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Toyota 4WD systems explained

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  • I am looking for a simple explanation describing the applicable conditions (when to use each and why) for using the (1) Auto LSD System; and (2) (when and why) to disable VCS or A-Track. This will sound dumb, but the Owner's Manual I think needs some interpretation to become clearer...Trac Off mode, Auto LSD mode, VSC off mode. Am I supposed to advance from Auto LSD to VSC OFF mode when I am trying to get unstuck, which I seem to be reading is a 2 -step process? Am I close to understanding this?
  • wwestwwest Posts: 10,706
    The base problem arises from the fact that selective frictional braking is used to implement Trac, LSD, and VSC. If a condition requiring consistent, continuing, selective braking were to occur and the engine not be automatically dethrottled you would end up with warped brake rotors soon thereafter, or possibly engine failure of the drive train due to the extreme stress involved.

    Since the driver cannot be trusted to lift the gas pedal to the point of "feathering" when one of these modes activates the system does it automatically for you.

    So the only method for getting unthrottled wheelspin as a last resort to get unstuck, etc, is to disable ALL of these functions.
  • Ok, so I guess I forgot to turn my 4wd on once a month on my 2005 toyota sequoia. From what I read online it is in the owners manual. Would have been nice for the dealer to tell me that when I bought it. Now when I hit the button it just blinks on the dash and never locks in or changes. The dealer wants to charge 92.00 just to look at it. I read on this forumn about a fix for my back window (got the defrost and wiper working which is all I wanted, so thanks to all for that). Any idea on my new issue? Hoping there is a way to reset it or get it to engage without a dealer charge. I wasn't able to find anything online other than one guy who took it all apart and replaced a bunch of stuff. I am not mechanical but also not an idiot so I could do minor things.

    Please help as winter is here in Wisconsin.
  • wwestwwest Posts: 10,706
    edited November 2011
    It's sometimes easier for the 4WD clutch to "slip" into engagement accelerating, EASY acceleration, from a full stop, at a low speed, stopped, or even driving slowly, DEAD slow, in reverse.

    It's even worse if you have new tires at one end vs the other.
  • I have a 2003 4runner 4x4 v6 and just went through an ordeal with this but don't dispair. The problem lies in the actuator that is within the transfer case. It along with the front diff actuator are 9vdc and NOT 12vdc. This actuator inside the transfer case drives a pin that makes the transfer case go into 4wd high and then into 4wd low. The actuator is 1200-1300 alone. Aparently this is a weak link on these vehicles. I also am looking at a solution to this issue. For now I have a 4runner with this issue. With a lack of use the pin inside the transfer case becomes gummed up in its housing and gets stuck in one position or another. Mine was stuck in the 4wd low and required removal and rebuilding of the transfer case to free this pin. Sometimes a tap with a rubber mallet can free the pin but this didn't work for me. Good luck.
  • I am having the same problem... I have an 07 Highlander and the back has the 4wd emblem, however, there are no switches that indicate whether or not it is engaged. I recently had to drive through about 6 inches of snow, and I was all over the road, was kinda like riding a Squirrel. I also am not sure what the ect snow button does or does not do. When I had this turned on, the highlander was not any better driving in the snow.
  • Squirrels are agile creatures. Most of us would prefer a large squirrel in snow.
  • kyfdx@Edmundskyfdx@Edmunds Posts: 25,914
    And yet, squirrelly is a negative attribute, when it comes to vehicle handling characteristics... ;)

    Moderator - Prices Paid, Lease Questions, SUVs

  • wwestwwest Posts: 10,706
    Yes, about all you get with an HL F/awd is that emblem.

    The HL uses three fully "open", free-wheeling, diff'ls, front, center, and rear. The only time you will hav decent 4WD functionality is when all four tires have roughly equal traction......a whole lot of good that is.

    One wheel/tire loses traction and limits the engine drive torque to ZIP, ZERO.

    As of 2010 the RX350 adopted the new Venza F/awd technique, not as functional as would be the Honda/Acura SH-AWD system, but a substandual improvemnt none-the-less.

    In the class/price of teh HL look to the 4runner, R/awd, for a much more functional AWD/4WD system
  • Highlander has very effective AWD system that had proven itself to pretty much every HL owner. wwest never owned or rode a HL but has his own, not shared by anyone home grown conspiracy theories about Toyota AWD implementation in HL.

    HL doesn't have any switches to engage AWD, it on all the time. Use common sense, make sure that your tires are good and suitable for snow/all weather driving. If road really icy and slippery then no AWD in a world will compensate fully for hazardous road conditions. I own 2008 HL and really like 'snow' button functionality under heavy snow. It changes transmission shifting points so car feels more steady when accelerates on the snow.
  • wwestwwest Posts: 10,706
    edited January 2012
    Yes, I do not own an HL, but I do own the exacting(***1) equivalent, a 2001 F/awd RX300. Previously owned a 2000 F/awd RX300 which in retrospect I wish that I still had(***2). Due to pretty severe transaxle stress problems, premature failures, with the '99 and then less so the 2000 this early, more functional, F/awd system was abandoned. Those early failures proved to be the result of the rear drive being "automatically" engaged via the use of a VC, Viscous clutch/coupling design used to "lock" the center diff'l.

    By the time the HL went into production the F/awd functionality had yet again been lobotomized, the VC was eliminated entirely.

    "..home grown conspiracy theories..."

    For years now, 10 or so, I have paid the substantial annual subscription fee (techinfo.toyota.com) for full and complete access to ALL Toyota, Scion, and Lexus models. The information I publish here is derived directly as a result of my access to the appropriate factory service/shop manual set.

