awd issue

burg99

Original poster
Member
Dec 23, 2012
33
I'm thankful for MoveHere I had no idea things had moved I thought maybe I was just getting snubbed. Heres my question

I know this is not the right place to post this but im in a hurry. This morning i went to go to work and i live in iowa and we got atleast10 inches of snow. Anyways i started out of the drive way and got stuck. Long story short the front wheels are not engaging on my 2003 olds bravavda with sensatrac. No idiot lights on and just replaced the encoder motor last year.

Im not sure if this would affect it or not but my abs light has been coming on and engaging at low speeds. Sometimes the light comes on and stays on until i shut the suv off.

Any help on these issues would be great as i am desperate with getting all this snow and i have a hour drive to work.

Thanks for the help
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Welcome! Might not be an instant fix.

Why did you replace the encoder motor? Same problem?

How many miles, and have you been changing the transfer case fluid every 50K as required?

The wheel hub speed sensors may be involved, especially given the ABS involvement. But a problem with them should throw a code.

A dealer or advanced independent mechanic with a GM Tech II tool or equivalent (you'll have to call a few) can talk to the encoder motor and see if it will move the transfer case clutches on demand. It may be the only way to see what's up. Could be the wiring from the TCCM to the encoder motor, or a speed sensor, or the TCCM itself.
 

burg99

Original poster
Member
Dec 23, 2012
33
Roadie,

Took the bravada to Advance Auto and the only codes were one for back #1 o2 sensor running rich and right front wheel bearing speed sensor erratic. the erratic speed sensor explains the abs issue but not the awd issue. I have 180000 miles on it and I have never changed the transfer case oil. stopped today and got Auto track II to do the job. Any explanation on how to do this would be great.

I originally changed the encoder motor because i had the service awd light on and that is what the code was. havent had a problem since until now. I have had a couple tell me it will probably come back when i get the new wheel bearing assembly on.

As for the o2 sensor im thinking of changing both with 180000 miles it might not hurt.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
burg99 said:
Roadie,

Took the bravada to Advance Auto and the only codes were one for back #1 o2 sensor running rich and right front wheel bearing speed sensor erratic. the erratic speed sensor explains the abs issue but not the awd issue.
Agreed. But what is the exact code they read for the O2 sensor?
I have 180000 miles on it and I have never changed the transfer case oil.
Oooops. It may be toast by now. When you do change it, measure how much comes out and check it for chunks of metal or clutch material.
stopped today and got Auto track II to do the job. Any explanation on how to do this would be great.
By our own fabulous staff member MAY03LT:

[video=youtube;qcjiWgNWD3Q]http://www.youtube.com/watch?v=qcjiWgNWD3Q[/video]
I originally changed the encoder motor because i had the service awd light on and that is what the code was. havent had a problem since until now. I have had a couple tell me it will probably come back when i get the new wheel bearing assembly on.
Not sure why.
As for the o2 sensor im thinking of changing both with 180000 miles it might not hurt.
It could. The downstream (post-cat) sensor almost never goes bad. Much more likely it's telling you that there's a problem with the cat. The upstream (pre-cat) sensor often gets sluggish around 100K miles, and we change them same time as the plugs. BTW, did you do the plugs and ALL fluids at 100K, even if you ignored the transfer case? What you need is a scan tool that can read real-time data to look at the exact readings of your O2 sensors, then you will know with some certainty what needs changing. There are a lot of DIY systems on the truck, but you need to tool up to work on them. Or cultivate an honest independent mechanic to start a relationship with.
 

burg99

Original poster
Member
Dec 23, 2012
33
Well today i finally got around to changing the right front wheel hub and the erratic behavior of the abs is gone. Finally changed the transfer case oil after 180000 miles. the oil was a little dark but still had a tint of blue to it, and i removed approx. 1 and 3/4 quarts. didn't think that was bad for the mileage. all this done I still have no awd, back tires just spin in the snow and fronts never kick in. i have no service awd light on, and again encoder motor was changed a year ago. this was done because the service awd light came on and the code read was the encoder motor. All was good until recently. i still think it all started with the faulty abs sensor on the right. I'm not sure if it is a fuse or the tccm needs to be reset or if everything needs to be reset. Any help would be great.
 

CaptainXL

Member
Dec 4, 2011
2,445
Irratic operation is kind of a dead giveaway. I would check Alldatadiy.com or similar source for TSB's related to ABS. I know there are a few and one of them is related to a loose ground at the frame for the ABS. I would also check fuses.
 

1978chevy4x4

Member
Dec 30, 2012
14
I am having the same issue. I put mine up on four jack stands so all wheels are off the ground, then started it up and put it in gear. At first the rear wheels spin only then at about 30mph the front engaged. I got out and applied pressure with a 2x4 and was able to stop the wheels. To me this seems as though everything is functioning except the clutch pack/viscous coupling. At this point in my project I am stilling trying to solve whether its the actual clutches or the lockup solenoid. o yea Im woking on 02 Bravada that has smart trak with gm/np 126 transfer case.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Required reading for how the transfer cases work: Offroadtb.com Transfer Case Operation: NVG 226 (NP8)

For the AWD NP126 version, ignore the stuff about LO range. Another difference is the encoder motor has only 5 wires instead of 7 because it doesn't have the motor locking solenoid to prevent inadvertent on-the-fly shifting into LO range at 75 MPH if the normal NEUTRAL and speed interlocks failed, which would be an exciting event. :eek:
 

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