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Citykid

By Citykid
in Engines & Drivetrain

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Citykid Enthusiast

Citykid

Posted
Posted

2017 1500, 5.3.  I have the option to switch to 4H, 4L, AUTO and 2H.  When in AUTO the dash says I'm in AWD.  Do we have this option? 

I had my tranny fail on me and when I went the the tranny place I happened to be in AWD (it was raining).  He lectured me like I was driving 4x4 on a paved road. "You're not up north with snow, you don't use that on roads!"  My manual doesn't say a thing on this.

 

This isn't a AWD vs 4x4 thread.  Or I hope it's not.

CamGTP Senior Enthusiast

CamGTP

Posted
Posted

Just keep it in 2WD unless otherwise needed.


Having it in auto didn't cause the transmission to be damaged nor does it cause any other real wear on the front diff either.

Z45 Senior Enthusiast

Z45

Posted
Posted (edited)

I use AUTO every winter since they started putting in GM trucks and NEVER have any issues.  Anyone telling you to never use it, don't know what they are talking about IMO. Its there for reason, so use it when necessary.  

 

Acquaintance is a state police canine officer and he has a Tahoe PPV and he is told to keep it in AUTO 24/7.  Has had a couple Tahoe's so far and never lost the transfer case yet.  Image them go over 130mph in AUTO?

 

Here is GM info on that; I only copied info pertaining to AUTO

 

Quote

The purpose of this bulletin is to help explain the operating characteristics of 4WD/AWD systems.
excerpt:
Automatic Transfer Cases
Automatic transfer cases will have the characteristics of both the Part-Time 4WD and the AWD systems depending on the mode selected. If the transfer case is operated in 4HI or 4LO, it will behave as a Part-Time 4WD system. If it is operated in the Auto 4WD mode, it will behave like an on-demand AWD system.

 

AUTOMATIC TRANSFER CASES
The last category is a combination of 4WD and On Demand AWD. These transfer cases have a 2HI, Auto-4WD, 4HI, 4LO and Neutral position and would fall in the general 4WD category. This transfer case has the operating characteristics of both an On Demand AWD and a Part-Time 4WD system depending on the mode selected. This transfer case uses a clutch pack to allow for a difference in speed between the front and rear axles in the Auto-4WD mode. In the 4HI or 4LO modes, there is no allowance for the difference in speed between the front and rear axles.


 

 

Edited by Z45
  • Like 3
mikeyk101 Senior Enthusiast

mikeyk101

Posted
Posted
35 minutes ago, Z45 said:

I use AUTO every winter since they started putting in GM trucks and NEVER have any issues.  Anyone telling you to never use it, don't know what they are talking about IMO. Its there for reason, so use it when necessary.  

 

Acquaintance is a state police canine officer and he has a Tahoe PPV and he is told to keep it in AUTO 24/7.  Has had a couple Tahoe's so far and never lost the transfer case yet.  Image them go over 130mph in AUTO?

 

Here is GM info on that; I only copied info pertaining to AUTO

 

 

 

That is an interesting bulletin. With the Auto 4wd, how does that affect MPG? I know that using the full time 4wd, the gas mileage takes a hit over regular 2wd. I would think that the Auto may also cause a slight drop as well.

CamGTP Senior Enthusiast

CamGTP

Posted
Posted

It's still in 2WD for 99% of the time. The auto just allows it to engage the transfer case when required. Where as the 2WD keeps it from doing that.

  • Like 3
  • 4 weeks later...
truckguy82 Senior Enthusiast

truckguy82

Posted
Posted (edited)

Imagine your engine spinning your trans, and then the trans spinning the rear driveshaft.

 

when you select awd, it essentially engages a clutch between the front and rear driveshaft. 50% power sent to the front is the same as the two driveshafts being locked together in rotation.

 

The range is 5-50% power sent to the front when awd is activated. It will send power to the front based 3 things.

-Throttle input, WOT launch = 50% power to front. (This is why there is no detectable delay in traction, because it is throttle activated)

-loss of traction at the rear tires

-your speed(over a certain mph, it likely won’t send power to the front based on throttle)

 

There is almost no reason to use 4wd hi in these trucks…..unless, you are driving in an area where the awd clutches will activate so often that it could overheat them, such as a snow covered road or off roading.

 

Nowhere on the forums has anyone tested this data, but I do now own a new jeep and it had pretty much the exact same transfer case and someone hooked up a scan tool and provided all the parameters in which activate it. It all made sense how it worked.

 

One surprising thing is that in the jeep, above 25mph, it sends significantly less power to the front axle even in 4wd HI! I really assumed the transfer case would be locked in 4hi, but it’s not. Obviously to protect the drivetrain if you accidentally leave it in 4hi.

 

Edited by truckguy82

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