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Toyota 4WD systems explained



  • wwestwwest Posts: 10,706
    The MAF/IAT module is mounted on top of the air intake just downstream, toward the engine, of the intake air filter.

    Unplug the connector with the engine idling, the engine will die, reconnect the MAF/IAT and restart the engine and be on your way. CEL will extinguish maybe as few as 3 restarts of the engine depending on the range of operations, city/hwy/etc, in the interim.

    ABS will continue to be enabled throughout.
  • briegelbriegel Posts: 139
    I posted this about a week response yet. Anyone have some thoughts?

    ********************************************************************************- **************

    I have a 2005 RX 330 AWD. What are the concerns with coasting downhill in NEUTRAL at speeds ranging from 25-70 mph to save fuel? Potentially damaging to the transmission and/or the AWD system? Thanks!
  • tidestertidester Posts: 10,110
    In addition to possibly being illegal, there are safety concerns. Besides, you're not really using all that much fuel driving downhill in gear anyway. The ECU senses the load on the engine and adjusts the flow of fuel accordingly.

    tidester, host
    SUVs and Smart Shopper
  • briegelbriegel Posts: 139
    Thanks for the reply. You are probably right, but the engine rpms do drop down to the idle range when coasting in neutral. However, I was told that the transmission fluid pump shuts off when in neutral so the fluid is not circulating through all the moving parts which could cause wear and damage...that is what I was mainly concerned about. Any thoughts on that?
  • tidestertidester Posts: 10,110
    If that's true then it would be a concern. Perhaps someone with knowledge of Toyota transmissions will chime in. Anyone?

    tidester, host
    SUVs and Smart Shopper
  • wwestwwest Posts: 10,706
    The gear type ATF pump is driven directly by the torque converter, if the engine is turning the pump is pumping...
  • I just bought a 4WD auto FJ which I'm loving so far. My salesman told me that I shouldn't use my 4WD for the first 5,000 miles--I've NEVER heard of this and need some other opinions... help! Thanks so much! (of course, I'm eager to take it out onto my property to do some hills, etc. to see how it does)
  • newdavidqnewdavidq Posts: 146
    The owners manual is always the best place to find answers. Your salesman is misinforming you (to put it nicely). I have a 4wd 4runner and the only restriction I noted when it was new last year was to not do any towing for the first 500 miles.
    Hope this helps.
  • Last winter I lost traction & control coming down from the mountains in modestly icy conditions; speed was moderate; was surprised since I was in permanent (AWD) 4WD-High with VSD "on." Have Michelin Cross Terrain tires in very good condition. Was surprised to have lost complete control given the 4Runner's good reputation for these conditions. I have the V8 with full-time AWD (High/Low gear range switch selectable).

    What is the best 4WD configuration to be in in these conditions? (I thought about locking the differential but then you lose VSC - i.e. VSC turns off when you lock the differential, as I understand it)

    Thanks for any advice from other newer 4Runner drivers,

  • wwestwwest Posts: 10,706
    As a general rule you should NEVER use anything but RWD mode once underway at even moderately low forward speeds. This is especially true going mostly downhill.

    Remember that your traction coefficient with the roadbed does NOT change as a function of RWD/AWD/4WD/4X4 mode, only the efficiency with which you USE the available traction changes with drive configuration.

    4 wheel drive mode, like FWD or F/AWD, can be of great help getting up and going initially on a slippery or low traction surface, but can turn HAZARDOUS very quickly once underway. Again, most especially so, HAZARDOUS, on a slippery downhill drive.

    "I have the V8..."

    Even with the V6 you should never, NEVER, manually downshift the transmission for engine compression braking when on a questionable traction surface and in any "4" wheel drive mode. VSC does NOT have the ability to alleviate stability problems resulting from engine compression braking. Were I you I would even go to whatever extremes might be necessary (shift into neutral..??) to prevent even an automatic downshift in the conditions you describe.

