Slipping or stuttering in 4wd auto mode -- is this normal?

[Yukon not UConn]

Just had a rainy weekend with the family in Asheville, NC. We rented a cabin in the mountains and drove a lot in low-traction conditions. We live in Florida where it's mostly flat, so haven't really seen many hills or gravel roads with the Yukon. For no really good reason, we've pretty much kept it in 4wd Auto mode since we bought it. Our other vehicles are all AWD, so just assumed this was a safe driving mode. Anyway, while driving around Asheville in the rain, we were continually getting slipping or stuttering which I though felt like a transmission issue. By the end of the weekend, I was convinced we had a transmission problem. I brough it to our dealer yesterday to have them check it out. First thing the service writer did was notice it was in 4wd auto and told me not to drive it like that. We agreed they would run the diagnostics and if there was no transmission issue, go ahead and perform the 90k maintenance on the transmission and 4wd system as it just happened to roll over 90k miles on the trip.

In the end, they did not find any problems and did the transmission and 4wd system service (I would have done these myself, but one less thing I need to do). They are saying I experienced normal functioning in 4wd auto mode and in the future just run 2wd high or 4wd.

Does this seem accurate? Is this how the 4wd auto mode should feel in low-traction situations when it is "toggling" between 2wd and 4wd? While I'm happy there isn't a transmission issue, now I'm concerned the 4wd auto mode might not be properly functioning.

A couple caveats: I have warranty coverage to 100k miles, so if there is an issue, I want to get it sorted in the next 6 months. I definitely understand the difference between AWD and 4WD. My other vehicles are/have been Audi Quattro, Acura SH-AWD, or Hondas.

 

[WillCO]

Operating the vehicle in 4WD auto mode is not problematic; it's the way GM intends us to use these. It's an automatic system that allocates torque according to traction conditions; having the vehicle in that mode all the time is pretty much the point. Not sure what your dealer was concerned about.

If you drive these in 4WD High or 4WD Low, you may encounter a little hopping when you turn the wheel driving at low speeds. Simplified, this is happening because these trucks aren't sophisticated enough to vary wheel speed on the same axle and if you get into the physics of a moving car with all 4 wheels driven, turns out the inside wheel in a turn needs to be spinning a little slower than the outside wheel. Without this correction, that wheel does trip and stutter a little. It's nothing to worry about.

If you happen to have summer tires (seems unlikely but I'll cover it anyway) and the temperature is below about 50 degrees, you might feel more hopping yet because the tread compound on the tires gets really hard as they get cold, and they grip less. I have a Porsche 911 in Colorado and it does this all winter long.

It's not clear from your post that what I described above is what you're experiencing, as you seem to be feeling the stutter with the truck in 4WD Auto. It's possible in certain condition you'd feel it anyway in 4WD Auto if the truck happened to be driving the front wheels at the exact right time, but it would be really situational and hard to create on purpose.

Fun user name, BTW.

 

[Yukon not UConn]

Will,

This was occurring mainly while driving up fairly steep inclines of gravel roads or wet pavement. Based on my discussion with the GMC tech, I was given the impression that I was feeling the system toggling in and out of 4wd when the rear tires would slip. It was also happening under strong acceleration on wet roads (such as a highway entrance ramp). I'd guess some combination of rear tire slip, traction control activation, and 4wd activation could cause what I was feeling. I was thinking repeated short transmission slips in the moment.

The story behind my username is this: When I first bought my Yukon and was connecting the wifi service, the service person asked me for an 8-digit password. To which I said, "Yukon123". The service person repeated this to me as "Yukon123" then spelled it out: "U-C-O-N-N-1-2-3". I had never before thought about those two words sounding exactly the same. She must have been located in the Northeast, lol.

 

[WillCO]

Will,

This was occurring mainly while driving up fairly steep inclines of gravel roads or wet pavement. Based on my discussion with the GMC tech, I was given the impression that I was feeling the system toggling in and out of 4wd when the rear tires would slip. It was also happening under strong acceleration on wet roads (such as a highway entrance ramp). I'd guess some combination of rear tire slip, traction control activation, and 4wd activation could cause what I was feeling. I was thinking repeated short transmission slips in the moment.

The story behind my username is this: When I first bought my Yukon and was connecting the wifi service, the service person asked me for an 8-digit password. To which I said, "Yukon123". The service person repeated this to me as "Yukon123" then spelled it out: "U-C-O-N-N-1-2-3". I had never before thought about those two words sounding exactly the same. She must have been located in the Northeast, lol.

Interesting. I suppose it's possible you managed to find the limits of the automatic 4WD's switching capability. These trucks are great products, but probably not at the vanguard of technology in many areas, especially drivetrain.

