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4WD and AWD systems explained

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  • ccaywoodccaywood Los AngelesPosts: 1
  • paisanpaisan Posts: 21,181
    My guess is that you definitely damaged the 4wd system when you wrapped that pillow up in it. Seems to be the only logical explaination of it.

    -mike
  • russlarussla Posts: 74
    Hi Mike, are you still maintaining your Isuzu page?

    Thanks

    RLR
  • paisanpaisan Posts: 21,181
    It's just down right now, should be up shortly.

    -mike
  • Hello -

    I have a 2005 tribute with electronic 4wd. The 4wd light came on and my seat heaters stopped working after my last windshield wiper control repair, leading me to believe its just a fuse. Right now the 4wd indicator light blinks 3x/minute, which means that it needs service, but does anyone know if the electronic 4wd will still function if its simply an electrical/fuse problem?
  • ateixeiraateixeira Posts: 72,587
    I'm not sure, but the fuse theory seems feasible since it is controlled electronically (vs. mechanically).

    -juice
  • mamb99mamb99 Posts: 1
    The 4x4 lights on the instrument panel blink 3 times every few minutes. Does anyone know what this might mean. Also I was wondering if anyone knows how to find the original code for the keyless pad. I heard it was on the computer module but not having any luck. Thanks.
  • tejayntejayn Posts: 1
    I have a 2002 ford explorer. its an automatic with the 4.0 and automatic four wheel drive. the 4x4 high light on the dash flashes 7 times every few minuets and the four wheel drive is intermittently engaged. I have hooked it up to a scanner but i cant get into the four wheel drive system. any ideas or advise would be appreciated.
  • ryan07ryan07 Posts: 1
    My 2000 Nissan Pathfinder 4WD system has recently been causing problems. It is slow to engage and the only way to disengage it is to shift the 4wd lever into 2wd and then shift the transmission into reverse and 'goose' the gas. Any suggestions as to what the issue may be?

    Thks
  • reading your situation with your 2004 was like i wrote it. i just bought a 2004 yukon with stabilitrack, the dealer was confused as i was. have you fiqured out how to use? the manual was very confusing. thanx
  • alexstorealexstore Posts: 264
    can someone explain Highlander's Hybrid 4WD system compared to regular 4wd Highlander?
  • ateixeiraateixeira Posts: 72,587
    Yes, but surprisingly, it's based on the FWD Highlander.

    Basically, only the front axle gets power from the engine. There is no driveshaft going to the rear.

    The rear axle is powered by electric power only. The electric assist goes to both axles, funny enough.

    So the gas engine is FWD and the electric boost is what makes it AWD.
  • alexstorealexstore Posts: 264
    so basically 4wd is limited till what speed?
  • ateixeiraateixeira Posts: 72,587
    I'm not sure if it is speed restricted. Presumably you'd get an electric boost at any speed if you floor it (passing on a highway, for instance).
  • steverstever YooperlandPosts: 40,209
    I think this video just about sums AWD up:

    AWD Technology

    Moderator
    Need help navigating? stever@edmunds.com - or send a private message by clicking on my name.

  • ateixeiraateixeira Posts: 72,587
    Love the use of duct tape...
  • I have a 1998 Ford Explorer and it makes a weird winding noise when turning. At first I was thinking it was the power steering but my mechanic thinks its the AWD unit. It seems like my gas mileage has drastically dropped so I am also thinking its the same. It almost seems as though the AWD is constantly locked in because when you turn it also gets very rigid. Have you ever heard of this happening and is this possibly a recall item I dont know of. I'm sure it will be astronomical to fix this if it is the AWD...and the noise is driving me nuts. Not to mention I dont know if it dangerous to keep driving it like this or if it is doing more damge.
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,406
    One easy way to distinguish between the steering or the AWD "whining noise" is to turn your wheels side to side while stopped. If you get the same whining, it is the power steering pump. Aerostar vans are notorious for whining power steering pumps. The pumps work fine, but they sure to whine about it!

