Sponsored

2H vs 4H

jeepoch

Well-Known Member
First Name
Jay
Joined
Nov 13, 2019
Threads
1
Messages
951
Reaction score
2,687
Location
Longmont, CO
Vehicle(s)
2019 JL Wrangler Sport S 3.6L Auto 2 door, 2.5" lift, 35s
"ESC On" is the default operating mode when the vehicle is running. The driver may disable it manually using the Partial Off or Full Off features, which are exclusively accessed via the ESC button itself.

A full explanation of the ESC system and how it works is evident beginning on, for example, p. 152 of the 2020 Owner's Manual. It is not stated, there or elsewhere, that the act of shifting in and out of 4WD Low will have any effect on the functioning of the ESC system. If there's proof that this does in fact occur, we'll be happy to review it here.
Jeep Wrangler JL 2H vs 4H Screenshot_20201210-193617


James,

In the highlighted WARNING section, first bullet:
ESC "Full Off" mode is intended for off-highway or off-road only.

Also whenever I drop into 4Lo my 'ESC Off' indicator light comes on.

Jay
Sponsored

 

JayJay

Well-Known Member
First Name
Johnny
Joined
Feb 13, 2020
Threads
0
Messages
1,406
Reaction score
4,664
Location
North Georgia
Vehicle(s)
'20 JLR
Just wanted to add a note - BLD (the system that brakes the wheel without traction) cannot be turned off. So even with stability control off it's still active.
Hi Kevin, the manual for my '20 JLR generally supports your comment.

" A feature of the TCS, Brake Limited Differential (BLD), functions similar to a limited slip differential and controls the wheel spin across a driven axle. If one wheel on a driven axle is spinning faster than the other, the system will apply the brake of the spinning wheel. This will allow more engine torque to be applied to the wheel that is not spinning. BLD may remain enabled even if TCS and Electronic Stability Control (ESC) are in a reduced mode."

It does say "may remain enabled" though. I wonder if the manual is wishy washy on this point because the BLD is in fact disabled when the lockers are engaged?

Later,
Johnny
 

Wabujitsu

Well-Known Member
First Name
Jeff
Joined
Jul 26, 2019
Threads
104
Messages
2,259
Reaction score
4,432
Location
Sarasota, FL
Vehicle(s)
2021 JLUR, 2020 JLU Sahara
Build Thread
Link
Occupation
Retired US Army
Vehicle Showcase
1
Jeep Wrangler JL 2H vs 4H Screenshot_20201210-193617


James,

In the highlighted WARNING section, first bullet:
ESC "Full Off" mode is intended for off-highway or off-road only.

Also whenever I drop into 4Lo my 'ESC Off' indicator light comes on.

Jay
James, you are spot-on. I too have the ”ESC Off” indicator light up when I put my Jeep in 4Lo.

I found this, which I suspect refers to the JK, but ESC is identical in the JL. It clearly indicates that ESC turns off when the vehicle is put in 4Lo. http://www.jeeclub.com/reco-814.html
 

jeepoch

Well-Known Member
First Name
Jay
Joined
Nov 13, 2019
Threads
1
Messages
951
Reaction score
2,687
Location
Longmont, CO
Vehicle(s)
2019 JL Wrangler Sport S 3.6L Auto 2 door, 2.5" lift, 35s
Jeff,

Thank you. The linked article from Jeep Manuals (jeeclub.com) looks like it was indeed written around circa 2015 for the JK but as you said is still likely very relevant today for the JL.

I'm just highlighting the most interesting sections here for convenience (since it's not described well in either the 2019 or 2020 JL Owner's Manuals). Hopefully this helps clarify any confusion. Maybe not.

What is very informative is that ESC, TCS and BLD (as quoted directly from the JL Owners Manual) are all in play while in both 2Hi and 4Hi but are independently applied in 4Lo (with ESC being explicitly disabled)

From the JL Owner's Manual:

Electronic Stability Control (ESC):
"This system enhances directional control and stability of the vehicle under various driving conditions. ESC corrects for oversteering or understeering of the vehicle by applying the brake of the appropriate wheel(s) to assist in counteracting the oversteer or understeer condition. Engine power may also be reduced to help the vehicle maintain the desired path."

