Auto mode turns on 4x4 mode

[swathdiver]

Hello All,

Recently I can't run in Auto mode without my 2013 Tahoe LTZ (w/only 75k miles) going straight into 4WD, even with no traction loss. I've got to switch to 2WD to unlock 4WD. Not sure if it matters but I removed fuse #9 (ABS, stabilitrack, & traction control) over a year ago, so I wouldn't have to manually turn off these useless functions (IMO) every time I get in my vehicle.
Any help would be much appreciated, thanks.

Johnny, you really need to get a Tech-2 on this and pull up the internal codes and it can also perform diagnostics. If you don't know anyone with one or a similar tool, check out the Tech-2 owner's thread and see if someone lives near you.

 

[91RS]

I'm not going to get into a ******* contest. You're misinterpreting the word variable to mean varying levels of low traction, when the intent is for any range from normal (dry) traction to low traction.

Auto 4wd is designed for situations where you MIGHT encounter bad traction conditions. You're not going to get tire scrub while in Auto, because the front diff is still unpowered. Only when the vehicle detects slippage does it actually engage the front diff. Perfect example is plowed roads where there's a chance you might encounter an unplowed road or drifting/blowing snow.

If you're driving in variable low-traction conditions , then just put in 4hi.

Once again, that isn’t true. You can feel the power going to the front wheels when you accelerate when it is in auto, even at speed. It is sending power up front much more often than when there is low traction. Which is why it should not be used on pavement. I’m not misinterpreting anything you just can’t be wrong so you’re bending the meaning to be what you want.

I’m done, apparently, everyone here is best pals with the engineers and knows exactly what GM designed even though the owners manual says otherwise. Go ahead and run around on auto all the time since you know best. It worked out so well for the OP.

 

[PatDTN]

Just a point to add. AWD vehicles have a differential in the system to allow the front wheels to turn at a different speed from the rears. 4wd vehicles don't have that. In turns the front takes a wider arc than the rears. Not sure how GM handles the difference in automatic 4wd mode except to disengage 4wd when it senses pressure.

 

[intheburbs]

I’m done, apparently, everyone here is best pals with the engineers and knows exactly what GM designed even though the owners manual says otherwise. Go ahead and run around on auto all the time since you know best. It worked out so well for the OP.

Actually, a good friend of mine was on the validation team that tested and validated the 6L transmissions for GMT900. And I have several friends who still work at GM.

No one is saying to run around full time in Auto, you know that, and saying that is just being a jerk.

 

[91RS]

Then let’s get a statement from them that GM designed the system to be used in auto all the time. I’ve never found any documentation from GM that says the system is designed for what you are saying.

None of your posts say not to use Auto 4WD all the time. George is the only one to actually say that. Wjburken said he wouldn’t recommend it after arguing for a few posts that it’s ok to use it on pavement. But you have not said that at all.

 

[intheburbs]

Then let’s get a statement from them that GM designed the system to be used in auto all the time. I’ve never found any documentation from GM that says the system is designed for what you are saying.

None of your posts say not to use Auto 4WD all the time. George is the only one to actually say that. Wjburken said he wouldn’t recommend it after arguing for a few posts that it’s ok to use it on pavement. But you have not said that at all.

Because it seems to me to be patently, ridiculously obvious that people drive in 2 most of the time.

You use Auto in situations where you think you might encounter low-traction situations. Rain, blowing/drifting snow, etc.

Again, driving on back roads in winter, mostly plowed and dry, but with the potential for blowing/drifting snow? That's exactly the situation for which Auto was devised. Personally, I probably use Auto at most once or twice a year.

 

[tungsten]

Full on winter roads here last week,good 2" of snow.I tried auto,you could feel it going in and out.Was rather annoying.I normally just go back and forth 2wd-4wd pending on speed.

 

[George B]

I found this nugget...

Transfer Case - NVG 246-NPS (Two Speed Automatic)

Transfer Case General Operation

The New Venture Gear model NVG 246 RPO NP8 transfer case is a two speed automatic, active, transfer
case. 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 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

The driver may choose to select any of these mode/range positions while driving the vehicle. However,
the transfer case will not allow a shift into or out of 4LO unless the following criteria has been met:

• The engine is running.
• The automatic transmission is in Neutral.
• The vehicle speed is below 5 km/h (3 mph).

This transfer case also has a Neutral position. A shift to the Neutral position allows the vehicle to be
towed without rotating the transmission output shaft. Neutral position may be obtained only if the following
criteria has been met:

• The engine is running.
• The automatic transmission is in Neutral.
• The vehicle speed is below 5 km/h (3 mph).
• The transfer case is in 2HI mode.

Once these conditions have been met, press and hold both the 2HI and 4LO buttons for 10 seconds.
When the system completes the shift to neutral, the red neutral lamp will illuminate.

The NVG 246 EAU case halves are high-pressure die-cast magnesium. Ball bearings support the input
shaft, the front output shaft, and the rear output shaft. A thrust bearing is located inside of the input shaft
gear to support the front of the rear output shaft. The transfer case requires Auto Trac® II Fluid
GM P/N 12378508 (Canadian P/N 10953626) which is blue in color. The fluid is designed for smooth
clutch application. An oil pump, driven by the rear output shaft, pumps the fluid through the rear output
shaft oil gallery to the clutch and bearings.

There are two versions of the NVG 246 EAU, which depend on the transmission applications and vehicle
applications. If the vehicle is equipped with a transmission RPO M30, the transmission splines in the input
gear will have 27 teeth. With this application the planetary carrier assembly will have 3 pinion gears. If the
vehicle is equipped with transmission RPO MT1 or MN8, the transmission splines in the input gear will
have 32 teeth. The planetary carrier assembly on this application will have 6 pinion gears.


You drive as fast as you want in 4Auto. Limit 4LO to about 35-40 MPH as 4-5,000 rpms is the critical speed of the driveshafts.

 

[George B]

Start at 10:10 of this video for an explanation of how the Auto mode works.

For the record I personally wouldn't have any worry running in Auto mode for an extended period of time and I doubt there would be any damage to any of the components of the system. This whole argument started with the statement that running in auto would ruin the front differential with which I do not agree.

 

[George B]

Thank you gentlemen...best regards, Captain Obvious

So, was it the fuse?