Expedition 2019 Platinum 4A mode really "auto" or is it actually 4H?

xmountaineer said:

I’ve only owned my 19 max (with the hd tow package) for about a month but so far I must say that I am not overly impressed with 4A. I live on a gravel road and my driveway is also gravel, long, somewhat steep in sections and has one big turn going up the hill. This section is definitely not steep. I engage the gravel/grass/snow mode before getting on my driveway. When I go around this turn about half the time the traction control light comes on and the power gets cut way down. I’m going no more than 10mph. It never feels like the front tires grab. There should be no way that the traction control light should come on in this situation if 4wd was truly working. At minimum the elsd should kick on, right?….and front tires should pull me up. Next time I’m going to put the power distribution graphic on the display and see what happens. I engaged the elocker one time and won’t ever do that again going around that turn, it seemed like it struggled even more, likely because of the turn. I can zip right up my driveway with a front wheel or awd vehicle with zero traction issues.

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The locker is for going in a straight line.

I think there may be a terminology issue, here. (Caveat, I don’t have 4H).

I think people are saying that 4 wheel drive is ‘locked in’ in 4A because the front differential is engaged, where in other vehicles, for 4A (auto) it would only engage when needed.

However, in 4A, just because it’s engaged, does not mean power is being applied. The net effect, if no power is applied, is 2 wheel drive, regardless of the front differential turning. The transfer case (or however they split the power) can now smoothly distribute power.

What this means is that they can respond to power distribution requirements prior to detection of slipping, for example, which many (?) 4A systems do.

The example of highway driving in 4A sport. If you are in sport mode under these conditions, it is reasonably expected by the system that the vehicle will be driven in a sporty manner - hard cornering, acceleration and braking. To preempt a chance of the wheels slipping, instead of applying total power to 2 wheels, it distributes that power to 4 wheels, each of the rear wheels seeing less power (torque) for the same conditions would mean less likely to slip.

Conversely, in a 4H condition (my experience with other SUVs without 4A) power is distributed evenly, or fixed (e.g 40/60 split) regardless of accelerating or braking.

The question would be, why would you have a variable distribution of power, and not just split it evenly always? While I cannot answer that directly, I’d retort with a question myself: why do large SUVs and trucks have the rear as primary drive?

This is my understanding from an engineering perspective. YMMV.

sjwhiteley said:

The question would be, why would you have a variable distribution of power, and not just split it evenly always? While I cannot answer that directly, I’d retort with a question myself: why do large SUVs and trucks have the rear as primary drive?

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I’m not an expert on this but there are tons of videos and articles on it.
Short answer is AWD which bias to one axle or two wheels is typically preferred for most on road driving. (Think Subaru or Audi). True 4WD (f-150/expy) is superior for off road or more intense needs. Due to customization and consistency in operation. But does not offer the same on road characteristics.

AWD isn’t bad. It’s far easier and smarter on road, it’s also seamless.
My 2 cents is that 4A was designed as a way for people to be lazy. Historically You had to engage 4H to get unstuck, then you drive like normal in 2H.
Putting driveline power to the 4 wheels only helps with “going”, very little with cornering, and none with stopping.

Ford technology has been similar for many years. I my 2002 Explorer did not have 2H available. 4Auto was for "normal" driving. 4High or 4Low were available.

-- Chuck

sjwhiteley said:

I think there may be a terminology issue, here. (Caveat, I don’t have 4H).

I think people are saying that 4 wheel drive is ‘locked in’ in 4A because the front differential is engaged, where in other vehicles, for 4A (auto) it would only engage when needed.

However, in 4A, just because it’s engaged, does not mean power is being applied. The net effect, if no power is applied, is 2 wheel drive, regardless of the front differential turning. The transfer case (or however they split the power) can now smoothly distribute power.

What this means is that they can respond to power distribution requirements prior to detection of slipping, for example, which many (?) 4A systems do.

