How does the AUTO button work in a 4x4 Ford Explorer?

[JamesExplorer97]

So just a few more simple questions, can someone explain to me when my car is in AUTO (the turn knob is pointed on AUTO) am i still in 4 wheel drive or 2 wheel? How does this work?

And if it snows should I leave it in Auto??? Since im assuming it will automatically sense where the power needs to go? It's a 1997 FORD EXPLORER LIMITED 4x4

 

[koda2000]

I believe the AUTO setting uses the vehicles ABS sensors to determine if there is any difference detected in wheel speed. if there is, it automatically engages the front wheels. unless there is slippage the front wheels are not normally engaged in the AUTO mode.

many people don't like this feature, hence "the brown wire mod" to disable it. the only time you are in true 4 wheel drive is when the switch is set to 4X4.

 

[AP9]

As koda2000 said, AUTO normally has just the rear axle engaged, and if the ABS sensors see the rear wheels spinning considerably faster than the fronts, the transfer case clutch will cycle on and off until the speeds are equalized.

AUTO is usually fine for winter, but when I drive through exceptionally deep snow I switch over to 4WD HIGH, which will keep the front driveshaft engaged and spinning at the same speed as the rear. Good for poor or uneven traction conditions; bad for normal on-road driving conditions.

 

[imp]

Aggravating "Auto" Design

In the case where wheels slip suddenly, then stop slipping, then start again, as on loose sand, or packed snow, the rapid "on-off" switching of the transfer case electronic clutch can cause pretty loud, even scary, noises and vibrations, especially if any "play" is to be found in the driveshafts and gearing. Of course, some play is always there.

IMO, the Auto 4X4 design is not really a good solution; it just gives average drivers protection. Personally, I lean more in favor of AWD. Watch me catch flack for that one! imp

 

[Beargap]

So just a few more simple questions, can someone explain to me when my car is in AUTO (the turn knob is pointed on AUTO) am i still in 4 wheel drive or 2 wheel? How does this work?

And if it snows should I leave it in Auto??? Since im assuming it will automatically sense where the power needs to go? It's a 1997 FORD EXPLORER LIMITED 4x4

The Control Trac transfer case uses an electronically activated clutch mechanism (Borg-Warner design, same as used on a Hummer) that engages the power to the font axle by increasing the "on" time something like 60 times a second. Normally it is supplying around 10% of the power to the front driveshaft in the Auto position, but when the speed sensors in the transfer case (not the ABS) report the rear driveshaft is turning faster than the front, it increases the pulse duration in 10% increments until the rear is no faster than the front, then it starts to ramp back down. If it gets to 100% engagement and the rear still seems to be faster, it disconnects and flashes the 4WD indicators as that is not possible, so something is wrong...typically a failed or dirty speed sensor. In the 4WD-Hi and 4WD-Lo positions, the transfer case is locked on 100%, but that means you will get significant driveline binding if you attempt to turn on dry pavement, which is not a good thing. For typical snow conditions, with dry and icy patches on pavement, the Auto position is fine and takes care of everything, but since you actually have to start slipping for the system to shift power, locking the t-case in -Hi or -Lo will give a more sure-footed start as long as you aren't turning.

Incidentally, the later AWD versions from Ford were the same system, without the option to lock the t-case except going down into the system menu. The older versions used a viscous coupling in the t-case which worked like a differential and were fine until you started to slip, and then one wheel spinning could just about stop everything.

 

[SoNic67]

The older versions used a viscous coupling in the t-case which worked like a differential and were fine until you started to slip, and then one wheel spinning could just about stop everything.

You are wrong. One wheel spinning is nothing for AWD.
The central VC would lock up the front to rear on axle speed differences. Combined with Limited Slip rear differential, it basically means that AWD would still move with 3 wheels slipping (2 front and one rear) or, worse case scenario, 2 wheels slipping (both rears).

 

[Beargap]

You are wrong. One wheel spinning is nothing for AWD.
The central VC would lock up the front to rear on axle speed differences. Combined with Limited Slip rear differential, it basically means that AWD would still move with 3 wheels slipping (2 front and one rear) or, worse case scenario, 2 wheels slipping (both rears).

I may be, at that. I've actually never had an AWD system that had a VC. Part of that comment came from seeing a YouTube video "Testing Viscous Coupling" that showed a lot of wheel spin with one wheel off the ground, although admittedly the other axle did turn some.

 

[SoNic67]

It takes a couple seconds to heat up the VC and engage the other axle.
Front diff is open thou.