    Oh, one other thing, in the conditions you describe the judious/careful/slight use of the rear implemented parking, e-brake, can oftentimes be of great help as an aid to keeping your speed low enough for conditions without threatening loss of control via "normal" front biased frictional braking.
  • Thanks for your response to my question about 'best 4WD configuration' going downhill in slippery conditions....having lost control last year in such conditions, I'd like to be better informed this year.

    You suggested "RWD only" mode for such conditions. I don't have "RWD only" in my '04 4Runner. It is 'AWD all the time' with options for low range of course, as well as for locking the differential. Given these alternatives, I can lock the diff. and turn off VSC or not lock the differential and drive with VSC "on." Either way, I'll just have to slow way down given the propensity of the car to break loose.
  • wwest probably misread your post. In your case, the standard AWD unlocked is the way to go. The vehicle lost traction because of the tires. If you live where snow and ice are a seasonal issue, then consider snow tires. A second consideration is an all-weather tire like the Nokian WR S.U.V. AWP that can be run year round.

    If snow and ice are not normal conditions and this was a one-off deal, then avoid driving in those conditions with the Cross-Terrains, or chain up. It was the tires losing grip that caused loss of control. Snow tires have softer tread and many sipes allowing the tire to flex and grip.
  • nedzelnedzel Posts: 787
    4WD isn't magic. It can't increase your coefficient of friction. It helps you go. It doesn't help you stop or turn.

    Michelin Cross Terrains are fine all-season tires. I've got a set on my 2003 4Runner. I only use them in the summer. In the winter I mount a set of snow tires. Real, honest-to-goodness snow tires. You may be surprised at the difference in performance in slippery conditions between all-season tires and snow tires.

    If you are driving too fast for conditions, no 4WD setting is going to help you.
  • The cause (and solution) being the tires makes sense. Was searching for a holy grail in the vaunted Toyota 4WD system that wasn't there. Thanks for your insight!
  • wwestwwest Posts: 10,706
    The holy grail is called VSC + A-TRAC.
  • nedzelnedzel Posts: 787
    "Was searching for a holy grail in the vaunted Toyota 4WD system that wasn't there."

    Toyota's 4WD system is better than most, but 4WD helps you go. It doesn't help you turn or stop. Think of it this way - your brakes stop your tires, but your tires stop your truck.

    One problem with all 4WD systems, particularly good ones, is that they can give you overconfidence in slippery conditions. Back when I grew up, driving a '70 Ford station wagon in the snow, I knew just how slippery the road was. Each time I accelerated (even gently) in snow, the rear tires would slip. That continual reminder of how slippery it was caused me to drive slowly and carefully.

    My 4Runner seldom slips in the snow when accelerating, so I don't get that constant reminder to slow the heck down. Whenever I am in snow, as soon as there is no traffic behind me I brake quickly to test the traction.

    4WD is not magic. Which is why you often seen SUVs sliding off the road during a snow storm.
  • tidestertidester Posts: 10,110
    Which is why you often seen SUVs sliding off the road during a snow storm.

    That may be because the only vehicles on the roads during a snow storm are SUVs. :)

    tidester, host
    SUVs and Smart Shopper
  • other1other1 Posts: 7
    That's sort of not necessarily true. Most rides are only as good as the tires it has. I've seen SUVs that can't get out of their own way in the snow where a FWD with snow tires goes right through it. Tires are everything in the snow.
  • tidestertidester Posts: 10,110
    I agree on your point about the tires. However, I suspect that when the weather gets really bad you're likely to see mostly people with 4WD vehicles brave enough to venture out. That stacks the deck in favor of 4WD vehicles slipping off the road compared with FWDs or RWDs.

    tidester, host
    SUVs and Smart Shopper
  • nedzelnedzel Posts: 787
    Actually, some of the times I've seen the most SUVs off the road has been during snow storms at rush hour. Everyone was "going out" in the snow simply because we had to to get back home. So there really was little self-selection going on. Back when I had a FWD car with snows (GTI), I routinely passed such trucks. As did my wife in her C240.

    I think part of the reason is poor education on the part of the drivers, but also, I as posted above, over-confidence. The extra traction that 4WD gives you when accelerating makes it easy to overestimate how much cornering and braking performance you really have.
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