LT1TONY]

I'll have to look tonight and check the tag for the number.

Nope nothing is locked in the front.

[MT-2500]

Originally Posted by LT1TONY

I'll have to look tonight and check the tag for the number.

Nope nothing is locked in the front.

Also check for good vacuum to the front axle shifting pancake under battery and for the vacuum switch switching.
It has to have good vacuum and the switch has to switch it for it to pull the cable to front axle.
Any service transfer case light on?
Also run a search here there has been quite a few with same problem.

[LT1TONY]

I'm going to work on it tonight and i'll check the vacuum diaphram under the battery and on the firewall.

The service 4 wheel drive light is on as well and i'll put that on the scanner tonight.

My buddy has a '99 Blazer as well and we might even try swapping some parts out to find the problem.

What do you think about the transfer case? I can hear the encoder motor buzzing below but I don't hear a clunk or that it has moved the transfer case.

If it has vacuum problems will it not allow the encoder motor to shift the transfer case?

[MT-2500]

Originally Posted by LT1TONY

I'm going to work on it tonight and i'll check the vacuum diaphram under the battery and on the firewall.

The service 4 wheel drive light is on as well and i'll put that on the scanner tonight.

My buddy has a '99 Blazer as well and we might even try swapping some parts out to find the problem.

What do you think about the transfer case? I can hear the encoder motor buzzing below but I don't hear a clunk or that it has moved the transfer case.

If it has vacuum problems will it not allow the encoder motor to shift the transfer case?

Find out what one you have and get the code.
And post back code no.
Codes may led to the problem.
Is the buzzing like motor running or just trying to run?
Also check all fuses.

[LT1TONY]

You can actually hear the motor buzzing trying to shift the transfer case but I don't hear the shift of transfer case.

I'll post later tonight the codes and tag number and i'll check the fuses.

Thanks for your help.

Tony

[muddog321]

Remember on Autotrac case (4 button np236)the encoder only activates for 4Lo so get 4Hi working first. Check the firewall mounted solenoid that opens the vac to the actuator and that has to work to couple the front axle and trigger the axle sensor to the TCCM - thats 4Hi - easy. Your front driveshaft always is engaged.

[LT1TONY]

Ok figured out the problem last night. I went thorough and checked everything, from the firewall solenoid, to the actuator under the battery tray and checked vacuum with the hand help vacuum pump.

The problem which was not making my new encoder motor shift was that computer box which is located on the passenger side kick panel. That had a broken chip thus not allowing the encoder motor to work. I put a different box in it and the truck shifts fine now and I can't believe I have it fixed.

I do want to ask one more thing though. The lights on the shift buttons sometime work and sometime don't. Let's say I have it in four high or four low the light won't come on but if I press the button again, it will light up then. Do you think the switch is going bad or is it another connection and that's why the lights come on sometimes and off?

Regardless of the lights, it still operates the function of the 4x4 commands that I want.

Thanks again for all your input.

Tony

[jetfixerdw]

Tony,

I sounds to me like the switch panel is NG. You can find them on ebay for like 30 bucks. If it works ok then I wouldn't worry about. I Just bought a module from gmpartsdirect for $330 bucks. Hope yours was a cheaper than mine. Good luck

David