The example of highway driving in 4A sport. If you are in sport mode under these conditions, it is reasonably expected by the system that the vehicle will be driven in a sporty manner - hard cornering, acceleration and braking. To preempt a chance of the wheels slipping, instead of applying total power to 2 wheels, it distributes that power to 4 wheels, each of the rear wheels seeing less power (torque) for the same conditions would mean less likely to slip.

Conversely, in a 4H condition (my experience with other SUVs without 4A) power is distributed evenly, or fixed (e.g 40/60 split) regardless of accelerating or braking.

The question would be, why would you have a variable distribution of power, and not just split it evenly always? While I cannot answer that directly, I’d retort with a question myself: why do large SUVs and trucks have the rear as primary drive?

This is my understanding from an engineering perspective. YMMV.

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You would want variable power on each wheel when road conditions like light snow or slick rain could have different traction levels on each wheel. You would want to apply appropriate power to each wheel independently. If one wheel was in the dry and the other in the wet you would not want equal power applied.

4A is the soccer Mom mode but also works for everyone when conditions are on the edge. Downside is it puts more wear on the auto clutches. In some cases like sand, this confuses the computer since wheels will be spinning and some not. Sand is all about momentum and all the wheels going regardless if they need power or not. AND the big reason for 4H is full control from the driver.

I had a Corvette I raced in SCCA and sometimes I would forget to turn off the traction control and stability control (where it applies the brake to each wheel independently to avoid sliding) and it was so slow and intrusive.

I am new here, and normally just read on various forums but never post. I have a 2023 Expedition on order, but haven‘t found specific detail on Expedition‘s center transfer case. I’ll post my thoughts, and please correct me if I’m wrong.

Simply put, 4A is for on-road and 4H is for off-road. 4H can also be used briefly when driving in a straight line (i.e. pulling a boat out of the water), but it should not be used on a surface with good traction.

In 4H (or 4L) the transfer case locks the front and rear drive shafts, so they spin the same speed. This is helpful in keeping momentum off road, and there’s no real issues. Your speeds are lower, and by definition your road has some give to it.

The downside of 4H comes into play on a surface with good or even “okay” traction, particularly when turning. During a turn, all 4 tires are taking a different path and therefore moving at different speeds. This is where 4H can cause driveline binding and stress. All 4 tires cannot spin at different speeds, so one tire “wins”, and another one has to hop or skid.

4A is an all wheel drive mode using a clutch pack to distribute power to the front axle as needed (not sure what the bias is on this truck though). This allows the driveshafts to both get some percent of the power, but also spin at different speeds. When you take a corner, whether or not you have great traction, there won’t be any wheel hop.

4A is very useful in snowy environments where conditions may change from road to road. I live in Colorado, and it’s common to have snow on a north facing road or in tree cover, but then when the road turns and hits the sun, it can be bone try.

That’s my 2 cents anyway, not that anyone asked . If any has details about the center transfer case/differential, I’d love to hear it. I also have a Bronco on order, which borrows from the F150 Raptor style transfer case. I’m assuming the Expy is the same, since it also can support 4A and 4H, but would love to hear any specifics.

Here's a video showing how the transfer case works. Note that the most you can get is 50% front/50% rear. But it's infinitely variable from 0% - 50% front torque. Of course that's when the software comes into play - how they decide how much to put on the front wheels is not easily determined...

My dogs and I just watched the animated video. None of us understood how it works but all of us accept that it does.

Use of 4H or 4L on a surface with high traction will result in axle/driveshaft windup and a large BANG will alert you to this fact as a tire breaks traction. For me this makes 4A especially valuable on suspect surfaces.

-- Chuck

This thread is kind of making ask when I'd ever want to drive in 4H or 4L. What's "off road"? I see the Broncos with state ORV stickers, so I imagine they're going somewhere fun.

I've put a previous Expedition into 4L once to pull my trailer out of a muddy campsite. And then I panicked afterwards because I had no idea how to get it back out of 4L (spoiler: neutral, not park).

Thanks to this thread I've learned that we have things called "ORV parks" here in Michigan. That might be kind of fun.