Traction Control System (TCS):
"This system monitors the amount of wheel spin of each of the driven wheels. If wheel spin is detected, the TCS may apply brake pressure to the spinning wheel(s) and/or reduce engine power to provide enhanced acceleration and stability."

Brake Limited Differential (BLD):
"Functions similar to a limited slip differential and controls the wheel spin across a driven axle. If one wheel on a driven axle is spinning faster than the other, the system will apply the brake of the spinning wheel. This will allow more engine torque to be applied to the wheel that is not spinning."

"BLD may remain enabled even if TCS and ESC are in a reduced mode."


Now directly from the Jeeclub article:

4L Range (4WD Models)

ESC Off


"This is the normal operating mode for ESC in 4L range.

Whenever the vehicle is started in 4L range, or the transfer case (if equipped) is shifted from 4H range or NEUTRAL to 4L range, the ESC system will be in this mode. In 4L range, ESC and TCS, except for the “limited slip” feature described in the TCS section, are turned off until the vehicle reaches a speed of 40 mph (64 km/h). At 40 mph (64 km/h), the normal ESC stability function returns but TCS remains off. When the vehicle speed drops below 35 mph (56 km/h), the ESC system shuts off.

The ESC is off at low vehicle speeds in 4L range so that it will not interfere with off-road driving, but the ESC function returns to provide the stability feature at speeds above 40 mph (64 km/h). The “ESC Activation/ Malfunction Indicator Light” will always be illuminated in 4L range when ESC is off."

In summary:
It looks like the braking systems on the JL (and likely all Jeep Models) are rather sophisticated. While the Electronic Stability Control (ESC) and the Traction Control Systems (TCS) can both be placed into 'Reduced' operating modes by the driver (via cockpit pushbutton), the Brake Limited Differential (BLD) always remains active.

Furthermore in 4Lo, ESC is explicitly disabled, TSC is potentially in a reduced mode and BLD remains enabled and active.

Wow. This is really good news. While in 4Lo my Sport has more capability than I had originally thought.

Please anyone correct me if I have any of this wrong.

Jay
 
Last edited:

TheRaven

Well-Known Member
First Name
Kevin
Joined
Oct 22, 2020
Threads
5
Messages
1,449
Reaction score
1,933
Location
Reading, Pennsylvania
Vehicle(s)
2021 JLU 80th
Occupation
Electrical, Mechanical, and Aerospace Engineering.
Wow. This is really good news. While in 4Lo my Sport has more capability than I had originally thought.

Please anyone correct me if I have any of this wrong.

Jay
Nope you're good. We enthusiasts make a much bigger deal out of things than we need to. All three diff types are going to be more than fine anywhere on road. The Rubicon has a little bit of an advantage in more technical off-road situations because of its lockers. But the Sahara is not going to be able to get any further than the Sport simply because of an LSD.
 

Sponsored

jeep-v

Well-Known Member
Joined
Aug 6, 2020
Threads
1
Messages
47
Reaction score
35
Location
PA
Vehicle(s)
2019 JLUR 2.0T
The funny thing was when I got a loaner 2021 Sahara and it was not even close to my Rubicon 2.0T during acceleration. At first, I assumed it is 3.6L engine, when in fact it was 2.0T. The reason
I felt less power is the axle ratio. And the fact is - my 2.0T Rubicon puts way too much torque on the rear wheels in 2H with all of the following consequences. Possibly, the reason 3.6L is not experiencing it - it has less torque. I could make rear wheels spin in dry condition without even pushing accelerator all the way to the floor. Unless I have some crazy tuned Wrangler, which is possible as I am not the first owner. But there is no any mods that I could see on it and it appears to be stock. All I know the first owner has some affiliation with sheriff office in NC and retired Vet based on stickers attached to rear window.
 
