Toyota 4WD systems explained

brillmtb · May 2002

I believe that there are different types of Limited slip differentials and I would be very suprised if you could demonstrate a difference in tire wear on normal driving around corners.

brillmtb · May 2002

I think most of what you have said is correct. I found a review of the Sequoia (the new system for the sakes of this site) where, for the first time, the reviewers did not like the system in serious off roading. One guy went as far to say that he wished he had wire cutters by the end of the test to disable the electronic control of the system.

While I think this is an extreme statement and the system probably works well in standard snow/ice settings where it did not preform well in the review was in sand.

It seems that when all wheels had limited traction and the driver was tring to carry momentum through a loose sand section to avoid getting stuck (anyone who had done 4wding knows this situation well) the Toyota system in the Sequoia first started breaking the wheels then powering down. This apparently resulted in decreased momentum and getting stuck.

It seems like this could be a potential reality and not some made up story by a die hard chevy guy but I would love to test it out if I can find a friend with a Sequoia.

I think the more control you have over a system the better. I have the Montero and it has settings for 2wd, 4wdhi, 4wdhi-lock, 4wdlow with a limited slip rear. You just have such good control. I personally have seen the difference between the AWD-like setting (4wd hi) and 4wd hi lock with the lock setting giving me better positive control over the vehicle in mud where I would have ended up in the river if there was any hesitation in the system at all. So I know first hand what you mean when you say that putting power to all 4 wheels with a 50-50 fixed slit is often times better than letting the vehicle chose.

Also, dosent the Subaru, and most all AWD, limit the power available to the front wheels. Some are only up to 30% I think.

pschreck · May 2002

I'd like to read that review, where can I find it? It's unlikely that I'll ever be in the sand as I hate the sand and beach in general.

I agree with your statement about having control over your system. Just one reason that I wouldn't want a truck that only offers AWD. Of course if I were to do any SERIOUS offroading I'd want something smaller than a F/S SUV anyhow.

As to the Montero, it is just too small to suit our needs at this point in time. Then there's that rollover thing.

cliffy1 · May 2002

It took me some time, but I went back through the archives of the Sequoia topic to find a post from a Sequoia owner who used it off road. Below is a cut and paste of a post from Slickrock who seems to have abandoned the Town Hall.

While looking for this, I was reminded of how long Heatwave has been looking for things to complain about.

#1760 of 5543 Sequoia in Sand and Sandstone by slickrock Mar 29, 2001 (09:59 am)
Thanks Cliffy, I thought nobody would ask...

I spent a fair amount time off-road last week in Moab, Utah, and learned quite a bit about how the Sequoia performs in actual off-road conditions. The trails were rated up to 3 1/2 (at 4 you risk vehicle damage), and included sand, slickrock (sandstone), streams, and slopes. I have some pictures, but haven't figured out exactly how to share them here.

First let me say that my baseline is an older ('84) stick-shift Landcruiser, so while the Sequoia was different, it was familiar in many ways. Here are some observations and possible points for later discussion.

The Sequoia can do trails rated up to 2 1/2 in high range. Beyond that you need low range. I will limit the rest of the discussion here to low range performance.

In low range, the Sequoia has plenty of engine and braking power for the steepest hills (~35 degrees) that I tried. It also had no power problems climbing ledges, but traction was sometimes an issue when there was loose dirt mixes in with the rock.

I did some experimentation in Low/Low (locked center differential) vs Low/Second (VCS/Tracs). What I found was that you had to turn VCS off, otherwise it kicked in (and messed with the throttle and braking) when you didn't want it to, because the wheels will slip on sand and dirt.

On the other hand, I ran into at least one case climbing a dirty rock ledge where L/L wouldn't make it up(diagonally opposite wheels were slipping), but L/S (and Active-Trac) got me up. It was not smooth or quiet, but it outperformed the locked center differential.

However L/S was deadly going down hill (on steep hills). There was definitely insufficient engine braking. But you don't need (or want) Active-Trac going down hill. So my rules for off-road driving-mode selection are actually pretty simple:

1. In 4WD Low Range off-road, turn off VCS (push the button) and use L/D.
2. In Low Range going up a difficult hill, use L/S (Active-Trac).
3. In Low Range going down a difficult hill, use L/L (Max. Engine Braking).

