4wd Auto

[spenpet]

hello all!  I did a search and didn't have much luck with it...I have kind of a two part question about 4wd auto feature...

 

1) I understand that you can use it 'all the time' if you want, but how does it work?  is it like all the front drive is fully engaged but in neutral?  so all the parts gears, clutches, etc are getting used but no power going to them?  if so, does this promote potential premature wear-out of these parts?

2) how long does it take to engage when your computer senses a wheel slip/ have you felt it being effective/ when have you used it?

 

Thanks in advance!

 

hope everyone is staying warm...its brutal out there!

[Ryno12]

I don’t consider Auto 4WD an “all the time” feature. I only use it in patchy or semi slippery conditions. I’m mostly in either 2WD or 4WD and only use the Auto when conditions call for it. I do believe driving in Auto all the time causes premature wear. It’s unnecessary on dry pavement and also noisy.

There’s multiple threads that came up on a search. Here’s just one.

http://www.gm-trucks.com/forums/topic/162486-driving-in-4x4-auto/

[spenpet]

thank you! and thanks for the link!  when i searched it said nothing of the topic (i knew that wasnt true, but just couldnt find it)

[aseibel]

if using 4 auto, when your rear tires start to slip, the clutch will grab and engage the front in a fraction of a second.

 

There's been a lot of heated discussion about this if you care to read old threads. I'll try to sum up the useful parts:

- you "can" drive in 4 auto all the time if you want. It may cause some additional wear. It may reduce fuel mileage slightly. But won't blow up your truck.

- there is no point in using 4 auto when roads are good.

- when roads are bad and you are actually driving on ice or snow, just use 4 hi.

[Crstfr]

only in rain and ice... other than that.. 2wd...

[Nick The Great]

In my '07 I got to the point where I'd put it in Auto when is was a little sloppy out.  I never noticed much fuel economy difference or anything.  

 

But in my '17 I can 'feel' a little different in the truck in Auto on dry pavement.  I think it's in my head, but I feel like something's spinning under there?  

[Mike GMC]

That would be the front drive shaft.

[Pearl2017]

Lat week was at the sand dunes for holiday pulling a toyhauler. I left and forgot the 4x4 Auto on, down the highway a bit I noticed the trans temp was high and mileage was worse and enabled the off-road page in OSD where it showed 4x4 mode. I switch Auto OFF but the indicator did not go to 2x4 until i lifted off the cruise control. So either there was some tire slippage hitting the on ramp or the mode would not switch 2x4 till the drivetrain was "Unloaded". I think there is some wear and tear having it on as heat and -mileage was evident.

[newdude]

In AUTO, the front axle locks, and the transfer case and the transfer case control module are the deciding factors on power going to the front wheels or not. 

 

Quote

During the Auto 4WD mode, the power flow is the same as it is in the 4HI mode. Except, during the Auto 4WD mode, the 2/4 wheel drive actuator assembly (13) rotates the control actuator shaft to the correct torque level positions. Rotating the control actuator shaft to the various positions changes the clutch torque level. When a difference of front wheel speed to rear wheel speed is recognized, the transfer case control module commands for more or less clutch torque.

 

[Nick The Great]

1 hour ago, Mike GMC said:

That would be the front drive shaft.

Well yeah.  But I don't think I should be able to feel it like that.

 

I never did in my 2007.  Maybe it was broken and I never knew 

[Mike GMC]

That's the down fall of having such a quite refined vehicle, any little change is noticable.

[NWI Denali]

9 hours ago, aseibel said:

if using 4 auto, when your rear tires start to slip, the clutch will grab and engage the front in a fraction of a second.

 

There's been a lot of heated discussion about this if you care to read old threads. I'll try to sum up the useful parts:

- you "can" drive in 4 auto all the time if you want. It may cause some additional wear. It may reduce fuel mileage slightly. But won't blow up your truck.

- there is no point in using 4 auto when roads are good.

- when roads are bad and you are actually driving on ice or snow, just use 4 hi.

^nailed it.