Last edited:

alksion

Well-Known Member
First Name
Josiah
Joined
Jan 3, 2021
Threads
74
Messages
2,415
Reaction score
3,414
Location
Brea, CA
Vehicle(s)
21 Rubicon 392, 21 Sahara Altitude
Occupation
Biz Owner
Wow read through every page. I think I could have got unstuck yesterday in about 16 inches of snow if I would have went to 4L. Only issue was that I was stuck and could not be rolling slowly to engage 4L.
 

alksion

Well-Known Member
First Name
Josiah
Joined
Jan 3, 2021
Threads
74
Messages
2,415
Reaction score
3,414
Location
Brea, CA
Vehicle(s)
21 Rubicon 392, 21 Sahara Altitude
Occupation
Biz Owner
I was trying to push the button for ESC in 4H to no avail.
 

Sponsored

auxSwitch

Well-Known Member
First Name
Tim
Joined
Jan 2, 2018
Threads
2
Messages
693
Reaction score
4,926
Location
The Nutmeg State
Vehicle(s)
JT Rubi, FZ6
Vehicle Showcase
1
Lay,

[Edited from peer review feedback.]

One thing not really well understood about 4wd is that it depends on the type of axle, or rather the locking differentials, and whether (or not) you have them. Rubicon's have full lockers on both axles. Most (or probably the majority) of Sahara's have a Limited Slip Differential (LSD) on the rear, which isn't a true full locker. But in some ways it's even better. However like the Sport, the Sahara has an open differential (non-locking) in the front. Finally, most Sports come from the factory with only open diffs on both front and rear axles. Of course there are always some variations, but that's the general rule of thumb when thinking about the various Jeep trims.

Regardless of the trim level however, all axle types are pretty much always open diffs when 'unlocked'. The LSD is the only exception. It's potentially always partially 'locked' or possibly slipping all the time. For the locking diffs, they can only be locked in 4Lo (unless you have special overrides to very specific software calibrations via various third party programmers).

When 'unlocked' or with open diffs one and only one wheel on a particular axle, is getting power (when traction is lost). In fact the power is generally reduced to both wheels during 'slip' such that the overall contribution to motive effort from that particular axle is marginal.

So for every Jeep trim in 2Hi only one wheel (not two) is essentially getting power at the instant when either wheel starts slipping. Either can be powered but only the wheel with the least resistance is the one getting the most energy from the powertrain.

Noting that an open diff axle will distribute power to each wheel equally (50%) but ONLY with adequate traction. Once any wheel starts slipping, power is reduced to both wheels with the slipping wheel getting the most torque. Certainly not advantageous. That is exactly why lockers are so much better.

Also for every trim package when in 4Hi, potentially only two wheels are powered. One wheel in the front and one wheel in the back (if both axles are slipping). Again either wheel on each axle will be powered but only one per axle. So both 2Hi and 4Hi are misconceptions and named improperly. They should be named 1Hi or 2Hi respectively (while slipping). But since either wheel can be powered at any instant it's still considered 2 or 4wd respectively.

Only when in 4Lo do more 'powered' wheels potentially come into play. Only (ONLY) the Rubi's with the full lockers can have all 4 wheels powered (all the time) independent of any slipping wheels. When 'locked' all 4 wheels spin at exactly the same rate and the available torque is equally divided to all four wheels. This makes the Rubicon the only truly possible 4 wheel drive Jeep.

The Sahara with the LSD in the rear and an open diff up front when in 4Lo will have at least 3 powered wheels (during slip). The power to either rear wheels will be variable depending on the clutching action of it's LSD diff. So both rear wheels will have some fraction of the total available torque. However, they will both still be powered. In many situations, the LSD is far superior to the full locker because it will better adapt to give the most power to the non-slipping wheel. However, the Sahara's front axle is exactly like the Sport with an open diff.

With the Sport due to the open diffs both front and back, when in 4Lo it can have a potential of just two powered wheels, one on each axle if they're each slipping. So for the Sport it really can only ever achieve at best 3 but sometimes just 2wd, depending on which wheels on which axle are slipping. Again because either wheel on both axles can potentially be powered it's still considered 4wd.

