2002 Bravada AWD not working.

lovesrugers

Original poster
Member
Jan 25, 2012
30
Hello All new member who was referred over here from Trailvoy. Anyways here is what I wrote over there.

Ok a few months ago my wife's Bravada started doing the crow hopping thing while making low speed turns. Easy fix. I changed the differential fluids and the transfer case fluid problem solved. After doing this the Bravada ran down the road smoother than I can ever remember. In fact it was running so smooth I started to worry if the AWD was working or not.

Well I found out this week with our first big snow storm that the AWD is not working at all. I managed to get the car stuck a few times and all that would spin were the back wheels. Finally on the last time it was stuck the service AWD light lit up. Upon the next engine restart the light went out again.

Now that things are starting to warm up around here I finally got a chance to start looking things over. First off I had my father in law come over with his scan tool. Upon hooking it up and programing it into the Bravada we found code C0374, malfunction in the AWD system. According to the tool this code is set if the rear wheels spin for 10 seconds or more.

I was really hoping to find the TCCM dead due to my model year and the ease of the fix but alas I need to go deeper.

At first my father in law thought it might be one of the sensor's on the drive shafts. A quick trip in the remaining snow with the scan tool hooked up monitoring the drive shaft speeds confirmed they were working properly, and yes we cleared the trouble code before doing this drive. During the drive I demonstrated to my father in law that the front axle would not engage at all.

According to the scan tool the wire harness to the encoder motor may be to blame.

Since I don't want to get wet I haven't had a chance to crawl under the SUV and look at the encoder motor and harness. Heck maybe it came loose some how, but I figure I am not that lucky.

Anyways I suspect I most likely need a new encoder motor but I want to test it for proper operation before buying a new one.

So how do I do this. I have read I can remove it from the vehicle and apply 12 volts on the bench to see if it is working. How exactly would I go about doing this. I am pretty sure I can get it out of the vehicle but how do I test it?

Next off if it fails the test and I buy a new encoder motor from the local parts shop, O' Reillys, NAPA etc does it come with the encoder sensor?

Finally will I need to have the new encoder sensor programmed by a dealership?

Thanks for any help that can be provided.

Jerry

Updated question:
Is there any encoder motor brand or place to get them that is preferred over others? I am going off the assumption that I am going to find the wiring harness ok and am going to need the motor.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
I think if it isn't the wiring, it's the motor. Here's the schematic, except the AWD vehicles don't have an electric brake on the encoder motor. Aftermarket units should have the sensor, and no need to submit yourself to dealer abuse for any programming ripoff.

3141d1327507696t-4wd-inop-1.jpg
 

lovesrugers

Original poster
Member
Jan 25, 2012
30
Thanks that should be a big help.

Now that I have that info what is the best way to test the wiring besides just looking at it? Would I need to disconnect both ends of the harness and test for continuity or is there a better way?

I am assuming there is nothing special in removing and installing the encoder motor. Just unplug harness, remove five bolts, pull motor. Place new motor in, install bolts plug in?

Also I believe I need the motor for transfer case NP126?

One last question I am seeing a huge variance in price between different vendors for this part. Can anyone recommend a good place to get this part? I know I can order it in to my local parts store but I am seeing the same part online for nearly $100 less. The Bravada can sit for a bit while I wait for parts to save that kind of money.

Jerry
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
I would go underneath with a meter and just check for typical voltages while the motor isn't moving. It's hard to set up an AWD vehicle with the right amount of wheel spin except on a lift. A high end scan tool like the GM Tech II could talk to the TCCM and command it to do things and look for the encoder motoro sensor, but paying a mechanic to do that might cost more than the new motor.

You can take the motor off and bench test it.

Yes, it's an NP126. Rockauto.com using one of their 5% discount codes (available on this site) is usually the cheapest. I have no information that there are doggy aftermarket suppliers to be wary of for this product.
 

lovesrugers

Original poster
Member
Jan 25, 2012
30
Thanks Bill.

Looks like Rockauto it is. I believe others have recommended them to me in the past.

It is supposed to dry up on Friday or Saturday around here so that looks like the day I will be crawling under to see whats up.

Jerry
 

lovesrugers

Original poster
Member
Jan 25, 2012
30
All right I finally was able to get the Bravada up on stands yesterday and today. After much fiddling around I finally got the stupid connector to the encoder motor apart. Due to its location I couldn't really examine it in depth like I wanted to but it appeared ok. Anyways before reassembling the connector I decided to liberally douse it in electrical contact cleaner. Once it dried out I reassembled and tested out the Bravada.

For a first test I just found some loose gravel and spun the tires. Of course the ground is frozen so I couldn't tell much if the front axle engaged or not. It wasn't till I went to make a sharp U turn that I found out that it was engaged and I was crow hopping pretty badly. After driving in a straight line it once again unlocked the axles and I was able to turn.

Next off I went and found a pretty steep hill that had ice on the top of it and loose gravel on the bottom. I pulled the Bravada up on to it and stopped and then tried to go up. As usual I got a bit of wheel spin from the back tires and then up I went. After backing down I once again made a sharp turn back onto the asphalt and found myself crow hopping but it once again cured itself after going straight on the road for a few feet, ok probably 25-50 feet.