The second thing I noticed is that size matters. The Sequoia is long and wide. The width came into play in maneuvering around large (>1 ft.) rocks on the sides of the trails and narrow trails. There were also some very tight turns that required a bit of jockying. But it's better than a Hummer, and to tell the truth, the tightest turns were in the City Market parking lot.

The length is another story. The Sequoia is a looooong truck. It has plenty of ground clearance (I may have hit the skidplates once or twice), and so the breakover angle was not a big issue. I thought the running boards would take hits, but they are high enough and tucked in well enough that they were not a problem. But I would want to remove them (8 bolts each) before trying a 4-rated trail.

I only touched the underside of the front bumper once, so I am satisfied with the approach angle. But the departure angle (and that long tail) leaves a lot to be desired. I hit the trailer hitch receiver many times (that's to be expected -- I consider it part of the skid plate system). But I also hit the underside of the giant one-piece plastic rear bumper a few times (which is 2" higher, but who said the rock was perfectly level).

The PLASTIC bumper is definitely not part of the skid plate system (or at least not for very long). Hey Toyota people who supposedly read this board, when sandstone meets plastic, guess what always wins!! This was a design mistake.

So crossing gullys (and any other concave surface) became an interesting challenge, and I would have to say that the limiting factor to the Sequoia's off-road performance is the integrity of the giant one-piece rear plastic bumper cover.

Do 2001 4-Runners and Land Cruisers also have these plastic bumber covers??

I should also mention tires. I did these trails with some trepidation given the stock passenger car Bridgestones. In the future, I will replace them with something starting with LT and having a C or D load rating. Maybe Michelin LTX A/T 265/75R16's. That would be add 1/2" to the height, and be much safer off-road. The odometer would take a 3.4% hit (that improves the warranty), but the speedometer would finally be right. I also think the ABS/VCS/Tracs ECU's could wouldn't notice the minor difference.

Beyond the 1/2" tire lift, I do need a solution to protecting the left and right underside of the rear bumper cover. Some sort of real skid plate or sacrificial add-on. Any suggestions would be welcome. I would be reluctant to consider lifts or air shocks, because I don't want to mess too much with the suspension or ride. Maybe TRD or Toyota off-road will offer something someday. In time there will be Sequoias in the junkyard with good rear bumper covers. Maybe I can make something suitable out of one of them.

Finally, I must say that it was a pure pleasure to cruise the western freeways at 75-80 mph. I never felt fatigued even after a full day of driving, and the vehicle generally performed flawlesly on the highway. On the other hand, it only got 15 - 16 mpg at 75 mph (I suppose it would have done better at 55 mph).

wwest · May 2002

May I suggest new definitions for SUV categories ???

Some people need/want SUVs for SPORTS off-road.

Others simply want an SUV for reliable "on-road" wintertime, or any low traction surface, point A to point B, travel.

It occurred to me on reading the above posts that maybe what is needed is a third SUV category that the manufacturers and the public can use to define their vehicle's capabilities.

Categories.

1. SUVs like the RX300, Highlander, and MDX that are primarily minivans with four doors, high seating and reasonably large interior volumes but little or no ability to travel in wintertime relaibly on low traction surfaces.

2. SUVs such as the Sequoia, X5, and ML that can travel on wintertime low traction surfaces reliably but cannot and/or should NOT be used for true SPORTING style off-road.

3. SUVs that fall into the Jeep category, can be used in true off-road SPORTING events, mud racing, etc.

cliffy1 · May 2002

How about Sport wagon, Sport utility vehicles and utility vehicles? I actually disagree with your assessment on the Sequoia, but I get your point.

pschreck · May 2002

Does your Porsche have any LSDs in it, or does it get around them by using the AWD and a great set of tires for traction purposes? Just wondering.

wwest · May 2002

My 2001 911/996 has PSM and a VC mounted in the front in line with the drive line to the front diff'l. The PSM system supplants the need for a mechanical LSD by applying moderate braking to either rear wheel that loses roadbed traction.

I suspect, but don't really know, that there is no PSM/LSD activity at the front wheels since the clear majority of torque is always to the rear wheels.

