Auto 4WD question

[Austin83]

On my drive in to work this morning I noticed the litty tiny light illuminated above the AUTO selection on my 4WD knob. I think (I hope) that I turned it on 100 miles ago during a rain storm, and I simply forgot about it (It's been dry since). Is there anything that I damaged or could have hurt besides my fuel mileage? I had heard that you could drive it in all the time if you wanted, and you would only notice a drop in MPG. I did notice that my fuel mileage wasn't too good, and I swear I felt a weird sensation when I turned the wheel one time, and at the time I just attributed that to the rubber bushings around the steering linkage in the cold weather. Help ease my fears!! Anything I need to worry about? Thanks in advance.

[AirForceAngler]

^{If all was working properly, you didn't do any damage other than lower your mileage some.}

[Stevens03]

No worries

[Nick The Great]

No problem. I generally have mine in Auto if it is snowing or icy out. It's probably my favorite feature of the truck

[RockySierra]

For any of the GMT-900 owners, you need one of these: http://www.gm-trucks.com/forums/index.php?showtopic=106363&hl=&fromsearch=1

 

I have one and really like it.

[maxco]

You are fine. My buddy drives his in auto 24/7/365... Not sure why...but he does and he's had no problems at all.

[00Silverado4x4]

All is swell, mine gets left in Auto all too often. Definitely a handy feature.

[kstruckcountry]

I've never used it much, as I've been told Auto wears out the front wheel clutch or something. I like to have it locked all the way in. It shouldn't hurt anything, because Auto just keeps the wheels hooked to the axle. Can't hurt to check your diff(might as well do back too) fluid.

[RockySierra]

It is a good idea not to use it unless you need it. The way auto 4WD engages and disengages, it does cause wear and tare on the transfer case and will eventually burn the system out.

[8.1HD/ALLISON]

In auto, the vehicle locks the front axle in (giving you the weird sensation when turning). It then monitors the front and rear wheel speed sensors, and when it sees the rear start to slip the transfer case then engages the front end. When it doesn't need the front it unlocks the front. Yes you will see a slight loss of MPG, No it shouldn't hurt to drive with it in auto. It is a very nice feature for patchy snow, but I wouldnt use it otherwise.

[gmtech4]

In auto, the vehicle locks the front axle in (giving you the weird sensation when turning). It then monitors the front and rear wheel speed sensors, and when it sees the rear start to slip the transfer case then engages the front end. When it doesn't need the front it unlocks the front. Yes you will see a slight loss of MPG, No it shouldn't hurt to drive with it in auto. It is a very nice feature for patchy snow, but I wouldnt use it otherwise.

 

 

90% of what you say is correct ...

 

in 4wd auto the front diff actuator is engaged .....

 

and when the 'putors see wheel slip the encoder motor turns and engages the front output clutch inside the t case and BAM ,4WD is engaged right now ,

 

so fuel milage is a non issue IMHO as the tcase is in 2wd and the frt diff being locked has no driveline effect or strain

 

g'night bitches lol

[kstruckcountry]

With the truck in 2whl, only thing up front turning should be the halfshafts. My understanding is that with auto engaged, the axle, diff and driveline are all spinning. So basically everything that would be spinning in full 4whl is going, except there is no power to any of the front, until the truck decides to send it there. A drop in fuel mileage makes sense, as there's a lot more connected to the front wheels, which the rear wheels now have to push.

[grogol]

I really like the idea of the Auto feature - for patchy ice and snow, or wet conditions, having the 4WD kick in is good peace of mind for me.

 

One thing I've never heard - how long does 4WD stay engaged when the Auto system senses it is needed and engages it? What triggers it to disengage again?

[Z45]

What triggers it to disengage again?

 

Take your foot off the gas.

 

I use AUTO all the time in the winter, unless I am driving a long distance on clear road, I don't notice any drastic drop in mpg but suspect allowing the rear wheels to always spin slippery surfaces wastes just as much fuel as using the AUTO. You got a 4x4 use it.

[Wires]

MPG differences is almost non-existant. After I put a Magnacharger on my 5.3L, I drove in Auto all the time for the 7 years I owned the truck. Nice thing about that is you can nail the gas anytime, and not have to worry about seeing the taillights spin by...

 

The difference between auto and 2H on the highway was about 1/2 MPG (basically nothing).

 

You just need to avoid sharp, low speed turns in the parking lot (when the front wheels chatter, since you can't spin the diff). It's hard on the front diff.