So in summary (during wheel slip):
Sport:
2Hi -> 1 powered wheel (rear)
4Hi/Lo -> 2 powered wheels, 1 front 1 rear

Noting that most typically only one axle is experiencing slip so effectively there are 3 powered wheels.


Sahara with the LSD:
2Hi -> 2 variably powered wheels (rear)
4Hi/Lo -> 3 powered wheels, 1 front 2 rear

Note that with the LSD, it will always have at least 3 powered wheels during slip.


Rubicon:
2Hi -> 1 powered wheel rear
4Hi -> 2 or 3 powered wheels, same as the Sport

4Lo:
unlocked -> 2 or 3 powered wheels, same as the Sport
locked -> 4 powered wheels, 2 front 2 rear all the time

So advantage Rubicon. It is the only Jeep trim that can have all 4 wheels powered all the time independent of any slip.

I drive a lifted 2019 Sport with 35s. There are fortunately ways to compete with the Rubi's. I've done many trails successfully where some Rubicon's (almost all stock) had to be assisted. The secret is TRACTION. I've added a Sway Bar Quick Disconnect kit for added articulation and I've got a particularly light foot to keep from spinning any wheel. I also invested in really great 35" A/T tires. Regardless of your Jeep, independent of your 4wd selection mode TRACTION is always your best friend!

Hope this helps.
Jay
I'm sorry... how does this post have only 1 like? and how is it not on required reading to join the forum? I am sure this is all internalized knowledge for a bunch of jeep sages out there, but for those of us who are new(-ish) to jeeps - this is gold. Even Jeep videos weren't as clear.
 

aldo98229

Well-Known Member
First Name
Aldo
Joined
Nov 16, 2019
Threads
86
Messages
11,019
Reaction score
27,682
Location
Bellingham, WA
Vehicle(s)
2023 Jeep Gladiator, 2018 Fiat 124 Spider
Occupation
Market Research
Vehicle Showcase
3
I'm sorry... how does this post have only 1 like? and how is it not on required reading to join the forum? I am sure this is all internalized knowledge for a bunch of jeep sages out there, but for those of us who are new(-ish) to jeeps - this is gold. Even Jeep videos weren't as clear.
Perhaps because not everyone agrees with it...?
 

Bo Ran

Well-Known Member
First Name
Randy
Joined
Jan 28, 2022
Threads
8
Messages
45
Reaction score
33
Location
76034
Vehicle(s)
2021 Rubicon 392
I'm sorry... how does this post have only 1 like? and how is it not on required reading to join the forum? I am sure this is all internalized knowledge for a bunch of jeep sages out there, but for those of us who are new(-ish) to jeeps - this is gold. Even Jeep videos weren't as clear.
The information you presented is EXCELLENT--Thank you! Please forgive my question. I should probably know the answer but I am confused about when to use 2H in a Rubicon 392.
I literally just picked it up at dealership yesterday. The salesman told me to leave it in 4H auto for normal highway driving.
Other less robust (also now recognize wrongly named) 4WD vehicles I've owned were normally driven on paved roads or highways in 2WD. If inclement weather or slippery conditions existed I'd always shift into 4WD.
My assumption is that less horrible gas mileage might be achieved in 2H?
What is your advice as to normal roads, dry conditions? 2H or 4H in Rubicon 392?

Thanks for your great comment!
 

Heimkehr

Well-Known Member
First Name
James
Joined
Sep 3, 2020
Threads
31
Messages
7,029
Reaction score
13,950
Location
Pennsylvania
Vehicle(s)
2021 JLU 2.0T

Bo Ran

Well-Known Member
First Name
Randy
Joined
Jan 28, 2022
Threads
8
Messages
45
Reaction score
33
Location
76034
Vehicle(s)
2021 Rubicon 392
The 392's full-time four-wheel-drive system doesn't offer a two-wheel-drive mode.
Sorry--for sure! Studying the Wrangler Owner's Manual. Just found the separate book for 392. They gave me almost 500 pages of information. Trying to sort out how to not break stuff. :)
Sponsored

 
 



Top