Buick AWD not working

[BR53L]

Hi everyone. First post, but I did a little research before starting another AWD thread. Hoping to get some direction/troubleshooting.

I have an 05 Rainier 5.3l with ~140K. Bought it 3 months ago. When I got it it had one newer tire and 3 worn tires. I noticed the AWD would turn on in parking lots and start chunking on me after I purchased the truck. I noticed in the service history that the new tire was on the vehicle for 4k miles before I replaced all the tires. The AWD also worked well for a short time after and no more chunking in tight turns. Now since the snow came I have been messing around off-roading with friends the service AWD light came on and I lost AWD and got stuck. I turn the truck off and the light goes out, but the AWD is not working. The service light comes on only after spinning the rear wheels for an extended time and goes out with each key cycle. It seemed it was intermittently active and now just gone for the past week. I also noticed on 2 occasions the ABS light turned on/off, but that is functioning properly as far as I can tell. I have changed the xcase fluid with autotrak 2 and it was only slightly discolored compared to the new fluid.

I have hptuners, but I can only communicate with the engine/transmission. What things should I check for before stopping by a shop that can read the codes? Any tests I can do myself?

Thanks in advance.

 

[The_Roadie]

A high end scan tool or GM Tech II can command the encoder motor through its range of motion and confirm if it's jammed. But my guess is that excessive awd system activation when the tire sizes were mismatched has damaged the encoder motor. You can put in an aftermarket replacement for cheaper than an hour at the dealer for their diagnostic.

 

[BR53L]

Thanks for the quick response. Happen to have the encoder motor part number handy? Are their non-gm variants of this part?

 

[C-ya]

Look at RockAuto Parts Catalog. Navigate down through Buick/2005/5.3 and then pick transfer case. Expand Motor and look there. It lists NP4 and NP8. Look in your glovebox and see which RPO code you have. I can't remember if the Rainier is all-time A4WD or selectable.

 

[BR53L]

Its NP4. Looks like rock auto has them for 125 and summit has them for 145 with free shipping. It is Dorman 600904 for the NP4.

Hoping to snag a scan tool from a friend later to read the transfer case codes that Im sure are stored. I just hate ordering parts without being 100% certain its the issue, but I want it fixed this weekend as well. I'll post as I figure stuff out.

 

[linneje]

I just hate ordering parts without being 100% certain its the issue, but I want it fixed this weekend as well. I'll post as I figure stuff out.

The range of items causing your problem is pretty narrow, so in this case I think you are going to be OK with the part fixing the problem. The people posting advice for you are pretty knowledgeable on the 4WD systems on these platforms. Let us know how it turns out.

 

[BR53L]

^ I know and I appreciate the help. I've seen a lot of the same users posting advice so I am getting used to another forum. I ordered the encoder motor from summit to make sure I have it before the weekend. I won't get a scan till Wednesday. If it points to something else I'll just ship it back.

 

[BR53L]

Ok heres my update after a scan. Please chime in if you have anything to add.

C0035
U1017
C0374
Also had a throttle body code but I forgot what it was maybe p2119er...position code. Never threw a cel though so Im blaming that on the -25f temps we've had.



C0035 is the left front speed sensor... that would explain the abs malfunction. Weird thing is when the abs light came on I was on the accelerator. I will check those connections.

U1017 comm issue?

C0374 found a thread on gmt http://gmtnation.com/f24/2002-bravada-all-wheel-drive-not-working-1523/

This guy seems to have the same issue as I am having in his bravada even down to the initial chunking. hopefully its the encoder motor as it was for him.

Also I have another question. Does the AWD engage with just the fr/r shaft speeds or does it account for the wheel speed sensors as well?

 

[The_Roadie]

The TCCM only looks at the two driveshaft RPM sensors. Wheel hub sensors connect to the ABS control module.

 

[BR53L]

Replaced the encoder motor this morning. Fixed the issue. AWD is working really well. It kicks in much faster than it was before as well.

What an easy job. After checking out another gmt thread showing the install, I was able to do it in 30min before work this morning.

Thanks for the help!

Now I can move on to some more general maintenance.

 

[linneje]

Glad it worked out. There are many articles and posts here to help with different work. Stay in touch, you may find that you can save yourself a lot more money and headaches by using the information on the forum.