So it appears the system may be working normally again. I believe it is normal to have slow engagement of the AWD system for the Bravada. I am also pretty sure the crow hopping is normal due to me forcing it into AWD mode and then driving directly onto a solid surface.

Anyways what do you guys think. Is the encoder motor fine? Is the wiring harness ok. Should I take it apart one last time, clean it again and then put some dielectric grease on it?

Jerry
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
I'm a big fan of dielectric grease, especially down there. Sounds like your functional test is OK, except for the residual crow hopping. That sounds like grabby transfer case clutches, which could be old or low fluid. I forgot to ask earlier, I think, but had you been changing it religiously every 50K miles before the change you mentioned? How many miles do you have, and how long ago was the last transfer case service? How much fluid ran out then before you added the new stuff? Running it with old or low fluid could have damaged the clutches, making it behave the way it is now.
 

lovesrugers

Original poster
Member
Jan 25, 2012
30
I admit I had no idea the transfer case had a 50k mile change on it. I didn't become aware of this until I had the initial problem last summer. When I did change it the case was full and the fluid looked fresh. Currently the vehicle has 93k miles on it or so. When you say Transfer case service do you mean just change the fluid or something more in depth. I performed the last fluid change in August or September of 2011.

Looks like after I get off work tommorow morning I am going to put it back up on the ramps and take the connector apart, clean it, and then grease it good. Hopefully this will keep everything in working order for our next snow event.

Jerry
 

lovesrugers

Original poster
Member
Jan 25, 2012
30
Well that fix didn't last long. Once again the AWD is inoperative. Now I am wondering if it is the wiring harness or the actual encoder motor itself? One thing I left out of my repair yesterday was that I did smack the encoder motor itself a couple of times. Kinda like you do with an inoperative fuel pump or starter to hopefully get it to work so you can get home. No idea if this is what made it work temporarily or what.

Oh yes it has been dry here for the last few days so the harness should still be nice and dry with no moisture in it.

One other thing, I spent last night looking over any thread I could find on any forum about this problem. Main issue is no codes stored and the front axle won't engage. It appears this has been a common problem over the years. The scary part is that I found where people have been taking their Bravadas into the dealership for repair and the dealership basically just keeps changing parts till the problem is fixed. This is not a solution as far as I am concerned. Ok, I can pretty much change all the parts that the dealership would change with the only cost being parts but...

So what do you guys think, go after the encoder motor next?

Jerry
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
I'd do the encoder motor, yes. Or take it apart and see if you find grease on the position feedback sensor (like a potentiometer) or damage in the gear train. If you can find a mechanic with a high end scan tool that can talk to the TCCM, they can force the encoder motor to go through its paces. That might cost more than a new motor.

The threads you might be seeing about front axle engagement are often discussing 4WD, not AWD vehicles, where the 4WD vehicles have a splined disconnect on the front passenger side that physically disconnects the passenger CV shaft during 2WD mode. You don't have that. No front axle actuator. Just a permanently engaged splined collar. A lack of front axle torque for you and the AWD vehicles can only be due to the transfer case not engaging the clutches to send any torque forward.
 

lovesrugers

Original poster
Member
Jan 25, 2012
30
Thanks Bill,
I have access to a high end scan tool but I can most likely get a new encoder and install it before I can get a chance to get the scan tool and use it again.

When I did my searching around last night I focused specifically on the Bravada due to it having a different front axle than the Trailblazer or Envoy. Now that I think about it I probably should have included the Rainer and the Saab because I believe they also share the Bravada's AWD system. I am sorta glad I don't have that splined disconnect because it appears that causes headaches for a few TB and Envoy owners.

Now time for the funny story that this issue caused last night. While at work last night I found a nice patch of snow to go into. Of course it is now frozen solid snow but it should work for my purposes. I easily got into it until I was stuck. Time to back out. While doing so the front bumper scrapped a bit and I managed to rip off the lower valance and dislodge the front bumper cover. I also managed to break the passenger side fog light mount. Ugg.:mad:

This left me laying on the ground at two this morning putting the front bumper cover back on and reinstalling the lower valance.

As soon as it gets light out enough I am going to head out and repair the fog light and you won't even know anything happened. Next time I will have to remember this is not my truck with its metal bumpers and to back down a little slower so as not to cause the front to bounce and catch on the nice packed snow.

Jerry
 

lovesrugers

Original poster
Member
Jan 25, 2012
30
Well I got the new encoder motor installed. So far I think the AWD is working properly again. To bad the forecast calls for sun for a bit so I don't have access to anything really slick to test it out on. I did try the hill test again and it briefly spun the back wheels and then seemed to apply power to the front wheels so I could continue on up the hill. So far after all my tests in loose gravel and the hill test I have yet to see the vehicle exhibit the crow hopping condition I was having before. Hmm maybe it was the encoder motor or sensor that wore out last summer?

Oh yeah I documented my change out of the motor and put a quick write up in the articles section for those that want to see what changing the encoder motor looks like.

Jerry
 

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