Using Auto 4wd will not hurt anything. It is there and available if the truck detects wheel slippage. But, the hubs are free, so it's not putting extra load on your transfer case.
You don't want to use 4wd high for long distances on dry pavement.

 

I don't imagine it hurts a thing to leave it in 4WD-Auto. I'm also confused as to why leaving it in 4-HI would have a limit to how far you can drive and what speeds. Why would it? Since when is using your trucks capabilities risking damage?

 

Using 4 hi is fine in a straight line. But as you turn, the wheels turn at different speeds into the corners. Since everything is "hooked together" and trying to turn at the same time, it puts additional strain on the drivetrain. That may show up as tire wear, or early component failure in the drivetrain.
On snowy or icy surfaces, 4wd high is just fine anytime. The tires can then slip ever so slightly on the road surface to compensate for the rotational differences in the wheels.
I use 4wd auto the most. I only go to 4wd high when I know I am going through some seriously deep snow, or if I am going off road.

 

I leave mine in auto unless it's snowing pretty good or it's icy. In the summer, I put it in 2wd

 

When you shift to auto 4 wheel drive, your front axle is engaged so all of the components of your front axle are turning as you drive (front shafts, driveshaft ETC). The transfer case DOES apply a very slight (maybe 5%) rotational force (torque) through an internal clutch to the front driveshaft and because the front axle is engaged, it is ready and waiting for a "slipping event" from the rear axle. When the vehicle senses a difference in speed from the rear axle to the front (rear wheel slip), the clutch within the transfer case applies MORE torque to the front driveshaft to make the front and rear axle turn at the same speed. Kinda like a slightly slipping 4 wheel drive. If the vehicle continues to see a speed differential from the front and the rear axles, the clutch within the transfer case continues to add more torque and eventually will be locked in. As the wheel slip goes away, the transfer case returns to the 5% mode and waits for the next slip event. When you put the vehicle in 4 HI, the front axle is engaged and it receives 100% torque through the internal clutch within the transfer case. A good practice I have found is to NEVER put it in 4 HI on dry pavement. Even if you are going straight!!!! I hope this helps. I believe we have a user on here that works for one of the transfer case manufacturers. Maybe he can give more details. My facts are based on my 2004 Silverado. I assume vehicles today with the same transfer case operate the same way. I hope this helps and as always, READ YOUR OWNERS MANUAL!

 

Thanks for the great info, Gordon. I was pretty sure I didn't want to use the AUTO 4WD function, and you've given me the facts to support my assumption.

I prefer to set it into 4WD when I need it, and be sure I return it to 2WD when I'm done. Based on your explanation, there's a long-term cost associated with the AUTO setting, and since I plan to have my truck a long while, I will continue to give it the best care possible, and avoid expensive repairs later.

 

Pretty much what's already been said, but here's what the owners manual from my 2010 Sierra says:

AUTO (Automatic Four-Wheel Drive) : This setting is ideal for use when road surface traction conditions are variable. When driving the vehicle in AUTO, the front axle is engaged, but the vehicle's power is sent only to the front and rear wheels automatically based on driving conditions. Driving in this mode results in slightly lower fuel economy than Two-Wheel-Drive High.

Notice: Driving on clean, dry pavement in four-wheel drive for an extended period of time can cause premature wear on the vehicle's powertrain. Do not drive on clean, dry pavement in Four-Wheel Drive for extended periods of time.

 

Thanx gordon i was actually going to reply to what u were saying..my brother is an ASE tech and i actually asked him this question a month ago and got the same response. he told me stories of soccer moms who would leave it on all the time in the rain, and anytime they felt unsafe and that they would come in with transmission issues due to this. Thanx for the great info.

 

Thanks for the great info, Gordon. I was pretty sure I didn't want to use the AUTO 4WD function, and you've given me the facts to support my assumption.

Just as a point of clarification, there is nothing wrong with using Auto 4WD. It won't damage the vehicle and only engages when necessarily. Not that you would want to leave it on all the time, but if you are driving on roads with patches of ice or snow, then by all means, use it. Probably the biggest downside to using the Auto mode, is the hit that you take on the MPG's.

 

I agree with bradneal. Occasional use should be fine. The "soccer mom" comment is right on, too. I had a friend who left their Explorer in Auto for the life of the vehicle, and had major drive train issues in under 100k miles (but then again...it's a Ford). Occasional use of auto 4wd on patchy surfaces...no issues. But, get back to 2wd when you don't need 4wd.

 

Years ago, my ex got custody of my '76. She did the same thing - locked-in and drove for months. Finally the front drive shaft broke at the U-joint and came up through the floor board - wazunt purdy.

 

Even when I was still drivin 1500's I RARELY needed 4WD down here in OK. Just during the winter months when it got bad (bad for Oklahoma is different than bad for all you Northies I know). I've actually never used Auto 4WD on anything I've owned.

I woke up one morning at some girls house and got in the truck to go home. When turning the corner I thought what the hell is going on and saw it was in 4LO. No tellin what we did the night before and how far we'd driven it that way cause she lived right off a highway.....lol.

Sorry, this post didn't really contribute to the OP's question.

