4 wheel drive auto mode

4wd auto engages the front diff and actuates the t case depending on driving conditions

Conditions it's enabled: Straight steering wheel or if it sees rear wheel slip

Conditions it's disabled: Low speed maneuvers where there is no rear wheel slip, or when the steering wheel angle exceeds a given amount.

Spacido said:

That said, I admit that you really have to do it on purpose to lose control with the Tahoe. It is quite stable, even in the rain.

In the GM documentation, there is really no explanation about the automatic mode and it's true that I like to understand how it all works.

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Page 2-25 of the 2001 Suburban/Tahoe owner's manual.

Of course the best option is driver's skill. Knowing how to drive a vehicle in a controlled 'out of control' manner is much safer than relying on a system that may or may not work when called upon. My tahoe has the auto mode but as you can probably guess, I've never used it.

offjaqued said:

Of course the best option is driver's skill. Knowing how to drive a vehicle in a controlled 'out of control' manner is much safer than relying on a system that may or may not work when called upon. My tahoe has the auto mode but as you can probably guess, I've never used it.

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Not sure that's fair to say

when in AUTO the front diff and cv axles are engaged. Try it at home jack up one side and in 2hi spin the wheel. In the later transfer case (like my 06) the front drive shaft will not spin. Put in in Auto the front shaft will spin, but it is not activated by the transfer case until it sees a difference in RPM between the front and rear wheels via the vehicle speed sensor. Obviously, if you switch to 4hi, you will no longer be able to spin the tire because it is locked by the transfer case. The reason you hear and feel a bind in auto is because the front diff and gears are turning and ready to give power at the command of the transfer case. My 06 Yukon as well and my 2018 Sierra have made noise in auto since new. Auto should not be used if full time 4wd is safe to use. the constant clutch slipping of the auto engaging and diengaging will wear the clutches out on the transfer case over time.

rjr said:

While on the subject of the A4WD, on my 2015 Yukon, I find that when in auto, I hear a varying whine at low speeds. Sort of like a tire with an out-of-round thread [which it isn't]. Dealer says this is normal? Didn't do this when new; now 52,000 miles. Is this common?

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rjr - I know this is an old post, but not sure if you found an answer to your question about noise. I have a 2018 Denali and mine sounds the same when I engage 4-wheel Auto. I only have 13,000 miles, but just started noticing it. Although that doesn't mean it wasn't there before since I mostly engage it during winter mix type conditions which would mask the noise. Actually I started searching the forum today about this very thing.

Maize, I have never gotten an answer. Hard to believe that GM can't produce a quiet drive system. It was quiet when new, so there has to be some factor that changes with wear.

Mine's quiet but it has a new front diff. Would type out more but I'm walking out the door

rjr said:

Maize, I have never gotten an answer. Hard to believe that GM can't produce a quiet drive system. It was quiet when new, so there has to be some factor that changes with wear.

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Mine has gotten noisier with age. Added a little more fluid to it and no change. Works fine, just noisy. It's got to be a bearing, there's a whomp whomp sound below 30 mph and a longer rythmic sound that's noticeable around 35-45 mph, before wind noise drowns it out. Boots are good, no leaks, don't really want to take it apart right now and look around either.