4 wheel drive "Auto" setting

[Brian S.]

Interesting. From my manual:

 

AUTO (Automatic Four-Week Drive): Use when road surface traction conditions are variable. When driving in AUTO, the front axle is engaged, and the vehicle's power is sent to the front and rear wheels automatically based on the driving connections. This setting provides sightly lower fuel economy than 2 (high).

 

Do not use AUTO mode to park on a steep grade with poor traciton such as ice, snow mud or gravel. In AUTO mode only the rear wheels will hold the vehicle from sliding when parked. If parking on a steep grade, use 4 (high) to keep all four wheels engaged.

That's what my manual says as well.

[mike5511]

There is no good reason to drive in AUTO, but you can if you want to, it is your truck. And you are free to believe whatever you want to about. If it makes you feel all warm and fuzzy inside to do so, then by all means, do it! I think those of us who don't, are rebelling at the notion it is the correct thing to do. Not the fact that some choose to do so. So with that, I believe I'll move on. I take away from this thread the fact that when you buy used, you never really know.................

[bertiman]

There is no good reason to drive in AUTO, but you can if you want to, it is your truck. And you are free to believe whatever you want to about. If it makes you feel all warm and fuzzy inside to do so, then by all means, do it! I think those of us who don't, are rebelling at the notion it is the correct thing to do. Not the fact that some choose to do so. So with that, I believe I'll move on. I take away from this thread the fact that when you buy used, you never really know.................

 

 

Hey Mike, I'm sorry that this whole thing has left a soar taste in your mouth. It was never my intent to upset anyone. Please understand, I am not discounting your experience, but rather seeking it. In the end, I'm just a guy who is enthusiastic with his new truck trying to figure what's what. My last few vehicles have been awd/4wd that were always engaged. I actually prefer the way my truck handles in auto mode, especially in the many traffic patterns I face that require "sure-footed" acceleration. The other side of the coin is that I love my frick'n truck and want it to last as long as possible. Unfortunately, GM's documentation, that is available to the general public, is very vague, at best.

 

Anyway, thank you for sharing your thoughts and experiences. And again, sorry if this brought you bad feelings.

 

--Bertiman

[robvas]

Today was a perfect day for AUTO. Why? Some side roads had an inch of packed snow/ice, the main roads were mostly clean and dry.

[Justin MacGillivray]

This is my first truck and the first 4wd vehicle I've had. Previously had AWD Subaru's. I'm impressed with the way the 4wd Auto setting works. Went up to the mountains this weekend for snowboarding with various road conditions and drove the majority in Auto once I got to the bad road conditions. A few times I could feel the truck not finding traction easily so I switched to 4 high and it was fine. I even played in the parking lot of the resort to test the limits of the stock SR-A's and the Auto. I was extremely pleased with the way the truck handled the adverse conditions. But as soon as I got to a lower altitude, I switched off the Auto and back to 2wd.

[mike5511]

 

 

Hey Mike, I'm sorry that this whole thing has left a soar taste in your mouth. It was never my intent to upset anyone. Please understand, I am not discounting your experience, but rather seeking it. In the end, I'm just a guy who is enthusiastic with his new truck trying to figure what's what. My last few vehicles have been awd/4wd that were always engaged. I actually prefer the way my truck handles in auto mode, especially in the many traffic patterns I face that require "sure-footed" acceleration. The other side of the coin is that I love my frick'n truck and want it to last as long as possible. Unfortunately, GM's documentation, that is available to the general public, is very vague, at best.

 

Anyway, thank you for sharing your thoughts and experiences. And again, sorry if this brought you bad feelings.

 

--Bertiman

No you misunderstand. I enjoyed the thread! I just felt I have reached the point where there is nothing new to learn as far as I'm concerned. My opinion hasn't changed on the matter, but I enjoyed following and seeing what others said. Good post!

[Silverado Steve]

Agree with mike5511, if you want to drive around in "Auto" all day everyday, go for it, it's your truck. I don't, don't see the point of having the added resistance on the drive train if it's not needed. I totally understand the mindset of when to use "Auto" vs "4Hi" as I use Auto more often, but I choose to not just put it in Auto and forget it. Also form this thread is why I never....never buy a used vehicle either.