Now that I'm thinking about it, when I know for certain I'll be driving in a low traction situation (usually snowpack for me), I generally reach down and engage full-time 4WD in order to eliminate the lag between when the truck feels the wheelslip and engages the front axle. Maybe you felt that lag as well.

If it's any comfort, I had a 2004 Explorer for a long time, the "AWD lag" on that thing was far worse.

 

[steiny93]

Using 4wd auto in high traction scenarios is problematic, don't do it.
GMC says the same: https://www.gmc.com/gmc-life/how-to/when-to-use-four-wheel-drive.

What you describe is the outcome, the stuttering is the couplers engaging / disengaging and the play in the driveline makes it hyper noticeable.
Also, if you get rough with the throttle when in 4wd auto, and the vehicle goes between high and low traction, you can cause yourself a world of heartache (couplers will let loose).

If you would have switched to 4wd the stuttering would have stopped.

 

[swathdiver]

Right, Auto is for temporary use, like rain storm. Folks who leave it in Auto are first in line to have their transfer cases rebuilt.

Even though you are in Florida, run the transfer case through its paces every so often to keep it in good form and ready when you need it. We do ours at least once a month even if only in the driveway and swale for a few yards.

 

[WillCO]

Using 4wd auto in high traction scenarios is problematic, don't do it.
GMC says the same: https://www.gmc.com/gmc-life/how-to/when-to-use-four-wheel-drive.

Although not always optimal for efficiency and wear of your vehicle 4wd driveline, AUTOMATIC 4 HI can be used on any road condition without risk of damaging your vehicle.


?

 

[Fless]

Although not always optimal for efficiency and wear of your vehicle 4wd driveline, AUTOMATIC 4 HI can be used on any road condition without risk of damaging your vehicle.


?

So, not damaging, but not optimal for wear. Long-term wear = damage, from my perspective. I'll save my transfer case clutches for when I need them.

 

[WillCO]

So, not damaging, but not optimal for wear. Long-term wear = damage, from my perspective. I'll save my transfer case clutches for when I need them.

Better said.

 

[BlaineBug]

Although not always optimal for efficiency and wear of your vehicle 4wd driveline, AUTOMATIC 4 HI can be used on any road condition without risk of damaging your vehicle.


?

I have never read that, everyone else I have seen posting in similar threads about 4x4 Auto always states that "it is not designed to be used full time but only during times of unknown road conditions that vary between slick and dry."

Although I know people who leave it in 4x4 auto full time regardless.

I leave mine in 2-HI but for the first 34,000 miles I didn't own it I have no idea how it was used.

 

[WillCO]

I have never read that, everyone else I have seen posting in similar threads about 4x4 Auto always states that "it is not designed to be used full time but only during times of unknown road conditions that vary between slick and dry."

Although I know people who leave it in 4x4 auto full time regardless.

I leave mine in 2-HI but for the first 34,000 miles I didn't own it I have no idea how it was used.

The difference would be that I posted text from the actual GM owners documentation and you've been reading chat board posts by, well...whomever.

Vive l'internet.

 

[Sam Harris]

I use my 4wd Auto in rain storms out here in Texas. When I was in Colorado, I’d just use 4Hi if I was concerned about slipping around too much in the snow.

 

[Larryjb]

I believe that many AWD systems use a fluid couple between front and rear, whereas the Tahoe is a mechanical couple activated with clutches. That would explain why you are able to drive other AWD systems without feeling the jumping around.

 

[Sam Harris]

I believe that many AWD systems use a fluid couple between front and rear, whereas the Tahoe is a mechanical couple activated with clutches. That would explain why you are able to drive other AWD systems without feeling the jumping around.

As well, the AWD systems have the functionality of adjusting slippage on the fly, as in a certain amount of torque to each wheel, while with our auto 4wd, it just engages and disengages the front wheels entirely. (AFAIK)

 

[BlaineBug]

The difference would be that I posted text from the actual GM owners documentation and you've been reading chat board posts by, well...whomever.

Vive l'internet.

I understand that totally. Previously I have described auto-4wd as a "full time all wheel drive" system, personally. Isn't it nearly identical? A lot of the older generation GM full size SUVs had no ability to select 2wd and were constantly in 4x4. My Wife's Nissan Rogue also has full time 4wd with the ability to "4x4 lock" at the press of a button, and my Father's 2003 Element had full time AWD with no selections to make whatsoever (sold that in 2016.) I assume these full time AWD systems use clutches in their transfer cases just like GM does when you use "auto 4x4" mode.