I have never had the PSM actuate the traction control mode yet (both rear wheels slipping) but I understand it to be much like the GS300, apply braking first and then moderate the throttle if the driver doesn't.

cliffy1 · May 2002

So, according to what Wwest tells us, it looks like Porsche did things on the cheap like Toyota by eliminating the LSD (aka magic differential) on its model.

jynewf · May 2002

The Land Rover Discovery and Range Rover also use a braking-type system. In the case of the 99-2001 Discovery, the braking/traction control system is the only torque distributing system. There is no center locking, VC or LS diff, either in HI or LO mode, in the 99-2001 Disco.

Also, the Mercedes M-Class also uses such a system, and Audi may have also used a braking type system in some of its cars in the past, along with a torsen center diff.

Notwithstanding Heatwave3's earlier comments, Toyota certainly is not going it alone in implementing such a system in its vehicles.

pschreck · May 2002

I was just going over the posts from the past couple of weeks. There seems to be a few missing. I wonder why.

pschreck · May 2002

I think you are correct in your prediction as to the demise of the old systems. Technology doesn't stand still does it?

Thank you for answering my question about your Porsche. I can only imagine what it must be like to climb into something like that, let alone drive it.

wwest · May 2002

Yes, and disc brake pads can be replaced in very short order by even a simple-minded DIY'r. Not like LSD clutch paks at all.

wwest · May 2002

Software instead of LSD hardware....on the CHEAP?

Cliffy1, you obviously haven't hired a really good "real time" programmer lately !!

pschreck · May 2002

I believe cliffy was being sarcastic toward an earlier post.

You certainly are correct about brake pad replacement vs LSD replacement.

pschreck · May 2002

Land Rover doesn't use LSDs or VCs in their trucks? Holy cow! How do they get out of their driveways? ;-)

Love my Sequoia!

brillmtb · May 2002

I will check my stack of mags for you to see if I still have it. I did some spring cleaning and hope it did not get tossed. I think the post after yours placed by the Sequoia owner also suggests some difficulty with the system under certain conditions like sand. I think Toyota will get the bugs out of the system and predict they will add in features that give the driver more control over the power distribution but we will see.

Size: To tell you the truth I didnt think the Sequoia was so much bigger than the Montero that it would have made a difference to me. I end up pulling a trailer and may add a trunk on top but both situations would dictate that I jump to a full sized pickup with a crew cab to match or exceed those capacities. As such I am waiting for the new Ford diesel 6cyl with 400 ft lbs of torque next year. If they add a new truck, which is the rumor, that has a crew cab and 6ft bed this will handle both people and cargo better than an SUV. I am keeping the Monte because it does everything so well for its design. Forget about the roll over thing. I have talked to so many people who really use these SUV in high risk situations and roll overs is a concern for every SUV, not just the Montero. Also, the folks in Australia tell me they have had no reported problems and they even disconnect the sway bars for increased articulation.

pschreck · May 2002

Are you talking about the Tonka Ford with the hydraulic (sp) assist? That sure does look interesting.

pemarsh · May 2002

If the trans is in "drive", and I hit the 4wd button...is the power to the front and back each 50% ??? Is the power to each tire 25%??

cliffy1 · May 2002

In response to your message yesterday, Pschreck was correct in that I was being sarcastic. I appreciate your response to his question.

cliffy1 · May 2002

The answer is a qualified "yes". It is qualified because it is only 25% per tire if traction conditions are equal at each tire and you are not turning a corner.

wwest · May 2002

My friends often use me as the "straight" man in their jokes because I'm so slow to pick up on the fact that I'm being "ribbed".

brillmtb · May 2002

I dont know the meaning of "tonka" but it is my understanding that they did go to hydraulically actuated valves, dropping some 140 parts and from what I was told it should be almost as quite as a gas motor.

If true, Ford is going to hit a home run with this and the V8 6.0l 600 ft lb torque diesel motor. There are plans to put it in the Expedition as well.

brillmtb · May 2002

It seems that my comment about updating the "Sequoia-like" VSC/Trac systems has already happened with the new Range Rover per the Speed Channel last night.

Seems that the Range Rover folks noticed that there is a problem with this kind of system in certain situations where you need to maintain momentum, such as sand or mud, but where there is a risk of the motor powering down in an attempt to limit wheel spin.

What they have done was to place a switch in the Range Rover to disable the VSC/Trac in these situations. This reverts the system back to something more like a standard 4wd lo/high range that will deliver power to the most number of tires all the time, slipping or not.

