dumb qestion..diff between 4x4 &AWD?

[AirJunky]

Wow, sounds like a big o can o worms to me, CoveredAv. Sorry to hear your still battling it. Maybe this additional exposure will attract some moderator's attention to the problem.

The encoder motor/sensor issue you outlined in a couple different thread was exactly the nature of my question. I never saw a followup on your fix. Did replacing the sensor (only) actually resolve your issues getting in & out of 2 & 4wd?

I ask because I'm at the same point with my own Av. It is temperamental about going in 4hi or back to 2hi. Usually turning off the truck & then restarting it will get it where it needs to be.

For example, today, I'm driving around in town on compact snow & ice using the Auto4 mode. I get on the freeway, which is dry & clear & go to put it in 2hi, it flashes for about 30 seconds, then goes to 4hi. So I pull over on the onramp, stop the truck for 5 seconds. Restart the truck, hit the 2hi button, and it goes in just fine. Then I proceed on to the freeway in 2wd.

I'd consider driving in Auto4 on the dry freeway but in the parking lot at work, on a paved lot, barely any snow on it (plowed), the truck in Auto4, and it has a tough time making any corners, which tells me that the encoder motor is not shifting the truck into 2wd as the Auto4 should do.

 

[CoveredAV]

Wow, sounds like a big o can o worms to me, CoveredAv. Sorry to hear your still battling it. Maybe this additional exposure will attract some moderator's attention to the problem.

The encoder motor/sensor issue you outlined in a couple different thread was exactly the nature of my question. I never saw a followup on your fix. Did replacing the sensor (only) actually resolve your issues getting in & out of 2 & 4wd?

Yes.  No problems since.  Replaced the encoder SENSOR ONLY.  Not the whole encoder motor.

I ask because I'm at the same point with my own Av. It is temperamental about going in 4hi or back to 2hi. Usually turning off the truck & then restarting it will get it where it needs to be.

Are you getting a "Service 4WD" message in the DIC?

Have you had a full featured (not just OBD-II) GM scan for codes?

Do you have a current subscription to OnStar, whereby you might obtain any trouble codes?

For example, today, I'm driving around in town on compact snow & ice using the Auto4 mode. I get on the freeway, which is dry & clear & go to put it in 2hi, it flashes for about 30 seconds, then goes to 4hi. So I pull over on the onramp, stop the truck for 5 seconds. Restart the truck, hit the 2hi button, and it goes in just fine. Then I proceed on to the freeway in 2wd.

But since this is related to 4WD, Auto 4WD, and transfer cases, we can probably sneak this aspect in, as long as the OP doesn't mind?

I'd consider driving in Auto4 on the dry freeway but in the parking lot at work, on a paved lot, barely any snow on it (plowed), the truck in Auto4, and it has a tough time making any corners, which tells me that the encoder motor is not shifting the truck into 2wd as the Auto4 should do.

You are experiencing more functional/dysfunctional issues than I did.  Mine was mostly an electrical/signalling problem, reporting values not expected by the comunicating modules, which generated a code that pointed directly to the culprit... the encoder motor sensor.

Your symptoms seem more developed... approaching the mechanical level as well as electrical.  Obviously, trouble code  provide the clearest map for accurate diagnostics.  I have a list of what the codes related to the transfer case mean, so when and if you can pull yours, I'll be glad to use my list to help interpret what systems/parts  the code's suggest looking at first.

 

[AirJunky]

Thanks CoveredAv..... and to lordvette for the threadjack.

I have not had the truck scanned yet. And I don't have an Onstar subscription. I guess I will be talking to the dealer service dept in the morning to get that done. I'll let you know what I find out.

Also, since PM isn't working, let me know how to best reach you.

Just got thru that thread Sperry posted on the various AWD & 4WD systems. Very interesting stuff. Definitely worth checking out.     

 

[ms38w]

Heres the thread.

Wow, now theres some reading to do MS3.

Hey CoveredAv. I PMed you some time ago about the encoder problems you had & possibly solved. Did you get the PM?

Great thread link...
  I had a 2003 GMC 2500HD 2wd that had a similar traction device.  When I parked on an icey incline, put it in park, and it started sliding down hill, it sensed the front wheels moving forward and the rear wheels not moving at all and automatically reversed the rear wheels in an attempt to prevent the truck from sliding down hill.  The ice, however, won.

 

[DigitalBoy0101]

Woah, ms38..........I just read your story on your site and looked at the pictures. That is going to be ONE BAD RIDE when you're done!

............please tell me you're done?


..........almost done?


I'd drive all the way to San Antonio on my days off work during Nationals just to see that.

 

[longbeard]

Typically 4WD or 4x4 is a mechanical system involving the transfer case, front differential & front hubs & delivering a more locked up system than AWD, hence the reason that it shouldn't be driven on dry pavement (front wheels don't turn at the same rate as the rear so they push / pull the rear around).

AWD systems typically have some smarts involved too (a computer controlling which wheels get power). As one wheel gains / looses grip, the system will redistribute torque to the other wheels. This setup is constantly changing as you drive. I have never seen an AWD system that delivers a fully locked 4wd in addition to AWD.

All that said, with the various traction management systems being added to these trucks, the lines between the two systems are becoming pretty tough to define. I've wondered if the Auto4 system in our Avs is really just an AWD function. One key piece of that system is the encoder motor & sensor. If that part isn't working correctly (which is not uncommon, is it?), then the Auto4 system doesn't engage & disengage correctly as traction changes. Since we've been driving snow packed roads the last month or so, I have felt my own Auto4 system NOT disengaging correctly as the truck is getting good traction....... you can feel the truck start to "hunt" as your driving, steering gets a bit stiffer, etc.

No clue how Cadillac's system works. Or what about the Denali?

thanks for the explanation.