[Jon A]

Traction control and stabilitrac also to reduce wheelspin and the back end from sliding out.

 

 

That's my point, no need for auto in the rain.

 

 

There's certainly no need for it when you don't mind driving like a grandma. Sometimes I don't. Sometimes I do. Traction control doesn't give you any more traction. When you want to take off quickly on a wet road, it simply can't be done as quickly in 2WD as it can in Auto/4Hi. 4Hi will bind the crap out of things, obviously, Auto won't.

 

 

There is no good reason to drive in AUTO, but you can if you want to, it is your truck............

 

There are a multitude of them if you understand how the things work. Beyond allowing acceleration without bind in a way neither 2WD or 4Hi can as described above, I'll bet you did not know the following:

 

For light throttle driving at highway speeds on ice, AUTO will actually give you better traction than 4HI. In 4HI the axles are locked together, this actually causes wheelslip (which is what you do not want on ice) when turning. This is generally one of the big reasons why 4WD trucks aren't nearly as good on icy roads as AWD cars (Subarus, etc).

 

Auto mode, since it does not lock the axles together, does not cause this problem when turning. And above 25 MPH, it always applies a small amount of torque to the front wheels so you can add small amounts of throttle without spinning the rear tires as you would in 2HI.

 

For those who have mostly experienced Auto mode in older GM vehicles, that experience is not very relevant. It did not work nearly as well in older vehicles as there was a much more significant "delayed reaction" where you'd spin the rear tires and then feel the fronts "kick in" after a noticeable delay. On these new trucks, they've done a good job of making the operation very transparent. It's a very useful drive mode in all sorts of conditions. Just because one may be able to "get by" in 2WD on such roads doesn't mean there are no benefits to be had by using Auto mode. That's just setting the bar low enough a poorly performing vehicle can get over it.

[TJay74]

 

 

 

 

There's certainly no need for it when you don't mind driving like a grandma. Sometimes I don't. Sometimes I do. Traction control doesn't give you any more traction. When you want to take off quickly on a wet road, it simply can't be done as quickly in 2WD as it can in Auto/4Hi. 4Hi will bind the crap out of things, obviously, Auto won't.

 

 

 

There are a multitude of them if you understand how the things work. Beyond allowing acceleration without bind in a way neither 2WD or 4Hi can as described above, I'll bet you did not know the following:

 

For light throttle driving at highway speeds on ice, AUTO will actually give you better traction than 4HI. In 4HI the axles are locked together, this actually causes wheelslip (which is what you do not want on ice) when turning. This is generally one of the big reasons why 4WD trucks aren't nearly as good on icy roads as AWD cars (Subarus, etc).

 

Auto mode, since it does not lock the axles together, does not cause this problem when turning. And above 25 MPH, it always applies a small amount of torque to the front wheels so you can add small amounts of throttle without spinning the rear tires as you would in 2HI.

 

For those who have mostly experienced Auto mode in older GM vehicles, that experience is not very relevant. It did not work nearly as well in older vehicles as there was a much more significant "delayed reaction" where you'd spin the rear tires and then feel the fronts "kick in" after a noticeable delay. On these new trucks, they've done a good job of making the operation very transparent. It's a very useful drive mode in all sorts of conditions. Just because one may be able to "get by" in 2WD on such roads doesn't mean there are no benefits to be had by using Auto mode. That's just setting the bar low enough a poorly performing vehicle can get over it.

 

 

HUH...???

 

I have never seen Auto mode work like you are saying, this is not a vectoring system like in AWD. In Auto mode the front transfer case has the clutches pre-loaded at about 10% holding power, the moment the computer senses rear wheel slip it engages the clutches in the front transfer case the rest of the way essentially putting you into 4wd HI mode until the wheel slip goes away and a certain amount of time lapses without wheel slip, then it drops back down into Auto mode and the 10% clutch loading again.

 

You are describing this is like a AWD system that vectors power from front to rear and left to right, these trucks are either locked in 4WD or not. It is a simple system unlike the old Denali system when they were AWD.

[theatasigma]

I leave mine in Auto year round. On some highway trips in the warmer months, I will put it into 2wd since the CC will be set. I really don't notice any difference, I am not a fast driver with my truck so my MPG is somewhat the same in either mode.

