Bravada AWD Problem

[suzy1052]

I lurked around this site before joining and I think I have come to the right place. I recently bought an 02 Bravada with 150xxx on it and it runs good except for the awd. I cant get it to engage what so ever. In fact the service awd doesnt even light up at key on.I cant imagine its burned out since its an led. I checked ALL related fuses and did the fuse pull. All fluids are at the proper level and the encoder motor turns when jumpered to a battery. With the front end off the ground both tires turn independently but not like they are connected to each other. The front shaft is engaged but neither wheel would turn however you could feel the driver side cv shaft bump a little but nothing on the passenger side. I noticed that the encoder motor harness was disconnected when I first noticed I had no awd so I figured the p.o. just unhooked it for some reason and thats why the service awd light wouldnt turn on. I'm just wondering if I should look for a tccm problem or a intermediate shaft bearing problem on the front diff. I really like this truck even after owning a 2002 and 2010 Explorer but I would like to get this awd thing under control if possible. ANY help will be appreciated.

 

[IllogicTC]

If both wheels can turn independently, you might have a problem up front where the front-axle disconnect would be (I don't know what it is on the AWD system, but it's not a disconnect). I would think the driver's wheel should be easy enough to turn when the system is off. The clutch should be at 5% for the front in the TC, it'd provide a bit of resistance but turning using the outer diameter of the wheel should allow you to overcome it.

I'd be willing to bet either the encoder motor has a problem (just because it turns when hotwired doesn't mean it can engage the internals of the TC), or perhaps the TC has a problem, and the encoder motor isn't able to overcome it. Get a 10mm hex bit and 2 quarts of Auto-Trak II GM transfer case fluid, and change it out. When it's draining, it should either be blue or have a "bit" of a look like old dish water. If it looks excessively bad, there's your first problem right there - it's supposed to have had its fluid changed 3 times by 150k miles.

If you receive less than 2 quarts in your drain pan, that's also a likely source of problems, and damage. The TrailBlazer and Envoy has an "A4WD" selector option, which is very similar to the Bravada's AWD, and we're usually recommended not to use it. With the finicky nature of the NVG-126 and -226 models with their stupid clutch system, any problems with the fluid can easily start causing damage to the clutch pack.

If you'd like a service manual on the NVG-126 (AWD) transfer case, check the top sticky post in Technical Discussion. If you'd like a little different one that includes exploded views of the internals, here you go.

Others may actually have experience in this and can advise you further and confirm/deny my theory, but in the meantime it doesn't hurt to have a look through those service manuals to learn a bit more about the system.

 

[Juicy K]

With the front end off the ground both tires turn independently but not like they are connected to each other.

Just to clarify, with the front end up in the air. You turn one wheel and the other does nothing? Since the front is an open diff with both wheels in the air the if your turn the driver side as if the truck is traveling forward, the passenger side should move in the opposite direction. Is this the case? If not is the front prop shaft moving when you spin one of the wheels?

 

[IllogicTC]

Just to clarify, with the front end up in the air. You turn one wheel and the other does nothing? Since the front is an open diff with both wheels in the air the if your turn the driver side as if the truck is traveling forward, the passenger side should move in the opposite direction. Is this the case? If not is the front prop shaft moving when you spin one of the wheels?

On second thought I'm more curious on why the previous owner thought to disconnect the encoder motor's harness. That's why I'm pointing more toward the transfer case. Something smells really fishy there, it's kinda crap that the previous owner wasn't at least up-front about it, and I kinda have a feeling Roadie's going to about it and give the usual speech about checking all that stuff out lol. And as the resident four-wheel expert, he'll probably know what's up to.

 

[Juicy K]

Thinking about the service AWD light, does it come on when you start the truck. I have seen some shady people take out check engine light bulbs so people dont see that light. I am pretty sure if the TCCM does not get a response back from the Encoder Motor that throws up a flag (Service AWD light).

 

[IllogicTC]

Thinking about the service AWD light, does it come on when you start the truck. I have seen some shady people take out check engine light bulbs so people dont see that light. I am pretty sure if the TCCM does not get a response back from the Encoder Motor that throws up a flag (Service AWD light).

I don't think the encoder motor does any checks on startup though. It does, however, do checks when a different position is commanded than the one it's currently at, and uses the feedback to determine which "adapt-ready" position it's in, which way it's going to move and how far to move to reach the new desired position.

With all this snow and ice on the ground (at least up this way) it would be trivial to get the AWD system to try sending more power up-front, and if that doesn't pop a lamp then I'm curious as to what else would be going on that somehow isn't tripping the lamp. Perhaps burnt-out clutches could, after all there's no feedback to ensure the power's being sent up front that I know of, it just turns the encoder motor to the correct position and assumes it's all working properly.

A decent scan tool should be able to pull any codes which may have been stored, also. Perhaps something would turn up in the history.

 

[Juicy K]

Here is what I am getting at.
Shady Joe wants to sell a car but the check engine light is on, is Shady Joe more likely to fix the problem that is causing the computer to throw the code? Chance loosing money on the car because a lot of people would be turned off by a check engine light? Or would he remove the light so the possible new owner does not know there is a problem?

I just went out to my 2002 Bravada (in the cold) just to verify. When the key is turned to the on position the Check Engine light is on, Reduced Power, ect... One of the lights that are on is the Service AWD light. (Key in the ON position, engine not running) After seeing that, I started it the lights ran their checks and went away.

I am just curious if his Service AWD light even works. If it does not the OP would have had no clue the AWD didnt work until he needed it and it didn't work.

Just wondering if the bulb was removed to hide the fact the Encoder was not hooked up thus setting off the light.