 

[WillCO]

I understand that totally. Previously I have described auto-4wd as a "full time all wheel drive" system, personally. Isn't it nearly identical? A lot of the older generation GM full size SUVs had no ability to select 2wd and were constantly in 4x4. My Wife's Nissan Rogue also has full time 4wd with the ability to "4x4 lock" at the press of a button, and my Father's 2003 Element had full time AWD with no selections to make whatsoever (sold that in 2016.) I assume these full time AWD systems use clutches in their transfer cases just like GM does when you use "auto 4x4" mode.

Snarkiness aside, I can objectively see how a mechanical differential that activates the front axle based on slippage at the rear would be engaging and disengaging the front differential a lot more often than a dedicated AWD system that always has it engaged at some level. In the same way as flipping the light switch causes a lot more wear on the light bulb than having the light on does, this approach could wear the system prematurely.

It makes sense. Question is whether it's material, and more specifically whether the impact of the wear is material enough to offset the disadvantage of having to activate the AWD when you feel you need it, or if you forget.

Long ago I had one of those Mitsubishi Montero Sport SUVs that had a manual 4WD differential. To activate 4WD I had to reach down and shift a lever (though at least I didn't have to get out and lock the wheels). One time I was driving along the highway after a freeze in 2WD, hit some ice, and ended up piling the thing up against the guardrail. The world will never know whether or not having the front axle driven might have kept me from spinning out completely because I didn't think to have 4WD on at that moment.

 

[Geotrash]

Long ago I had one of those Mitsubishi Montero Sport SUVs that had a manual 4WD differential. To activate 4WD I had to reach down and shift a lever (though at least I didn't have to get out and lock the wheels). One time I was driving along the highway after a freeze in 2WD, hit some ice, and ended up piling the thing up against the guardrail. The world will never know whether or not having the front axle driven might have kept me from spinning out completely because I didn't think to have 4WD on at that moment.

With a 4wd SUV running in 2WD mode without traction control in variable icy conditions, when that backend breaks loose, it can be nearly uncontrollable. I had a '99 Isuzu Rodeo that scared us silly on wintry roads a handful of times until I got in the habit of putting into 4WD when the roads got slippery.

 

[WillCO]

With a 4wd SUV running in 2WD mode without traction control in variable icy conditions, when that backend breaks loose, it can be nearly uncontrollable. I had a '99 Isuzu Rodeo that scared us silly on wintry roads a handful of times until I got in the habit of putting into 4WD when the roads got slippery.

It's safe to say that experience changed me forever as a driver. Whenever I see people driving like morons on slick roads, now I always think "ah, you haven't had your accident yet."

I was actually on my way from Denver to Colorado Springs to make a sales presentation. After the wreck the truck was still drivable, I actually continued and did the meeting.

 

[Larryjb]

A long long long time ago, we had to get out and lock hubs to use 4WD.

Then came along automatic hubs, but you still had to lock them for full time 4WD.

Sometimes they'd get stuck in the locked position and we'd have to drive backwards for a few feet to be able to unlock them. In bad cases, we had to jack up the wheels to release the tension to be able to unlock them.

The AWD systems (on our Explorer) are good for my wife, so she doesn't need to think about it.

 

[BlaineBug]

Snarkiness aside, I can objectively see how a mechanical differential that activates the front axle based on slippage at the rear would be engaging and disengaging the front differential a lot more often than a dedicated AWD system that always has it engaged at some level. In the same way as flipping the light switch causes a lot more wear on the light bulb than having the light on does, this approach could wear the system prematurely.

It makes sense. Question is whether it's material, and more specifically whether the impact of the wear is material enough to offset the disadvantage of having to activate the AWD when you feel you need it, or if you forget.

Long ago I had one of those Mitsubishi Montero Sport SUVs that had a manual 4WD differential. To activate 4WD I had to reach down and shift a lever (though at least I didn't have to get out and lock the wheels). One time I was driving along the highway after a freeze in 2WD, hit some ice, and ended up piling the thing up against the guardrail. The world will never know whether or not having the front axle driven might have kept me from spinning out completely because I didn't think to have 4WD on at that moment.

I also owned a 1995 Jeep Cherokee from 2005-2011 with a manually activated lever actuated 4x4 NP231 transfer case with 2hi, 4 hi, 4 lo, and neutral. Some Jeeps also came with a NP242 I believe it was called which had all of the same functions but also had a full time 4x4. One of my friends had a 1997 Jeep Grand Cherokee which had a full time 4x4 transfer case which still allowed you to shift into neutral or 4x4 LOW but had no ability to shift into 2 wheel drive mode. Whatever the model of that transfer case was had the tendency to fry the clutches (especially on 33's, quite a bit larger than the stock tire size,) and he had to replace his transfer case multiple times - however, when it fried the clutches, you always ended up with rear wheel drive versus no wheel drive! (or maybe it was front wheel drive? I don't remember, that was a long time ago!)