What does it take for 4x4 Auto to actually turn on the 4WD?

[Huntsman06]

A fun little question I've had for a while now.

This was the first year I've owned my explorer and the 4x4 auto has always intrigued me. I've been told that it's essentially an AWD vehicle while in 4x4 auto but can change into a more traditional 4x4 whenever it's put into either high or low. I've also heard lots of people complain that their Explorer has a tendency to detect slipping while in 4x4 auto when driving on flat, dry roads. Fortunately, mine doesn't do that. In fact, I drove it all winter through some pretty impressive snow storms (by northern Utah standards) and it NEVER jumped into 4x4 by itself when left in Auto.

Now I did put it in 4x4 high when the weather was really, really bad--so the explorer never really had the chance to do it on its own, but I'm fascinated how much it can take without kicking it into 4x4. Has anyone else ever noticed their explorer never going into 4x4 on its own when left in auto--or if they do does it take extremely rough road conditions? Lastly, I am the 3rd owner and it's 13 years old so it COULD have been brown wired sometime in the past, but I've never bothered to check

 

[Joe in NY]

When you stomp on the gas in snow (Forward or Reverse) and get your wheels spinning pretty good it'll kick in. Like trying to do a drift.

 

[96firephoenix]

The Auto 4x4 uses the ABS sensors to monitor that the wheels are all rotating at the same velocity, so any error codes in your ABS system will disable the Auto 4x4.

One of the big problem points is that it kicks on during low speed turns (i.e. into a parking spot), the wheel on the inside of the turn moves slower than the one on the outside and kicks on the Auto 4x4.

 

[Tech By Trade]

Mine usually kicks in a few times when I'm out ice fishing. Once the rear tires start loosing traction in the snow. I have also had it kick in climbing hills in the valley when we are out deer hunting in the fall and the back starts slipping.

 

[MrPulldown]

If everything is working right and you are driving straight you shouldn't notice when it goes into 4wd.

 

[Joe in NY]

One thing that makes the systems over the years interesting is that my 2002 Explorer does not have the Adavnce Trac / Traction Control. What this means is that I only have 3 speed sensors.

1 - Transmission Output Shaft Speed
2 - Rear Diff Ring Gear Speed
3 - Front Diff Ring Gear Speed

This means that the 4WD and ABS have to rely the very basics as to what the wheels could possibly be doing and attempt to correct it. Explorers with traction control have 4 wheel sensors to know exactly what is going on.

Personally, I love NOT having traction control. 100% power when ever I mash the pedal to the floor. No nanny computer telling me no.

 

[imp]

@Huntsman06
It will often kick in momentarily if only one wheel suddenly slips a bit when first starting from a standstill especially on gravel. Will make a "clunk" sound as the Electronic Clutch engages the front wheels. imp

 

[MrPulldown]

Mine made a very noticeable clunk when 4wd was engaged. Then I switched out the transfer case fluid. Now you don't hardly hear or feel the clunk. it will only do it very softly almost unnoticeable unless you really pay attention and only when you mash on the gas on a snowy/icy start up.

As for traction and stability control nannies. Honing in the dirt is one thing, but your wife sliding out of control, with the kids in the back seat towards on-coming traffic is another.

 

[faberj]

Your question reminded me of one from my wife. We have a 04 which we bought new and at the time she was the main driver. So after driving it for 5 years in the snow and ice of Mn. she asked how do you put it in 4 wheel drive. It's obvious the system works or she never needed it. She now drives a AWD 09 CRV which puts it in AWD on it's own as needed.