4 wheel drive auto mode

[mikeyss]

The motor engages the front axle. In mine, I noticed in auto, 4HI and 4LO, that motor has the front axle locked in. In 2HI, the front wheels were not locked in

 

[Fless]

The diff actuator should not be engaging when in Auto and standing still (no wheel slippage). Does your drivetrain bind on tight turns in Auto? It shouldn't.

 

[Spacido]

I did a test in auto mode with the wheels right in the wet grass and we can hear the front axle snap and make the vehicle go forward so everything is working properly.

But, turning right angle, for example, without skating the rear wheels, I feel a big resistance in the steering wheel and the front wheels that slide as if I was 4WD

 

[Fless]

You could disconnect the electrical connector from the front diff actuator and try it. If it still binds with the actuator disconnected, I'd suspect half shaft CV joints or a diff problem. Does the diff fluid look okay and filled?

Or maybe a hub. Does it do it on a left turn, or only a right turn? If only on a right turn, concentrate on the left side of the frontend. Not sure if the sway bar end links would cause this effect but worthwhile to make sure they're in good shape and tight.

 

[Spacido]

Yes, when I bought my truck in October 2018, I drained all the fluids, especially the automatic gearbox and the TC. Because in France, mechanics put everything and anything because they do not control all that.

And I was right, because it was not Autotrack II in the TC

 

[rjr]

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?

 

[OneofFew]

I may not understand the auto 4x4 system well, but waiting for wheel slippage to lock in the front hubs- what could go wrong? LOL!
I would not expect auto 4x4 to be reliable and would leave it in 2hi mode until you actually need 4x4.

 

[Fless]

Auto is really for varying traction conditions, like a mix of dry and wet pavement. In full on snow or wet, 4x4 is best. Auto will engage parts of the drivetrain in and out as needed and theoretically save wear and tear. Don't use 4x4 on dry pavement, you'll get drivetrain binding and that can cause excessive wear and tear.

I wouldn't say that Auto is unreliable; one just needs to expect that it will take the front diff actuator a second or two to engage 4x4. Sometimes that's acceptable, and other times not.

 

[OneofFew]

Let's face it, it's a useless gimmick. If you go around a wet turn and the rear kicks out a but you counter-steer and are well in control...until the 4x4 kicks in and puts you in the ditch because you could not gradually recover from the slide, but catch traction unexpectedly.

 

[Spacido]

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.