Limited- 4WD- Dumb Question

Being that the limited is AWD is it still good to exercise the system by putting it in H4L or L4L every once in awhile? Or is that not a concern because its always in the H4F?

 

You’re still exercising the actuator by periodically engaging H4L and L4L.

 

Yes. As stated above you’re exercising the actuator

 

Good practice, yes.

 

Full time 4WD ≠ AWD.

 

You should still engage 4H/4L periodically, yes.

It’s important that all of the actuators get cycled to prevent freezing up and leading to expensive repairs. My wife’s Sequoia went from a fully capable 4wd to 2wd only because she would never exercise the actuators.

 

Can you explain the workings of the Sienna’s drive train please? I thought the AWD system was controlled by the computer, so driver input to exercise it wouldn’t be required. Asking out of ignorance with no snark intended.

 

I know nothing about the Sienna. I have a 12’ Sequoia and the 4wd system is similar to the T4R Limited.

 

There’s so many variations and exceptions out there in systems that AWD, 4WD is largely marketing. (and always has been)

There is a few generally agreed upon definitions but there’s enough variation for me to not want to correct folks.

In lighter-duty mechanical systems like the RAV4, it’s just a simple computer-controlled clutch that sends power to the rear and its used often as opposed to the much larger mechanical components/linkages that move to shift into 4WD in our beefier transfer cases. (and can seize up if left in position for years - “AWD” in the Sequoia might still let you shift into 2WD and those components are similarly beefy)

For lighter-duty Toyota hybrids such as the Sienna and Prius, AWD is added on by an electric motor being added to the rear axle, similarly idiot-proof.

 

Not an electric motor, at least on Toyotas I think.

 

That's more similar to the SR5, OR, and Pro, with a dedicated 2wd mode. 4R Limited use I think H4F for the daily full time 4wd driving mode, H4L for center diff locked, and L4L for center diff locked plus low range.

 

Yes, I believe you are correct. Main difference is that my Sequoia has a center differential lock, so it’s a bit different than the SR5, OR.

 

Toyota calls this system Full Time 4wd as opposed to AWD. AWD's dont have a locking center diff or a low range.

 

The practical difference between Full Time 4WD and AWD is that the former is proactive and controlled by the driver, and the latter is reactive and controlled by the computer. Driving modes not withstanding.

 

Yeah - probably more importantnto activate the center looking diff regularly.

 

It is interesting to note that the owners manual for my 2022 only mentions periodically exercising the 4WD system in the Part Time 4WD section and not in the Full Time 4WD section. However, I agree with others it seems prudent to exercise all modes of the Full Time periodically just as recommended for Part Time.

 

I believe that Toyotas intent with the suggestion that PT 4WD be engaged periodically is to ensure that the front drive components remain lubricated - which is not needed with FT 4WD as these components are always turning. However, I agree that it is wise to lock the center diff on FT 4WD's, and put the gear box in low range, occasionally to exercise the actuators. On my daily drive to work there is a stretch of road that is dead straight for about 1-1.5 miles. Once a month, I lock the center diff on my FT 4WD 4Runner and drive that stretch of roan in H4L. Once I get to work, I go into L4L and drive in a straight line for a short distance in the back of our parking lot a few times before parking. Did the exact same thing with the 2010 PT 4WD Tacoma that I drove for 13 years before I got my 4Runner. Never had a problem in those 13 years with the Tacoma going in/out of 4HI or 4LO - ever. So far, no problem with the 4Runner ever going in/out of H4L or L4L.

 

The common failure point of the part time 4wd system is the ADD actuator on the front differential. This is the actuator that tends to stick if not used. As full time 4wd dont have this part, you really dont have to worry about it on the limited models. However, cant hurt to actuate the center diff components occasionally...but you need not be as concerned as the part time 4wd owners.

 

Yep, I'm not a Torsen differential expert, and it has been a while since I looked at one in detail, but basically a Torsen center differential is a second, smaller planetary gear set in the transfer case, in addition to the larger planetary gear set that provides low range gearing. The smaller Torsen planetary gear set allows the front and rear output shaft to turn at different speeds (so no drivetrain binding when making turns on high friction surfaces) and allows different power output between the front and rear output shafts based on differences in traction between the front and rear tires (on a late model 4Runner Limited this would be H4F). The center differential outer housing has gear teeth on it. A shift sleeve can slide over and lock onto this gearing on the center differential outer housing - which, in effect, bypasses the center differential planetary gearing and locks the center diff such that the front and rear output shafts turn at the same speed (on a late model 4Runner Limited this would be H4L = 4HI on a PT 4WD 4Runner). The shift sleeve is moved by a shift fork attached to an electronic actuator. On a FT 4WD vehicle with a center diff you are exercising these actuators and shift forks to ensure they don't seize up by occasionally going into H4L and L4L - even when you don't need it. On a PT 4WD drive vehicle you are also exercising similar actuators - but more importantly, you are lubricating components in the front wheel drive system that are not normally moving when you are in 2WD.