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4x4 Auto ?


morrislee

Question

I have always been suspicious about electronics that are labeled "Auto", can someone explain to me what the Auto under 4x4 knob in my 2014 1500 GMC Sierra is really doing?

 

Is it "auto" as in variable power distributed between 4 wheels based on tire traction? Like AWD? 4x4 under low speed and switches back to 2wd above a certain speed? This is not very clear in the user manual, how does it know when to switch to 4x4 is the real core information needed, "based on driving conditions" is not very clear to me.

 

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, and the vehicle's power is sent 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.
Also, when it is in 4x4, how much power is distributed to the front? How much to the back? or is it 50/50 on these trucks?
If there is somewhere I can find thee information, great, because I do not know what key words to look for....Sorry!!
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On my 2011, Auto 4WD works very well. Best I can determine, it works much like our Jeep SRT. A small amount of power is going to the front (maybe 5%) and as needed more power is shifted to the front via the transfer case clutch packs. Slippage of the clutches allows steering without the lockup of full 4WD mode.

 

Our 2002 Yukon had Auto 4WD but it was terrible.

The system in the 2002 and 2011 are basically identical I believe. Very similar function (if it's working right).
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I've had partime 4WD forever (almost) and I'm so used to just switching into 4hi anytime the roads get slick w/ snow. I guess it would be hard for my brain to comprehend putting it in Auto 4WD and trusting it'll actually be working. LOL Versus just putting it in 4WD like I always do.

 

Does the Auto 4WD help prevent fish tailing when the roads are just slightly wet/greasy? You know how trucks can get in 2WD - no weight on rear wheels, slight moisture on the road and making turns...... (aged tires don't help either)

 

Thanks again for help!! There are just certain questions / answers that you cant' get by searching google!!

Traction control and Stabilitrak also fill in a few roles with keeping your vehicle pointed straight. It's not just simply the auto-4wd system

 

If there's snow on the ground I usually keep the truck in auto, and if the snow is deep or really coming down (think driving in a snow storm or when there's 6" of snow out and plows didn't come out yet I just throw it in 4HI and leave it there so I don't have to wait that 1/2 second for the front wheels to kick in when I need it.

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On my 2011, Auto 4WD works very well. Best I can determine, it works much like our Jeep SRT. A small amount of power is going to the front (maybe 5%) and as needed more power is shifted to the front via the transfer case clutch packs. Slippage of the clutches allows steering without the lockup of full 4WD mode.

 

Our 2002 Yukon had Auto 4WD but it was terrible.

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From what I am reading here, the auto 4x4 behaves just like the traditional posi-trac differential works. Puts a tight clutch pack between front and rear differentials, and the clutch pack will slip once there is enough "pressure" difference between front and rear axle. On a traditional 4x4 system in 4 wheel drive on dry pavement, the chassis will actually start to twist up until something gives, usually one end of the truck will slip the tires on the pavement eventually.

 

A viscous coupler behaves very much like a torque converter, when one side of the coupler begins to spin faster than the other side, the oil between them will drive the slower spinning side. Like two fans, facing each other, with oil between them instead of air, the spinning oil will drive the slower fan until speed matches. They could even set these up to lock up electrically when auto is moved to 4x4. Most AWD systems use a viscous coupler.

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The system in the 2002 and 2011 are basically identical I believe. Very similar function (if it's working right).

The auto 4wd in the 2002 must have not been working correctly then because it seemed to be in/out rather than than proportional control. The operation of the 2002 Auto 4WD was one of the reasons I hesitated buying the Jeep but after I drove one at the Track Experience that concern was gone.

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The Auto is based off the front/rear wheel speed.

 

As soon as the rear slips under power, the front will kick in and pull it to wherever the wheels are pointed.

 

My understanding is that the auto system applies more power to the front at higher speeds than lower speeds. So it would help with fishtailing some. But if conditions are that sketchy I just use full 4x4.

I'll second that. I use 4 auto only to get the truck moving but if I'm in the muddy, snowy type conditions of stop and go, I'll just lock it in 4hi.

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2hi to 4 auto is on the fly. There is no minimum or maximum speed for the option to engage. Depending on the road conditions at the time you hit the button will determine if you hear any additional noises. In my truck if I hit 4 Auto on paved road I hear no additional noises at all. However if I'm driving on my dirt road it has made a couple extra thumps as the rear may be slipping a little and is trying to kick the truck into 4wd right off the bat.

Thank you sir.. [emoji106]

 

Sent from my SG Note 4 on Tapatalk

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Awesome feedback gang!! THANK YOU!!!

 

When I bought my current truck 9 years ago.... there wasn't any/many trucks available with all those traction control devices on them (again - Toyota not offering it). The only traction control I have, is a mechanical LSD in the rear! LOL But then again, 9 years ago I wouldn't have cared and couldn't afford it.

 

See ...you guys are starting to really sway me. I just hope the overall size & test drive is as impressive.

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Auto 4x4 is on demand, it is in 2wd and and when the rear wheels start slipping, TC locks up and engages the front axle. Once traction is equalized, the TC unlocks the front axle and goes back into 2wd mode.

 

I drive all winter in AUTO, unless I am driving on completely bare roads, which is infrequent in my locale. Lake Superior dumps a lot of snow on this part of Upper Michigan.

 

DSC00241_zpsdf1c7415.jpg

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The Auto is based off the front/rear wheel speed.

 

As soon as the rear slips under power, the front will kick in and pull it to wherever the wheels are pointed.

 

My understanding is that the auto system applies more power to the front at higher speeds than lower speeds. So it would help with fishtailing some. But if conditions are that sketchy I just use full 4x4.

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The NVG 246 EAU provides 5 modes, Auto 4WD, 4HI, 4LO, 2HI and Neutral. 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 0-5 ft lb 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. The NVG 246 EAU transfer case features a 4 button shift control switch located on the instrument panel. When the ignition key is in the RUN position, the transfer case shift control module monitors the transfer case shift control switch to determine if the driver desires a new mode/range position. At a single press of the transfer case shift control switch, the lamp of the new desired position will begin flashing to inform the driver that the transfer case shift control module has received the request for a new mode/range position. The lamp will continue to flash until all shifting criteria has been met and the new mode/range position has been reached, or has been engaged. Once the new mode/range position is fully active, the switch indicator lamp for the new position will remain ON constantly. 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 both the front and rear propshaft speed sensors. When the vehicle experiences a rear wheel slip condition, 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 encoder motor. This motor rotates the transfer case control actuator lever shaft, applying a clutch pack. This clutch pack 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 propshaft speed sensor matches that of the rear propshaft speed sensor. Torque is ramped down to the front wheels. The process would repeat if rear wheel slip is detected again. The NVG 246 EAU transfer case has the added feature of also providing the driver with 3 manual mode/range positions:

 

*4HI - 4 Wheel Drive high range

*2HI - 2 Wheel Drive high range

*4LO - 4 Wheel Drive low range.

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