4H / 4A / 2H

[wannabeMtb]

Noob expedition owner. Just want to make sure I am not doing anything wrong w.r.t 4WD / AWD

First question:

My 2022 expedition makes some weird sounds from the transmission when I am running on 4H at slow speeds. Is this normal ? I had just returned from a snow mountain trip to Tahoe (360 miles round tip). I had switched from 2H to 4H when I started encountering snow going uphill on the mountain. I left it at 4H even while coming back and back to regular roads (Bay Area). And now when driving slow on residential roads in bay area, the 4H is making weird sounds and there are a few jerky movements.

Second question:

Want to confirm that my following understanding is correct
4H : Use this to force vehicle to run power to all 4 wheels ALL the time
4A : Vehicle computer decides whether to power 2 wheels or 4 wheels. Vehicle computer may decide to run at 2 wheel drive when road conditions allow it.
4L : To be used only at very low speeds and to be used for say pulling the vehicle out of a ditch or when stuck on snow/sand

 

[LokiWolf]

2 Things:

1) Expedition does not have AWD, it has 4A. They are not the same.
2) You should NEVER run 4H/4L in anything except for low traction situations, like driving in actual snow. More below.

4WD, in our case 4H, and 4L will cause binding, because all the wheels should be going the same speed(Yes - oversimplified, because with 2 open Diffs it should be 2 - 1 front and 1 rear). In 4H, both the front and rear Driveshaft is engaged and power is going down both all the time. On dry pavement or any surface with good traction this will cause binding, clunking, chattering, and other things similar.

4A(4WD Auto), is almost like AWD, except the decision about power to the front wheels is made by the computer using the TOD(Torque on Demand) Center diff. If it senses traction loss in the rear, power is sent forward. The front driveshaft is already in play. If driving along, on Dry pavement, engaged 4A, and you should feel a difference, because the front spinning mass is now engaged, just not getting any of the drive power.

Basically when things start to get slippery use 4A, then when it gets serious use 4H. OR, you could use the modes and let the computer do what it does REALLY well. The Snow mode works well.

Only advantage to 4H in snow conditions over 4A is Engine braking. In slippery downhill situations it can be helpful.

 

[wannabeMtb]

2 Things:

1) Expedition does not have AWD, it has 4A. They are not the same.
2) You should NEVER run 4H/4L in anything except for low traction situations, like driving in actual snow. More below.

4WD, in our case 4H, and 4L will cause binding, because all the wheels should be going the same speed(Yes - oversimplified, because with 2 open Diffs it should be 2 - 1 front and 1 rear). In 4H, both the front and rear Driveshaft is engaged and power is going down both all the time. On dry pavement or any surface with good traction this will cause binding, clunking, chattering, and other things similar.

4A(4WD Auto), is almost like AWD, except the decision about power to the front wheels is made by the computer using the TOD(Torque on Demand) Center diff. If it senses traction loss in the rear, power is sent forward. The front driveshaft is already in play. If driving along, on Dry pavement, engaged 4A, and you should feel a difference, because the front spinning mass is now engaged, just not getting any of the drive power.

Basically when things start to get slippery use 4A, then when it gets serious use 4H. OR, you could use the modes and let the computer do what it does REALLY well. The Snow mode works well.

Only advantage to 4H in snow conditions over 4A is Engine braking. In slippery downhill situations it can be helpful.

Thank you for the detailed reply !

So is it ok to leave it at 4A all the time in suburban driving if I am ok with any loss in fuel economy ?

 

[zak99b5]

I'd be more worried about any damage to the transfer case that's making the sound.

 

[LokiWolf]

Thank you for the detailed reply !

So is it ok to leave it at 4A all the time in suburban driving if I am ok with any loss in fuel economy ?

Yes, Many do. Personally I was taught how to drive on RWD overpowered vehicles, so I prefer the handling characteristics and behavior that brings. In dry situations, my recommendation is to leave it in 2WD. Unless you are leaving the light at full throttle every time, 2WD and the ELSD will handle it just fine. Sport actually engages 4A for that exact reason, for traction under hard acceleration.

 

[LokiWolf]

I'd be more worried about any damage to the transfer case that's making the sound.

Yeah, not a bad point. @wannabeMtb Does it make any weird sounds now that you have turned 4H off and on dry roads?

 

[Rob6805]

I told my wife to just use the drive modes. Put it in Snow mode when it's snowing. The only thing I do not like is that the drive mode reverts back to normal on a key cycle.

 

[LokiWolf]

I told my wife to just use the drive modes. Put it in Snow mode when it's snowing. The only thing I do not like is that the drive mode reverts back to normal on a key cycle.

I actually kinda like it. I come home after driving the Expedition, I had it in Sport cause I was having fun, and when the wife drives it the next day it is back to Normal...

 

[SyndicateZ]

I have HD tow with the 3.73 eLSD. I dont even have a 4H. I wouldnt ever use it anyways. 4A is the choice in snowy, icy roads.

 

[wannabeMtb]

Yeah, not a bad point. @wannabeMtb Does it make any weird sounds now that you have turned 4H off and on dry roads?

No it doesn't thankfully

 

[rd618]

I have HD tow with the 3.73 eLSD. I dont even have a 4H. I wouldnt ever use it anyways. 4A is the choice in snowy, icy roads.

The 2022 models have a 4H option, was not available in previous year Gen4's.

Drive modes as others suggest is the best option for 95% of drivers.
Along with good tires.

