If I'm not mistaken there were no AWD Expeditions.
4Auto is 2WD unless slippage is experienced in the rear axle. If slippage, the transfer case engages the front axle.
4Hi is locked into 4WD for sand, snow mud etc.
4Lo is for high ration pulling, getting out of a sand pit etc.
If you leave it in 4Auto it's in 2wd unless the system encounters a condition to engage the front axle. On a dry road without nailing the throttle, you'd never engage 4wd in 4auto.
I know enough to be dangerous, no expert ... barely head above water on this and many other topics.
BUT there is a WIKI page on this ...
https://en.wikipedia.org/wiki/ControlTrac#The_Modes
and this quote from the WIKI says the opposite
of what you typed about 4Auto above?
So I disagree. if I'm wrong , forgive me ...
Auto mode was featured on both Explorer and Expedition and allows for all-
weather, full-time four-wheel drive capability on pavement as needed. In Auto mode, the engine’s torque is normally routed to the rear drive wheels. A misconception about the system is that it continuously shifts into and out of four-wheel drive as needed. This is not true, for when
Auto mode is selected, the front axle hubs are permanently engaged, locking them to the front axle shafts, front differential, and front
drive shaft. This is so the front drive shaft always rotates (turns) when the vehicle is being driven at
speed. The computer control system needs the front drive shaft to turn, so that it can monitor and compare the rotational speed of both the front and rear drive shafts. If the rear drive shaft starts to turn faster than the front, the system interprets that (along with input from other sensors) as traction loss. When traction loss is detected, torque is sent forward to the front differential in 10 percent increments, via the center multi-disc clutch. As it does so,
intelligent control software allows the center multi-disc clutch to behave like a geared center differential, such that "driveline binding" and "torque windup" do not occur. The transfer of torque is done in
secrecy, virtually undetectable by the occupants of the vehicle.
In the early 2000s,
ControlTrac was updated and introduced in 2002 with more advanced software programming, building on the system’s
artificial intelligence.
[8] The four-wheel drive system's updated artificial intelligence allowed the system to
predict traction loss before it happened, so that torque can be transferred before it was needed.
[7][8] This improvement meant the system could operate more like other "always-on" full-time four-wheel drive systems as it no longer had to "wait" for traction loss to take action.
[8] Another improvement was front-to-rear "
torque biasing" capability in Auto mode.
ControlTrac's intelligent multi-disc differential could now send all 100 percent of the engine’s torque forward,
biasing it to the front differential if severe traction loss was anticipated, predicted, or detected.
[8]
