First let me apologize in advance if I have missed an FAQ on this somewhere...everything I have seen has been directed at push button 4WD systems.

The AWD in my 01 Bravada currently does not work. For a time when my father in law owned it the Service AWD light was on. Then after he replaced the battery it went out, but a drive during the following winter clearly indicated that it was not working. He gave the vehicle to us a recently and I would like to have it operational for this winter. Since I have had it, I replaced a wheel bearing which cleared the ABS light, but the Service AWD light does not come on at start up or while its running. I have checked the AWD fuse and it is good.

I am at a lose on where to start on this as all of the diagnostics I have seen relate to the Blazers with push button systems. Any direction here would be much appreciated!!!

 

To properly diagnose the 136 transfer case in your Bravada, a full feature scan tool capable of controlling the encoder motor is required.

I went through this a few winters ago with a friend that has a 2000 Bravada AWD and used my Autoenginuity scan tool cable and associated software on my laptop to control the transfer case. Being on snow helps a lot as you can see which wheels are under power. We could not get the encoder motor to move regardless of whether it was mounted to the transfer case or not even though it was getting the proper power and commands from the TCCM (we back-probed the connections at the encoder motor to test for power & PWM signal). The fix was to replace the encoder motor.


The NP/NV136 transfer case uses a preloaded clutch pack to power the front axle and is very sensitive to fluid type and condition. This typically does not cause the clutch pack to slip excessively under full lock conditions unless it has completely burnt up which can happen if the wrong fluid is used and/or the fluid is neglected for far too long.


I would start by replacing the transfer case fluid using Autotrak 2 fluid. It is pricey, but is the recommended fluid for the transfer case. You'll need just shy of 2 quarts of it which should run you around $16 total from your dealer parts counter.


You can also pull the TCCM connections and check for corrosion. It is much more typical on the NV236/NV233 transfer cases than it is on the NV136, but corrosion can still affect the inputs/outputs of the TCCM and it's operation. The TCCM is located behind the passenger side kick panel below the dash, in front of the door.


If neither of those result in the transfer case engaging as it should and you do not have access to a full-feature, bi-directional scan tool, you can try changing out the encoder motor. Check with the store you are buying the replacement from to see if they will accept returns if it doesn't end up being that component, rather deeper inside the transfer case or the TCCM itself.

 

Thanks so much for the feedback and direction. I will change out the fluid this weekend and check the connectors. Since my father in law bought it new, I know it has never been abused but am a little concerned about the transfer case fluid. He rarely drove in weather that needed it but I am not certain if he ever changed it. I'll get a good feel when I change it this weekend and advise.

 

OK, I changed out the transfer case fluid with AC Delco Auto Track II as recommended. The fluid that I pulled out looked like transmission fluid that was slightly worn. I did not see any metal flakes in it. I then pulled the negative battery cable and then removed the connections off the TCCM and did not see any corrosion. I put dilectric grease on the connections and then reinstalled.

After hooking the battery cable back up I still did not get the "Service AWD" light when I first turned the key on or when it was running. I drove the truck about 5 miles to a construction site with a lot of loose dirt and tried to see if I could get the front wheels to lock. Admitted this was difficult to determine as I didnt take anyone with me but I thought I could at least get the "Service AWD" light if it was something electronic. At any rate, I could tell for the most part that the front wheels did not lock and I did not get the service AWD light.

I plan to move next to the Encoder motor as I do not have the Autoenginuity scan tool nor do I know anyone that has one. I do want to say the front end felt a little tighter on turning after the fluid change but that could be my imagination.

Swartlkk, does this behavior sound right to you without having the "Service AWD" light coming on? I hoped that by disconnecting the battery and then cleaning the TCCM connections I could at least get that to come on. I have check the fuse before and after and it is fine.

Thanks again and sorry for all the questions.

 

If the light doesn't come on at start up or at any time then maybe your little bulb is burnt out. Take it in to have the codes read and see if it is kicking out a code. Most auto parts places have a code reader you can use for free.

 

The bulb is an led that is soldiered to the board so I can't replace it. Also the parts stores just have the regular OBD2 scanners and they cant pick up anything related to the TCCM, or so they have told me. I'll check again however to be safe.

I have Torque and an OBD2 bluetooth adapter and it doesn't pick up anything either. Based on what Swartlkk said it sounds like full feature scan tool to go there.

 

So I did some more reading and am starting to find information on this problem...guess I should have searched for "service AWD light"...anyway I found this statement:

"A faulty TCCM could cause the system to just hard fault and not illuminate the 'service AWD' light on the dash, but other problems (such as an encoder fault or a problem with the transfer case itself) should cause the light."

I pulled the TCCM and checked for voltage using a test-light on the read and orange wire coming into the TCCM and my check light gets nothing. I checked the 4WD fuse and its good as well as has power when I put the test-light on it. Does the TCCM not get power until the truck is in drive? I didn't test that out, but it would seem that it would need to be powered whenever the vehicle is on.

I know I seem like I am grasping here, however I don't want to throw money at it to fix it that isn't going in the right direction. I checked the fuse block under the dash and didn't see anything like a relay for the AWD system but I could have missed it.

If this is normal then I'll move on to the encoder motor, but I just found it odd that I am getting no Service AWD light at all and then I saw this previous post.

Thanks again for looking!

 

On my friends truck, the problem with the encoder did not illuminate the Service AWD light. Without testing using a full featured scan tool, you are just guessing between a faulty encoder and a faulty TCCM. how lucky do you feel?

 

Shortly after I bought my '00 Blazer Trailblazer the "service four wheel drive soon" message displayed. I had it diagnosed at the Stealer who said the module was bad and quoted $580 for the repair. First he said $380 for repair and when I said ok he said, Oh, and that didn't include $200 labor. I declined, got a rebuilt module at the parts store for $220 and it was literally a fifteen minute change. I will say it was worth the $95 for the advanced diagnosis. If everything else seems ok, check that module.

 

Thanks for the info....that was my concern. Did your friends truck light up the Service AWD light when it first started up (part of the Xmas tree lighting, so to speak)? I certainly dont feel lucky enough to throw parts at it

I feel better moving to the encoder motor now based on this....thanks Swartlkk!