This is what I think Toyota will realize in thier next generation systems. Until then, I think I still prefer driver controlled systems but I understand that not everyone is able to drive well on snow and the Toyota system should keep them out of trouble most of the time.

wwest · May 2002

Nice thing about using software and "flash" non-volatile memory to implement functions, retrofitting new functionality is a piece of cake.

pschreck · May 2002

I referenced Tonka from Popular Science or Popular Mechanics. I'll see if I can find the magazine I saw it in.

The Sequoia does have a VSC shutoff switch however I doubt that I'll be seeing mud deep enough to have to worry about it.

I'm not sure how a part time 4WD system is any more controllable than a full time 4WD system.

stever · May 2002

Ford Mighty F-350 Tonka

Didn't you play with "Tonka Toys" when you were a kid, Brillmtb?

Steve
Host
SUVs, Vans and Aftermarket & Accessories Message Boards

wwest · May 2002

Controlable, I think, is not the issue.

A part-time AWD/4WD system is called Part-time because it should NEVER be engaged on high traction surfaces. Part-time mode typically engages a SOLID connection between the front axle and the rear axle so they MUST rotate at exactly the same rate. When turning, front axles will inherently rotate at a rate different from the rear, but this is not a problem on low traction surfaces wherein the tire/roadbed "interface" is marginal and the slippage necessary to relieve the strain on the drivetrain can be accomplished there.

Controlability only really comes into play if you have a Part-time system improperly engaged. In a tight, accelerating turn, for instance you might break your fingers, knuckles, or even parts of the drivetrain itsself.

A full-time AWD/4WD system is one wherein the front axle and the rear axle remain coupled at all times but in not so solid a manner that some independent rotational rate cannot be accomodated.

brillmtb · May 2002

I also thought that AWD/Full Time would work better than part time mode until I actually started 4 wheeling in more hair raising circumstances. There is a difference. Its hard to explain but was very easy to see on my last visit to the fishing hole in the mud. I have imediate control of the front end, I mean within inches, in the part time mode. I think I may have gone swimming in the river if I had not. If you out in Oregon sometime I'll take you out and show you the difference.

I dont think you would notice it on the street (ie snow) as much.

When you turn off the VSC, what does the Sequoia now NOT do that it could before?

brillmtb · May 2002

I dont think I will need that Tonka truck anytime soon. I dont think I could find something large enough to tow with the 600 ft lb motor either.

I am very interested in the v6 400 ft lb diesel that Ford is coming out with. There is a rumor that a slightly larger truck than the F150 will come out to accomodate a 6ft bed and crew cab. That would be perfect for me. Towing ability that surpases even most of the V8 gas motors with the mileage of a diesel. Way cool

cliffy1 · May 2002

Turning off the VSC stops only the lateral skid sensors from kicking in. This is something you wouldn't want to do on the street, but would have some advantages in mud and sand.

wwest · May 2002

brillmtb;

Now you tell me...

I just returned from Nyssa in my 01 AWD 911 but I don't think I would have been taking it to any fishing holes anyway.

I also have an 01 AWD RX300 in which I am quite throughly dissapointed with regards AWD capability. Previously I had an 85 and a 92 Jeep and both had full-time and part-time modes. Made many trips to bachelor with chains on all four wheels in part time mode.

Full time is good for "normal" use but when the going gets tough the tough get going in part-time mode.

pschreck · May 2002

I'm not saying that I believe that full time is better than part time while four wheeling out in the woods. I don't know. I've never taken the Sequoia four wheeling like I used to go back in the day. When you said "control" I thought you meant control how the drive system functions. As in on,off, high, low, locked, unlocked.

I DO believe that as an ALL AROUND system, ActiveTRAC is the ticket. I found that with part time 4WD, it was only useful in the snow or while off roading.

If I wanted to really go four wheeling, I'd probably want an old Land Cruiser or maybe a old Land Rover. I simply can't justify trashing out a 40,000 dollar vehicle just to go woods running.

What I was saying is that I don't understand how full time 4WD is any easier to use than part time 4WD. In fact, from the example that you discribed above, I would think it would be more difficult to get the results that you are seeking.

As far as the VSC, I think cliffy would be the better person to answer that question. You see, I just don't have the stomach to take any real chances with my truck yet. My guess is that you could allow the front end to plow or the rear end to swing around easier.

pemarsh · May 2002

I understand now that the Sequoia with 4WD "hi" has equal power to all the wheels, and this can change depending on road conditions.