    As for AWD, I expect that the Exploder probably has a part-time, electronically controlled system. The Ranger has a switch-controlled electronic 4WD system that has all sorts of problems with the electronics. If the Explorer shares components in its system, it could be that the AWD is engaged all the time due to some system failure. Is there a light on the dash that will typically let you know when the system is engaged? As the system is part-time, it is likely hard on it to be running on dry pavement, etc., due to the lack of slippage available. If you turn hard at slow speeds, you should be able to feel the truck "binding" a bit and likely hear wheels slipping as the system relieves pressure. Try it on a gravel surface so the wheels will let loose easier.
  • What really happens is when you're driving it feels like the feeling you get when engauged in 4 wheel drive. The steering gets rigid and jumpy. Especially when on the highway and you hit a bump doing like 55-65 MPH. The whole front end gets a massive vibration and pulling. It also feels like the steering wheel is drifting side to side. I firmly believe its the AWD locked in constantly....although it started gradually happening and stopping but now doing it all the time. It feels very dangerous and my gas mileage is terrible. I'm sure this is a ridiculous price tag to fix if not a reacll item.
  • ateixeiraateixeira Posts: 72,587
    I know they used to have a viscous coupling, but can anyone tell me what Toyota is using for the current models?
  • I have a 96 Cherokee. Only recently have I had the need for 4WD. I have heard a faint whining sound when engaged in 4WD and driving, that stops when the car stops. Now, the car seems to be in 4WD, even when I switch it back to 2WD. After a bit, I'll hear a "thud" and can feel it disengage, and then I am definitely back in 2WD. What's happening here? It's only happened twice, both today. Its cold and snowy where I am. I don't want to ruin anything. Any thoughts?
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,406
    It is probably worth your while to check the fluid levels in both the transfer case and the front differential. If you have never replaced it, consider doing so now. It sounds to me like something is binding a bit - probably in the transfer case - and preventing the system from disengaging. Also, are you engaging and disengaging it properly? Some of the "older" shift-on-the-fly systems (not sure if Jeep falls under this classification) required a short jaunt in reverse to allow the transfer case to disengage, even though you can shift into 4WD while traveling forward.

    Any problems with it engaging at the time you request it?
  • Thanks much for the reply. I've had no problem engaging whatsoever. I'll replace the fluid tomorrow. I'll try reversing first to disengage as well and will post results.
  • Glad to have found this forum as I have some AWD queries:

    1. Is it possible to change the Subaru Outback auto-trans AWD bias ? I understand it is RWD-biased and perhaps that is why the car has a reputation for spinning out (per CU and some other tests I have read) ? Would be nice to be able to readjust it to prevent that.

    2. How does the RAV4's AWD compare to the Outbacks? It seems the RAV4 is reactive, save for a user setting that offers full AWD for speeds below 20 mph.

    I'm also curious if VW has abandoned the torsen based Quattro and is now relying on Haldex, and how the Haldex system compares to that used in the Subaru.
    :shades:
  • ateixeiraateixeira Posts: 72,587
    I'll take a shot at trying to answer each question.

    1. Not really, though you can insert a FWD fuse to send all power to the front axle. Note that this is for temporary use only, such as when you get a flat tire.

    2. I was bummed that Toyota took away the full-time system that existed in prior RAV4 models. The new one is part-time, on-demand. At an event Toyota hosted themselves, the AWD system failed to climb a hill they had picked for their press demo:

    http://www.drive.com.au/Editorial/ArticleDetail.aspx?ArticleID=11004&vf=23

    VW: Haldex makes what is probably the quickest reacting AWD system on the market, but it's still reactive. Volvo and Ford also use the same supplier for their systems.
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,406
    The AWD on the Subaru automatic actually defaults to a FWD bias, though it can shift to rear depending on the traction situation, as much as 80-20 either way. But no, it is not driver controllable. The STi has a driver-adjustable system, at least on the new model.
  • paisanpaisan Posts: 21,181
    Not anymore Wes. The new 5EATs are 45/55 torque split. The 4EATs are 80/20.

    -mike
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,406
    Ah, so while the 4EAT sticks with the FWD bias, the 5s (in... XT and H6?) are slightly RWD bias. What is the variability allowed in the center differential on the 5EAT to shift power based on traction?
  • ---and now Saab uses Haldex in a very complex new system. Unfortunately (your mileage may differ !!) that vehicle is tuned for the track, not all around use.

    Interesting article about the RAV4. Does not inspire confidence. Did Toyota change anything for '07 or are they using the same system?
  • ateixeiraateixeira Posts: 72,587
    No change as far as I know.
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