    If you suspect otherwise the daily access fee is quite affordable.

    "..it on all the time..."

    Pure BS. Anyone with even the most basic knowledge of AWD systems will understand that this just simply cannot be the case. Driveline components would be overstressed, so overstressed, that component failure would result within ~50 miles. Even "partially" automatically engaged, or even "part-time" automatic engagement is proving, right at this very moment, to be a problem with all reasonably functional F/awd system...the best of the best, the SH-AWD system, for instance.

    "..it on all the time..."

    No, it's ENABLED 100% of the time. The HL's F/awd system only activates AFTER-THE-FACT, only after FRONT wheelspin/slip is detected via simultaneous monitoring all four ABS "tone" wheels. And while one might think that the process of Trac activation would involve quick drive coupling to the otherwise "free-wheeling" rear tires. But due to serious safety concerns unique to FWD vehicles that is not the case.

    The first action taken via Trac activation will be braking of the front wheels in order to most quickly restore front traction and thereby alleviate the otherwise strong possibility of loss of directional control. To facilitate even quicker front traction recovery and to prevent overheating of those front brakes should the driver not quickly release the gas pedal the system will also automatically and simultaneously FULLY dethrottle the engine.

    Many later models, including the HL, using a F/awd technique of this type now have a Trac/VSC disable system so the driver might often have additional resources to get unstuck or initially moving forward on a slippery (uphill) surface.

    ***1 My '01 F/awd has an absolutely USELESS VC mounted across the center diff'l, purpose being to automatically "lock" the center diff'l under conditions of consistent wheelspin/slip. So useless that it was dropped entirely from the RX and HL with the advent of the RX330.

    ***2 My '00 F/awd RX300 not only had a fully functional VC, Viscous Clutch/coupling, it also had the then optional rear mechanical diff'l. I traded up to the '01 to get HID and VSC not realizing that I was giving a more functional, MUCH more functional, F/awd system.
  • You have wonderful theories but they proven to be baseless. Read actual HL owner experiences here

    linky

    We've been around this number of times. Just stop posting your useless technical mambo-jumbo and drive a HL in a snow for a change.
  • Looking for some opinions here. I'll be buying a Toyota soon (Land Cruiser, Tundra, or Sequoia) and have been debating between RWD and 4WD. I pretty much decided I have no need for 4WD here in TX. When I lived in the upper midwest, it always made sense to have the 4WD for the inevitable winter storms. In fact it was hard to find trucks and SUVs that were only RWD. Now that I'm living in TX I don't really see the need for 4WD yet I often see these trucks and SUVs optioned out with 4WD. Why? What am I missing? You add $3 -$4 grand to the price, add more items that could wear out or fail, and reduce the gas mileage. I've only been in TX a few years so maybe I'm missing something. Can someone tell me why I might need 4WD when living in the South?

    The only reason I can come up with is I may need it if I take winter trips to visit family in the UP or if I ever move back.
  • You might need 4WD to tow a future boat or travel trailer. If you ever decide to sell your vehicle, 4WD is like selling a house with a swimming pool. If the house is good, someone who must have a pool will buy your house over the one without. 4WD is great for off road, but if you have no desire.....not much point there. If you buy the vehicle without 4WD, you can never install it later, should your needs change. 4WD rarely goes wrong in Toyota's but, it does adversely affect the fuel mileage, by maybe 2 gpm's.
  • The thing you are missing, as you say, is this.......there is a huge community of "guys" out there who love to drive off road. If you want to drive in the bush, thru the muck, across streams, and generally cross country, then you have to have 4WD. I have a 4Runner, a serious off road vehicle. It has 4WD, with low and high and differential lock, it sits up high, and isn't too big, so I can get between trees in the woods. When I went to buy it, (used), there were a ton of 2WD's out there. I passed over all the 2WD's to find this 4WD. If your plan is to drive your vehicle to the office on the interstate, and you never plan to sell it, or move it back up north, then perhaps, your wasting your money on a 4WD.
  • Good points. I'm definitely not planning on moving north again, but of course never say never. I can see the need for 4WD for pulling a boat out of the water, but RWD for general towing on the highway should be fine. I'm leaning towards the Sequoia and I don't think too many people take them off-road since it's much bigger than your 4Runner. I also typically keep a vehicle for 10 years or more.
  • wwestwwest Posts: 10,706
    "...what am I missing..."

    How could you possibility miss the fact that you are now DEEP into Red-neck territory. Those 4WD/4X4 fully decked out trucks and SUVs, gun rack and gun included, are a societal requirement in your region. They may NEVER go off-road, off-road hunting, but they MUST look capable of same.

    You don't "need" anything beyond RWD. Travel back north, take tire chains along.

    My question would be why something as HUGE, weighty, and gas-guzzling as are your seeming choices. Wouldn't something in the 4runner class suffice?
  • "My question would be why something as HUGE, weighty, and gas-guzzling as are your seeming choices. Wouldn't something in the 4runner class suffice?"

    The answer is 3 teenage sons. The oldest is already 6'-4". The 4Runner doesn't get much better gas mileage and is much smaller. For basic trips, the 4Runner may be fine. For family vacations, it just won't cut it.
  • wwestwwest Posts: 10,706
    They why buy a huge gas-guzzler for the 96% of the time you're not on vacation...rent.

    Is the HL still available with the I4..?
  • "Then why buy a huge gas-guzzler for the 96% of the time you're not on vacation.."

    Because I can :) .
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