Sorry I have a hard time trusting people, especially when it comes to money.

 

[suzy1052]

On second thought I'm more curious on why the previous owner thought to disconnect the encoder motor's harness. That's why I'm pointing more toward the transfer case. Something smells really fishy there, it's kinda crap that the previous owner wasn't at least up-front about it, and I kinda have a feeling Roadie's going to about it and give the usual speech about checking all that stuff out lol. And as the resident four-wheel expert, he'll probably know what's up to.

Heres what happens : When the the front wheels are off the ground the front prop spins freely with only the slightest movement of the drivers side wheel and nothing from the passenger side. If I turn either wheel the prop does not move at all. When the front wheels are on the ground the front prop doesnt turn it will only bump back and forth and when I hold the driver side cv boot you can feel it bump when you try to turn the shaft.

 

[suzy1052]

Here is what I am getting at.
Shady Joe wants to sell a car but the check engine light is on, is Shady Joe more likely to fix the problem that is causing the computer to throw the code? Chance loosing money on the car because a lot of people would be turned off by a check engine light? Or would he remove the light so the possible new owner does not know there is a problem?

I just went out to my 2002 Bravada (in the cold) just to verify. When the key is turned to the on position the Check Engine light is on, Reduced Power, ect... One of the lights that are on is the Service AWD light. (Key in the ON position, engine not running) After seeing that, I started it the lights ran their checks and went away.

I am just curious if his Service AWD light even works. If it does not the OP would have had no clue the AWD didnt work until he needed it and it didn't work.

Just wondering if the bulb was removed to hide the fact the Encoder was not hooked up thus setting off the light.

Sorry I have a hard time trusting people, especially when it comes to money.

I really dont think the guy I bought it from knew the awd was out as he's only had it since Oct. and when I opened the gauge cluster to check for a burned out light everything looked good. The led for the awd lamp was still in there. I checked the color and level in the tc and everything looked up to snuff. If the light worked at all I would be leaning toward the intermediate shaft because of the passenger wheel not having or taking any input but since its not I'm holding out hope for an easier and less expensive fix but who knows ?

 

[IllogicTC]

When you turn a wheel and the prop does not move, does the wheel on the other side spin in the opposite direction that you're turning? If not, it may be something with the intermediate shaft or another part of the drivetrain leading to the passenger's side. The AWD system has no disconnect for the axle, while it's not a solid axle it's still all full-time mechanically-linked.

If he's only owned it since Oct., then what about the owner before him? Someone somewhere must have decided to pull that connector, and I just wonder why. I'd still see if there aren't any codes that could be pulled, it can also tell you other things about the vehicle you didn't know.

On second thought, disconnected it SHOULD send a service-system flag up because there is no feedback signal being returned from the reference voltage, which is odd. Not like disconnecting the encoder would solve a front-axle issue, it'd just alleviate some of the stress going up there if it was disabled in the lowest clutch setting.

 

[suzy1052]

When you turn a wheel and the prop does not move, does the wheel on the other side spin in the opposite direction that you're turning? If not, it may be something with the intermediate shaft or another part of the drivetrain leading to the passenger's side. The AWD system has no disconnect for the axle, while it's not a solid axle it's still all full-time mechanically-linked.

If he's only owned it since Oct., then what about the owner before him? Someone somewhere must have decided to pull that connector, and I just wonder why. I'd still see if there aren't any codes that could be pulled, it can also tell you other things about the vehicle you didn't know.

On second thought, disconnected it SHOULD send a service-system flag up because there is no feedback signal being returned from the reference voltage, which is odd. Not like disconnecting the encoder would solve a front-axle issue, it'd just alleviate some of the stress going up there if it was disabled in the lowest clutch setting.

Turning one wheel does not make the other turn at all in any direction which has me thinking intermediate shaft. Its just that that dang bang no awd light has me stuck before moving on to hard parts. Maybe it is burned out too and I have a series of different problems. I only have a 39 dollar code reader so I know looking for a stored code is useless on my own.

 

[IllogicTC]

If there's no stiff resistance when trying to turn the passenger wheel, sounds like something's definitely broke up there. The AWD axle is full-time linked together. There's no noise or anything when you're driving it?

 

[Juicy K]

May not be a bad idea to put one of the front wheels on the ground, and turn the lifted one. It does sound to me something mechanical is broken in the front end. Since there should be movement wherever the least resistance is weather it be the opposite wheel or the prop shaft (when both are in the air).

For the Service AWD light, just turn the key to the ON position and see if it lights up. If it doesnt, I would get that replaced so in the future (after the mechanical problem is figured out) you will know if something goes or it is starting to act up.

 

[suzy1052]

There is no noise from up front at all. One of my thoughts is that someone deleted it because they didn't want to fix it which is fine if it was done the right way and I'm moving to SC this summer lol. The alley mechanic in me just wants to know what the hell is going on ! Of all the problems I had and fixed on the 2 Explorers and there were a bunch the 4x4 wasn't one of them so this is a new arena to me. I pulled the rpo codes and it looks like its got a 3.73...will one from any of the other gm360's work ?

 

[suzy1052]

UPDATE...I found a front diff , shaft and connect bearing on CL for 200.00 and picked it up yesterday. Today I took everything apart and found that the intermediate shaft was stripped on the oil pan bearing side. I greased up the new shaft and bearing and installed them and now everything works. I haven't stayed outside this long in 20 degree weather since the 7th grade but it was worth it. Thanks everybody for their input.

 

[djthumper]

Thanks for the update! I am glad you were able to get this resolved with the help of the site.