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Very interesting thread here guys. Allow me to add a few points.
1) MudRuts is absolutely the most capable AWD mode. Slippery is close but MudRuts is best suited for challenging/slippery surfaces and it does disable TC to allow more wheelspin (within reason).
2) Even if the software could be cheated into a locked mode, I wouldn't recommend this. The t-case is not normally locked up for extended periods of time and doing so could cause it to fail.
3) Don't feel like you got a cheap & cheerful AWD system just because it goes in a van. The same system goes into the RWD Ford Explorer, too.

If you get the AWD Temporarily Disabled message, it will clear after a few moments and give you AWD back. You're correct that it's detecting heat in the system and it shuts down to protect itself. If you somehow bypass that and smoke the clutch, the AWD would be shot and you'd have to replace the whole t-case. Temporarily Disabled is just that: temporary. It's there to save you having to replace expensive parts.

Any AWD message that's not an actual Diagnostic Code (like something has actually broken) can be cleared with a key cycle. Remember that will put you back in Normal mode so if you're stuck or getting stuck, put it back in MudRuts after you restart.

I do not like how the Drive Modes require repeated button pushes to pick the mode. For example you could accidentally go one past MudRut and end up in TowHaul. MudRut is the most aggressive mode but TowHaul is the least aggressive, so you're more likely to get stuck.

Ok so all that said, the system should not have shut down as easily as it sounds like it did. Questions:
1) Do you have much weight in the van?
1) Did you have the steering wheel turned while you were trying to get unstuck?

Technically neither of these things should matter much if you were actually in MudRuts mode. Like any AWD system, it reduces torque when the front wheels are turned (this prevents crow-hop on hard surfaces). If you're stuck or getting stuck, keep the wheels as straight as possible. The system adds more torque if the wheels actually do slip, but on mud or ice sometimes slipping means the surface is already glazed over and you've lost most of the grip from those back tires. And yeah, the stock tires are not intended for - or very good in - mud.

This is getting long so apologies but I just want to add: don't feel like the system has failed you or lose too much confidence. I wonder if there might have been something going on during that particular drive. The system re-learns and heals itself every drive cycle so the van is probably back up to 100% by now and you might want to try that grade again (make absolutely sure you're in MudRuts and have a truck buddy along just in case!) Any questions message me.
 

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That seems really odd for the system to be shutting down on just a dirt road. I can see traction control turning off to save the brakes from excessive heat but the AWD system? Are you pushing it really hard like pre-running in order to get it to turn off? Does it always come back on after a few minutes?
I agree, it should be able to run all day on those kinds of surfaces. Do you have four same/similar tires on the van? Is the message "AWD Off" or "AWD temporarily disabled"?

The temporarily disabled is generally due to heat being detected in various parts of the system, although there are no actual sensors, it's all analytical heat assessment. If there is a ton of noise on the wheel speed inputs due to traveling rapidly on rough/irregular surfaces, it's possible to gradually ratchet up the calculated temperatures, but this is pretty unlikely and difficult to actually achieve.
 

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OK< so there is a servo operated clutch in the transfer case. But what is in the PTU? Is it a wee little differential? Sprag clutch? Black magic? Magic beans?
Which component are you referring to as the "PTU"?

Power flows from the engine straight back through the trans and t-case. The t-case sends torque primarily to the rear axle while syphoning some amount off to the front axle, depending on the level of engagement of the motor-actuated clutch pack. You're correct that it uses a chain to transfer torque between its two shafts. Finally, the hypoid gears in the differentials turn the torque 90 degrees out to the wheels.

There is no Power Takeoff Unit in this system or any conventional RWD/longitudinal 4x4 system with a t-case. FWD AWD typically uses a PTU to turn torque 90 degrees from the transverse mounted engine/transaxle back to the rear wheels.

No magic beans in the hardware, they're all in the software/controls system.
 

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I am told the small box of gears in the front axle is a PTU. Is it a differential then? It is very small and holds a tiny amount of oil.
Yep, just a run-of-the-mill open diff. Nothing particularly interesting in there. AWD sends torque in, differential sends torque out.

FWIW, the only way to bias torque across the front axle or prevent slip up front is by traction control. So if front end grip is lacking, blame the tires or the brakes, not the AWD :)
 

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No issues with my AWD, but I can't see the open diff in those PTU units. There are a few videos of them being opened, I don't see an open diff.
Ah, make sure these aren't European Transits in the videos. They've had AWD for years, but the Euro AWD hardware is very different from what goes into the North American AWD Transits. Theirs is a hydraulic system and it's housed in the front axle so if you're seeing some interesting components in there, it may be a European vehicle/video and it probably doesn't match what's in your van.

I don’t plan on rough off roading. Got AWD for extra traction like mountain
travel in winter for some snow activities, slippery dry summer Forrest roads
to trailheads. So If I go up a long dry Forrest road with some good grades
but taking it easy 10/20 miles hour one may still encounter AWD shut down??
This is exactly the type of terrain/surfaces the AWD system is designed for. You will be fine.
Also, see below...

I’ve taken my van on long dirt roads and off-road trails and no shut downs yet for me. (Mud/ruts mode). I’ve only heard of a couple vans having this problem
I agree with @ArgonautVans, I think the vans experiencing these issues off road (even in relatively tame terrain) may have some other issue going on. There are things that can actually shut down AWD, like using a smaller spare tire, having mismatched axle ratios, or especially, having a faulted ABS wheel speed sensor.

I've driven a lot of miles in AWD Transits in all kinds of terrains, from stuff they're intended to drive in to stuff they are most definitely not, and the AWD Off message is very unusual (a small spare tire will trigger it, but that's by design). The system as a whole is pretty capable - your ground clearance, departure angle, and tires will become a limiting factor before the t-case gives you any issues off road.

Hopefully this helps with your decision / questions. Feel free to reach out to me via DM with any specific questions.
 

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Fwiw, as an F150 driver, I was stuck once in a rut but could not get out. The 4x4 low would disengage whenever wheel spin hit a threshold. And the power was never adequately transferred to the opposite wheels.
...
This sounds like it was an F150 with a "4A" setting for its t-case?

If so, then yes it is possible to overpower the clutches in certain situations. Using 4L does not help. If the t-case is healthy it will not happen very often. Technically it's not a wheel spin threshold, if you're spinning the rear wheels and not the front, that slip is all going across the clutch. Like any clutch it doesn't like heat so it's designed to open up to keep from ruining itself and having to replace the whole t-case.
This is an unfortunate trade off of the nice smooth fulltime AWD systems. A locking 4x4 t-case would not be susceptible to that, but it also has terrible road manners and is clunky driving on road in rain or light snow, stuff like that, which is where AWD excels.

I will say, if you are traction limited (like spinning tires in a muddy rut) then adding torque by using 4L is not the answer. 4L is not an "extra-capable" 4x4 mode to use when AWD or 4H are not working. It has its places, but primarily it's for very low speed, technical creeping or very fine throttle control, like places where you need to keep your engine speed up in the powerband but the resulting vehicle speed would be too high in normal/high range. The engine always makes the same amount of torque, which is going to be sufficient to power the vehicle and probably slip the tires almost anywhere. 4L just takes that engine torque and multiplies it by the ratio in the t-case, meaning you have even more torque available to slip the tires and get stuck.
 
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