My question is that if I drive the Sequoia in bad road conditions (slushy/snowy/muddy, etc.) over 25 MPH, what is the Sequoia going to do while I am in 4WD??

pschreck · May 2002

My experience is that it will just go. Quite nicely in fact. No noise, no nonsense.

cliffy1 · June 2002

It will work just fine in 4WD in the road conditions you describe. Power will be distributed roughly 25% per tire unless one tire begins to turn faster than the others at which point the ABS will pump the brake at that wheel to keep more power to the other three wheels.

wwest · June 2002

The way I ran the Jeeps was:

In the summertime in 2WD mode, mostly for the additional economy and to reduce wear on the front portions of the drivetrain.

In the wintertime in full-time AWD/4WD, torque delivered primarily to the rear and adjusted via a VC if things got slippery.

Really serious road conditions, or with the need for snowchains, I put it in part-time mode. It was never left in this mode for any extended period. Part-time mode got me up and going on many occassions when the full-time mode just couldn't hack it.

I never had it in low range and it never went off-road except to get around freeway stalled car blockages.

cliffy1 · June 2002

Here is an experience that was told to me by a customer of mine. This is actually the same guy that test drove with me on the icy parking lot. He owns a Land Cruiser with the A-Trac system and called me with a concern. It seems he ran off the road on two different occasions. This was on an icy road with deep snow on the sides. From his account, it seems he entered the corner at a fairly high rate of speed. The VSC did not help him maintain control. When I asked him about this, I discovered that he was applying the brakes in the corner. This effectively disables the VSC (lateral skid control). By applying the brakes, you override this part of the system.

He kind of laughed when he realized what was happening. He will be modifying his driving technique in the future.

The next part of the conversation was also instructive. I asked him if he was able to get out of the ditch. "Oh yeah. Getting out was no problem. The snow was fairly deep but I didn't even bother to lock the center or put in in low and I pulled right out. I was just worried about why I was there in the first place."

This is one of the few Land Cruiser customers I have ever sold to that is actually using the vehicle in the manner it was intended. He takes it off road a good bit, including a trip to Alaska. He couldn't be happier with the A-Trac system, especially now that he knows how to better employ the VSC portion of it.

wmquan · June 2002

"... I discovered that he was applying the brakes in the corner. This effectively disables the VSC (lateral skid control). By applying the brakes, you override this part of the system."

This is _exactly_ why the electronic stability control system in Toyotas (VSC) is not as good as the Mercedes-Benz ESP, BMW DSC, and Audi ESP systems. Toyota's VSC (and Acura's VSA) are not full-range stability control systems. With VSC, if you apply the brakes, you lose skid control capability.

Whereas MB ESP, BMW DSC, and Audi ESP systems are full-range, so that even if you're applying the brakes, the sensors are still looking for potential skids, and will selectively brake individual wheels even harder to attempt to stop the skid.

I don't know if Subaru's stability control system is full-range, but if anyone knows, I'd really like to hear from them.

Now, I think having VSC in Toyotas is a good thing. But it's only half of a good stability control system.

This is something that is lost in the marketing quest to say you have a stability control system. NHTSA cites the benefits of those systems, but they don't mention the difference between a full-range system and one that is not full-range. Stability control systems are not created equal.

wwest · June 2002

Can't overcome the laws of physics, so says Porsche.

If he was on the brakes and still slid into the snow then it is unlikely that VSC, PSM, and whoever's system would have helped him out.

I still think any VSC system should have a "stick-shaker" equivalent to let the driver know what he is doing wrong.

pschreck · June 2002

You may be correct, I don't know. What I do know is that the Sequoia is a lot less expensive that any of the vehicles you mentioned. And I don't believe any of those manufacturers even make a F/S SUV, so their system would do little good for people who need such a vehicle.

wmquan · June 2002

Yep, you can't overcome the laws of physics, and drastic situations. But there are plenty of cases where you have _some_ traction, hit the brakes to slow down, and the vehicle begins to skid / fishtail. That's when the full-range stability control system becomes important. Folks who drive ML's, X5's, etc. have experienced the ESP/DSC correction while coming off of slick ramps, etc. so it definitely works.