 

I think as long as you aren't going over 65mph in 4WD high, you should be fine. I know 45mph is the max for 4wd low. Auto mode doesn't have a speed limit that I know of, but think of it this way (as i do): as long as there is enough material (snow) on the road that the front wheels can slip if they need to, then you're fine. Its just that you don't want to run it on dry pavement or it will cause binding from what I know. At least in snow, the tires can "slip" a little even though they are still technically "locked" You may want to use Auto mode for the times when you are in doubt and there isn't much of anything on the road. If there's snow, then 4WD high is fine (or low if you're moving slow enough).

 

Any of u guys notice different noises between the different modes? I'm wondering if I have a bearing bad somewhere or it's the nature of the beast. If I'm driving straight on a smooth road at 35 mph and hit the auto 4wd I can hear the front turning. Nothing loud and most people wouldn't notice it. If I click on 4wd I get a drone sounds. Not grinding or scrubbing noise, more a low groan but definitely noticeable.

 

^^that's because in auto the front diff engages so the whole thing is turning.

In 4hi the transfer case and front diff are both fully engaged so you'll get some noise and weird feel when on dry pavement.

Which is why I don't understand how anyone can drive around in 4hi and not notice. I know if I have my truck in 4 hi and I'm on a higher traction surface, it bucks and chirps with the slightest turn.

Only did that once for about 5 feet haha (was exiting a trail onto a road and needed 4wd right up until I hit the road.

 

Mines an extra cab and 8' foot bed. 4wd and a hard turn and the front hops. There's a lot of speed difference between the front and rear with all that wheelbase.

 

Second what the intelligent men above me said. Even in auto i can hear a difference at slow speeds but I have forgotten it on the highway here and there. Full 4wd I don't see how anyone could forget you have it on, the entire driving experience is different

 

So I just dropped my truck off to the dealer, to have them check on something else, but while the advisor was in my truck he asked if I always leave my truck in 2Hi. (2016 crew cab 4wd) I told him yes. He proceeds to tell me that I should always leave it in Auto. I thought that was weird. I always understood 2 wheel high was the correct setting for normal dry street driving (city driving). This was a good link to reinforce what I knew already.
Why put undue wear on the tranny and lose MPG when no necessary?

 

Don't go by what so yo-yo at the dealer says. Read your owner's manual. LOL

 

So I just dropped my truck off to the dealer, to have them check on something else, but while the advisor was in my truck he asked if I always leave my truck in 2Hi. (2016 crew cab 4wd) I told him yes. He proceeds to tell me that I should always leave it in Auto. I thought that was weird. I always understood 2 wheel high was the correct setting for normal dry street driving (city driving). This was a good link to reinforce what I knew already.
Why put undue wear on the tranny and lose MPG when no necessary?

But you'll miss out on a premature repair by the stealership if you don't leave it auto all the time.

Just sayin

I have to say, I do kinda miss the viscus clutch set up in my old full time AWD Astro.

 

Yeah maybe you should tell that tech to read the owners manual about the auto setting.

Sent from my iPhone using Tapatalk

 

I know on the GMT360 platform (Trailblazer, Envoy, etc) it is highly not recommended to use Auto 4WD because when it detects slippage the transfer case slams into full 4WD and can be pretty hard on the drivetrain, and in one person's case caused him to wreck because the back end broke free, he steered into it, the truck slammed power to the front wheels, which then since he was counter-steering the slide it launched him into a snow bank. I used A4WD on mine once out of curiosity and man, I did not like it. Very jolting when it would throw power, so I used 2HI 95% of the time, and if it was really bad and roads were consistently snow covered I'd throw it into 4HI.

Is the transfer case in A4WD on these trucks - particularly NNBS and newer - smoother and more controlled in its application of power to the front, or does it do the same 5% then WHAM 100%? Last winter I still had the old Trailblazer rustbucket and it really wasn't a bad winter at all, so I never had a reason to use any 4WD mode aside from making sure it worked. Any further winters though I only have the Silverado, and was planning on treating the 4WD the same way, but if A4WD is actually usable it may be nice on those patchy roads you just can't use full 4WD on but are still sketchy.

 

Any of u guys notice different noises between the different modes? I'm wondering if I have a bearing bad somewhere or it's the nature of the beast. If I'm driving straight on a smooth road at 35 mph and hit the auto 4wd I can hear the front turning. Nothing loud and most people wouldn't notice it. If I click on 4wd I get a drone sounds. Not grinding or scrubbing noise, more a low groan but definitely noticeable.

I was noticing a sound coming from my '04 2500 when in auto or 4hi. Not loud but noticeable. I ended up putting a bearing in my transfer case. It's pretty quiet now.

 

So I now have a new transfer case due to my own stupidity. Apparently you are not supposed to tow 2000lbs of snowmobiles on snow covered road with a speed of 55mph in auto4wd for about 100 miles. If you do it burns out the clutches and seizes them causing me to have to buy a new rebuild transfer case. Lesson learned. 2wd or 4hi for me from now on. The GM technician who installed it told don't use auto 4wd at all.

 

a lot of folks don't realize that these do have clutches in them