I recently traded my old k1500 for a 98 bravada, well after i got the truck we noticed that the 4 wheel drive does not work. So I did a lot of research to find out that the encoder motors go bad often. So i changed the encoder motor out and picked up a vacuum actuator up but i can not figure out where it goes. Every where read people say that its under the battery tray but mine is not there? Some people say that it could be on top of the transfer case which would be a trick and if it is up there is it still the same diaphragm style or is it the electronic style? If my 4wd does not work after i change that out what else could be the problem? Can you have the transmission computer flashed? Im new to these truck and do not know much about them besides what i have read, so some info would be greatly appreciated.

 

Have you changed the transfer case fluid (GM Autotrak II ONLY!)?

Did you put the proper AWD (NV136) encoder motor on? Have you checked the electrical connections at the TCCM (located behind the passenger side kick panel)?

The front axle on the AWD trucks is always engaged so you will have no actuator for the front axle.

 

I have not changed the fluid, i will do that today.

The encoder motor i got was specified for a 98 bravada so i hope it's the right one.

Where can i get the fluid? Dealer?

 

so i took the old tcu out and got a new one and still nothing. What senses the slipping that engages the 4 wheel drive? Is it just the rear abs sensor or is there a separate sensor in the rear that tells the computer that its not getting traction?

 

Have you gone through the fuse boxes and checked all of the fuses for continuity? If not, I would do that next.

As far as what senses slip, there are speed sensors on both output shafts which the TCCM monitors. But if there were a problem with either of those sensors or really, a problem with the TCCM and/or Encoder Motor, the 'Service AWD' light would be illuminated on the dash telling you that there is a stored code.

Other than that though, rather than continuing to throw parts at the problem, you may want to consider taking it to someone that has a compatible scan tool that can access the TCCM and determine the cause of the problem. Guessing will prove to waste your time and money further than you already have.

 

Yea I made an appointment to have it taken in tomorrow. Its weird that the service awd light does not come on. I checked all the fuses first and then read about the most common problems, i get parts pretty cheap from a local parts store, the encoder motor was 87 dollars and the tccm i got from a junk yard for 59 so all in all i have not put to much money in it. But im leaning twards there just has to be a problem with the speed sensors.

Im not a GM guy by all means but can figure my way through most problems but this thing has such a weird system that and knowing nothing about it really sucks. If this where a problem with the awd system for a dsm or a vr4 3000 gt i would have 4wd again lol.

Thanks for your help so far ill keep you posted on what the dealer tells me tomorrow.

 

Took it to the dealer yesterday, well the encoder motor and the tccm that i replaced where bad, when the encoder went it took the tccm with it. The tested both of them, and after further inspection they found that the transfer case fuse was blown. So 50 dollars later my 4 wheel drive works and im really happy with the truck. Took it through a bunch of snow and never had a problem this thing goes really well. Wish it was switch controlled though.

Couple of new questions though
1. Is there a 4 wheel low?
2. Im going to get new tires for the thing what tires are good. I was looking at the bridgestone dualers the A/T tread which they can get for 130 a piece plus 50 dollars for mounting and balancing, has anyone used them and do they like them?
3. Now that i have the 4 wheel drive working i would like to change the fluid how many quarts does it hold?
4. I know that the rear has air bags for suspension, when you jack it up is there a way to turn them off? I figure i could just pull the fuse so i dont blow them out.

 

Im glad this issue was solved because my 98 Bravada is going through the same thing... however we got hosed at AAMCO for a new trans and they still did not fix the AWD light.

Its actually so bad now that we are buying a 2005 Chevy trailBlazer to replace the Bravada, and yes the Bravada is or rather will be up for sale... AAMCO told me it was electrical, we did have the S-AWD light however, they tested it said the TCCM was bad, we replaced it all was not good since they forgot to hook the power end of the tccm up, hooked it up still no awd, took it to the local aamco franchise owner and it threw a code indicating that the a/b circuit was open, tech messed with fuses and it kicked into 4wd then dropped a few days later they tell me now it is all electrical and wont do anything about it....

I hunted and all wires are absolutely ok, my gut tells me bad encoder motor, but to go buy new for another thousand for both an encoder and tccm is just illogical since we just threw 2483.11 at the trans all over this "light"

The 98 Bravadas had air ride? my 98 doesnt, im jealous haha

the xcase uses Autotrak 2 fluid only at the dealer, its a bluish purple fluid.

The xcase is also not user changeable when it comes to hi and low settings, various readings are read by the ecu/tccm/sensors and whatnot to determine high or low since the xcase is automatic...

98 upwards the tcase is a 2speed case (either high or low) but its all through the truck and what it "feels" to determine the settings

 

As Taba5 stated, the NV136 in your Bravada is a single speed transfer case (ie. no low range). The NV236 used in the Blazers is a 2 speed.

 

Cool thanks for the info and all the help you guys have given me trying to figure this thing out. I went back to the dealer today and set up to get some new tires, going with the Firestone destination A/T's, And while i was there i got a job haha. (been unemployed for a couple months).