I know that those manufacturers don't make a full-sized SUV, but it doesn't mean that Toyota should have left VSC as a non-full-range system.

cliffy1 · June 2002

Could you possibly post a link for the information you have posted? I find it hard to believe that any system can actually function when you are already hard into the brakes in a corner.

wwest · June 2002

A completely "FULL" range "VSC" (stability) system would automatically RELEASE the brakes on the wheels wherein braking is NOT needed for corrective yawing motion and I doubt if you mean that.

On a slippery surface such as described it seems to me that the first action automatically asserted would be ABS. Almost all newer systems have ABS with automatic brake pressure distrbution also. When ABS is on, it is there to help the driver maintain directional control, oftentimes to the detriment of "braking".

If ABS was "on", as it certainly should been (remember he "slid" into the snowbank, obviously out of {directional} control) how is the full-range stability control to work?

It can't "tighten" the braking on the correct wheel to correct the yaw, the ABS is already preventing that wheel from "stalling". The only choice is to release some of the braking effects on the opposite wheel(s) and I rather doubt that ANY manufacturer will be going THERE any time soon.

Next you will say he shouldn't have been on the brakes anyway, he should have let the system save his butt.

cliffy1 · June 2002

Bingo! The driver was left with a choice that he didn't know he had. The choice is to slow down by applying the brakes (usually a bad idea in a corner anyway) or allow the VSC to assist him through the corner. He choose the former and found that the A-Trac system works quite well from a snow filled ditch.

I guess the lesson in this is that while you have a great system, it doesn't give you license to drive too fast for the road conditions.

wwest · June 2002

I'm still looking forward to the day that the ABS is redesigned so it doesn't activate as long as the vehicle is under directional control. Or maybe use an accelerometer to determine at what braking level can be achieved without ABS interference, or minimum ABS intervention.

The highest level of braking is oftentimes achieved with all four locked up, and under those conditions if it is my desire to stop straight and short then ABS should stay the hell out of my way.

wmquan · June 2002

"It can't 'tighten' the braking on the correct wheel to correct the yaw, the ABS is already preventing that wheel from 'stalling'. The only choice is to release some of the braking effects on the opposite wheel(s) and I rather doubt that ANY manufacturer will be going THERE any time soon."

Actually, that is exactly how full-range stability control works in such a situation! At least on MB's ESP. It can redistribute braking effort (when needed, based on inputs from the steering angle sensors, yaw sensors, etc.). The redistributed braking effort can be done across different wheels to at least try to redirect the vehicle into the intended line, breaking (braking, heh) the skid.

One big advantage to the true, full-range stability control systems is that the less-experienced driver doesn't need to do something that is non-intuitive -- e.g. apply throttle to add more speed to an already precarious situation. They can hit the brakes, and ESP will do its best, limited of course by the ultimate amount of traction and the laws of physics. Nothing will help you if you go beyond those, of course.

Here's some info from an ML enthusiast's page. Sure it's an enthusiasts page but this is a good English explanation of this scenario:

"... what happens during full force braking inside the ABS regime when no additional force can be applied without saturation? ESP will then invert, and momentarily reduce the brake force on the other three wheels, just enough to produce a realigning momentum."

http://www.whnet.com/4x4/abs.html#ESP

toygirl · June 2002

OK you Toyota PROS, I have a 4WD 2002 4Runner in Tejas, it rains for two days, still raining with lots of standing H2O and I need to go on the hwy. Am I ok to use my 4WD? I get differing opinions on this... to clarify, 4H, not touching the diffy button.
thanks!

pschreck · June 2002

It is my understanding that the 4Runner uses the same ActiveTRAC system as the Sequoia. If that is the case, you can drive the truck in 4WD all you want. My Sequoia is rarely out of 4WD. I only take it out of 4WD when I'm on a dry highway. In fact my brother and I drove from the GA/FL line to south central PA in 4WD in the rain while averaging 75mph.

Don't bother talking to the Ford, Chevy or Dodge guys with Part Time 4WD systems. Those manufacturers don't make a Full Time 4WD system.

Read messages #1-3 on this board. Just click on the "beginning of discussion" link at the top of this page.

pschreck · June 2002

Message #3 confirms that you will be fine running in 4WD anytime you want too. You'll love it in the rain. It's one of the real pluses of having Full Time 4WD.

Toyota 4WD systems explained

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