[Jon A]

 

 

HUH...???

 

I have never seen Auto mode work like you are saying, this is not a vectoring system like in AWD. In Auto mode the front transfer case has the clutches pre-loaded at about 10% holding power, the moment the computer senses rear wheel slip it engages the clutches in the front transfer case the rest of the way essentially putting you into 4wd HI mode until the wheel slip goes away and a certain amount of time lapses without wheel slip, then it drops back down into Auto mode and the 10% clutch loading again.

 

You are describing this is like a AWD system that vectors power from front to rear and left to right, these trucks are either locked in 4WD or not. It is a simple system unlike the old Denali system when they were AWD.

 

 

Nobody said anything about directing power left and right.

 

Your are using a very simplistic, outdated description of how they work. They are not an on/off switch. The torque load provided by the clutch is variable and tuneable. As stated, at highway speeds they are always sending a small amount of torque to the front wheels. And no, they do not go directly to 100% lockup the instant they detect rear tire slip. It's a clutch pack, it's allowed to slip. The amount of slip vs. time is completely controllable by the computer.

[themiltonkid]

On a side note....it does one hell of a launch from a traffic light in AUTO! Just floor it and go [emoji16]

 

 

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[GulfTango]

Just had 24" of snow and still didn't need 4x4. Lots of weight in the bed from snow and just left it in 2x to see. Never lost traction.

 

 

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[Jeff5347]

OK so I have a simple question as most of this thread answered what I was wondering. Last night since I live in the northeast we got some good snow. Had to go to the store and since this was my first 4wd , I've had an awd, I wasn't sure if I needed 4hi or auto being there was only 2 inches on the ground. So I threw it in auto. My thoughts after reading this is 2wd anytime its nice or even raining as I let my foot control the truck and speed and 4hi if I have some good snow on the ground. If its snowing or ice or I'm off road 4 hi. My question is 2 fold...if I'm in 2wd and feel the need for 4.. Do I need to stop to switch or can I keep driving and go to 4hi? Also... I know this is more of an opinion and I know I'll get 10 different answers...but to not ruin the front axle when is it OK to put it in 4hi? Is a light dusting or say and inch of snow OK or is that to little as around here the main roads get plowed so they're wet and slushy but the back roads are usually covered with a skim of packed snow?

 

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[ic3man5]

Keeping it in auto is the best option in almost all conditions except perfect traction and extremely poor traction conditions... Only thing you lose is mpg drop from the front driveshafts spinning. Stabilitrak will do a better job in auto than 4wd simply because the wheels aren't locked together. The MP2023 also has a 700-800ftlb tq rating so no worries.

 

 

The Auto 4WD position allows the capability of an active transfer case, which provides the benefits of on-demand torque biasing wet clutch and easy vehicle tuning through software calibrations. The software calibrations allow more features such as flexible adapt ready position and clutch preload torque levels. The technology allows for vehicle speed dependent clutch torque levels to enhance the performance of the system. For example, the system is calibrated to provide 06.78 Y (05 lb ft) of clutch torque during low speed, low engine torque operation, and predetermined higher torque for 40 km/h (25 mph) and greater. This prevents crow-hop and binding at low speeds and provides higher torque biases at higher vehicle speeds, in order to enhance stability.

 

During normal driving situations, the transfer case can operate in the Auto 4WD mode. In the Auto 4WD mode, the transfer case shift control module monitors rear wheel slip speed, based on the inputs from the wheel speed sensors and/or vehicle speed sensor. When the vehicle experiences a rear wheel slip condition, the transfer case shift control module sends a pulse width modulated (PWM) signal to an electronic motor, which is the transfer case 2/4 wheel drive actuator assembly. This actuator rotates the transfer case control actuator shaft, applying a clutch. The clutch is designed to deliver a variable amount of torque, normally delivered to the rear wheels, and transfers it to the front wheels. Torque is ramped up to the front wheels until the front wheel speed sensor matches that of the rear wheel speed sensors and/or vehicle speed sensor. Torque is ramped down to the front wheels. The process would repeat if rear wheel slip is detected again.