 

[zak99b5]

I noticed that on my 2020, if I had it in snow mode on the previous drive, on next start it's back to normal (as expected)--but it's still in 4A. I manually have to select 2H to revert back.

 

[m3olsen]

Unless you are leaving the light at full throttle every time, 2WD and the ELSD will handle it just fine. Sport actually engages 4A for that exact reason, for traction under hard acceleration.

Has anybody played around with running Sport Mode and keeping the Power Distribution display up? I've done this, and miles later, on dry roads, driving lightly, my display shows power still going to the front wheels (4A enabled by Sport Mode). Yet I've never experienced any clunking, so I do believe the TOD must be working.

 

[2020-MAX-Limited]

Has anybody played around with running Sport Mode and keeping the Power Distribution display up? I've done this, and miles later, on dry roads, driving lightly, my display shows power still going to the front wheels (4A enabled by Sport Mode). Yet I've never experienced any clunking, so I do believe the TOD must be working.

There's another thread that reports the same thing--Sport Mode drives all 4 wheels. Curious if the 4A light switches ON when Sport Mode is selected? I would assume so.

 

[2020-MAX-Limited]

I noticed that on my 2020, if I had it in snow mode on the previous drive, on next start it's back to normal (as expected)--but it's still in 4A. I manually have to select 2H to revert back.

I concur. I saw the same thing. 4A stays lit, but Drive Mode is back to Normal. Have to manually rotate the dial to get back to Grass/Gravel/Snow mode. Of course, then I always rotate the knob in the wrong direction and have to correct back the other way.

 

[m3olsen]

There's another thread that reports the same thing--Sport Mode drives all 4 wheels. Curious if the 4A light switches ON when Sport Mode is selected? I would assume so.

Confirming that 4A stays on when you switch back to Normal - you need to select 2A manually. The Power Distribution visual display is what seemed odd to me. I don't have a pic to post currently, but it gives a visual as if you were looking down on the vehicle, and all 4 wheels are displayed as stacked bar graphs. The bars grow taller as you apply more acceleration. My surprise is that the display shows power to all 4 wheels when it shouldn't need to.

 

[Soliyou]

When in 4A, the front hubs engage, and transfer case engages the front drive shaft from stop up to a certain speed, this means you are in 4wd.

Above a certain speed, the transfer case disengages the front drive shaft (but front hubs are still engaged) until (a) slip occurs or (b) you floor it and it downshifts, then it send power to the front again.

This operation is shown clearly in the power distribution screen and when power is sent to the front axle you can feel the drivetrain vibration. In summary, the power distribution screen is correct.

 

[LokiWolf]

When in 4A, the front hubs engage, and transfer case engages the front drive shaft from stop up to a certain speed, this means you are in 4wd.

Above a certain speed, the transfer case disengages the front drive shaft (but front hubs are still engaged) until (a) slip occurs or (b) you floor it and it downshifts, then it send power to the front again.

This operation is shown clearly in the power distribution screen and when power is sent to the front axle you can feel the drivetrain vibration. In summary, the power distribution screen is correct.

This! Much better explanation than I did in the other thread.

40MPH is the lowest I have seen the front go to zero in 4A, very light throttle.

It actually never really engages or disengages the front drive shaft, because the Center Diff in these is not on off, it is TOD(Torque on Demand), and clutch based. It can go from Zero to 50% and any in between at the demand of the computer.

 

[LokiWolf]

As far as 4A staying on…and so forth between mode changes and power cycles. That is well documented.

If you are say in Sport, and turn the Truck off. If you start it back up an hour later, you will be in Normal, but with 4A engaged.

If you are in Sport, and turn it back Normal before you turn the Truck off, it will go back to 2H. You will be in Normal when you start back up.

If you do the first scenario, and want to get back to Normal without 4A, you do not need to change back to the mode you were in before, and switch back, just merely hit the 2H button. The mode has already been reset to Normal by the new start up, you just need to return to 2H.

 

[Calidad]

So all awd or 4wh will bind and have noise especially on surfaces that aren’t slippery. I wouldn’t run it in anything other than 2wh when on clear pavement. Even wet pavement ideally 2wh only.

Having said that my stock OEM tires even with 15,000 on them were horrendous even on wet bay area highways. I couldn’t stand them anymore and got BFG Trail Terrains which are a hybrid A/T 3peak rated tire for SUVs. The difference was massive totally different vehicle. Even the Tahoe trips on the typical packed icy trash secondary roads which demanded snow mode 4hi just to get around with lots of sliding. The new tires I could go everywhere in South Lake in 2wh with virtually zero sliding. Massive difference can’t even compare the two tires.

I only run 4whl modes when traction is an issue for 2wh. So Tahoe trips snow mode goes on at the chain control check and off the moment roads are generally clear. These 4whl systems use clutches to drive power to tires with traction and using them when road surfaces are not an issue just creates heat and excess wear on the system.

Most definitely treat the stock tires as complete trash especially for Tahoe conditions. Even in 4whl the stock tires severely hampered the expedition vs new 3peak tires we’re better in 2wh than the OEM’s were in 4whl..
My neighbor just got a Expedition and I warned him about the stock tires. He’s a car guy made a week long trip family snow trip. He got back and told me yep tires are terrible and on the list to replace. He said even snowy roads he struggled to get the Expedition to move a few time. Same issue I had in Tahoe with my old stock tires. The same places my old tires were just not able to get it done in 4whl my new tires could easily do in 2whl. Tires are a huge deal even with 4x4 systems.