Hey all,

I have been asked by many people on other forums to explain the 4wd system of the '01-'02 4Runners 4x4 (also similar on '03 4Runner V6 models...see below). I just bought a '02 Limited 4x4, so i did some research and off-road testing on my new 4Runner.

Here is my take on it: (please correct any of it)

The 4Runner uses a 4-wheel-ABS-based traction control, called ActiveTrac (ATRAC for short). ATRAC is ALWAYS on, even in 2WD mode where it works on the rear axle.

Here are the different features of the 4Runner's 4wd system: (VSC is vehicle stability control)

(Note: read below for more info on HOW to engage the different modes)

1. 2WD mode: Rear wheel drive; switch to 4WD up to 62 mph.

2. 4WD HI: 4WD on any surface (full-time!), however, VSC is STILL active...thus, if you get stuck bad or climb a hill & slip, engine power will be cut because of VSC's inherent functions.

3. 4WD LO: 4WD with torque multiplication (2.57 times)...again, VSC is active. (read below on how to go to 4-LO)

4. 4WD HI with center diff LOCK: same as #2 but VSC is OFF, thus allowing you to spin your tires to get out.

5. 4WD LO with center diff LOCK: same as #3, but with VSC off.

To go from 2WD to 4WD HI, you push the 4WD button on the side of the transfer case lever, up to speeds of 62 mph. After pushing it, you are in 4HI and can go up to top speed on dry land with no damage.

To go from 4HI to 4LO, you need to stop the 4Runner...shift to NEUTRAL, then switch/push the transfer case lever to 4LO. Then, you put the transmission back into DRIVE.

To LOCK the center differential (thus, TRUE 50/50 power split between front and rear axle), you need to push the button to the left of the steering wheel on dash. This should be done only on loose terrain (because of 50/50 split) to prevent binding of the center differential. Again, this will disable the VSC, allowing you to power through mud (which you cannot do effectively if VSC is ON).

In reality, the MAIN reason most people LOCK the center diff in the 4Runner is to turn OFF VSC. Very few off-roaders (esp. beginners) will ever see the need of the true 50/50% split. An example is if BOTH your front (or rear) wheels or 3 wheels are in mud (no traction)...in which case, locking the center diff is a good thing because it allows 50% of power to be routed to the AXLE that still has the wheel(s) with traction. Without the center diff LOCK, 100% power will be routed to the axle that has both wheels slipping (thus, you are stuck). However, this is rarely encountered in off-roading.

SUMMARY:
1. 4runner ('01-up) has 4-channel ABS system
2. It has VSC (stability control) and ATRAC (4-wheel traction control)
3. No rear locker
4. You can switch into 4wd (4-HI) at any speed up to 62 mph
5. You can drive in 4wd all day long at any speed
6. You can switch from 4wd to 2wd at any speed
7. But you do NOT want to lock the center diff on dry pavement...this is ONLY done off-road or on slippery ground.
8. Locking the center diff shuts off VSC (stability control), which is a good thing in off-roading. VSC tends to kill momentum when you're slipping & sliding and this is not desired in off-roading (under most circumstances)
9. ATRAC is always ON. In 2wd mode, it works on your rear axle. In 4wd mode, it works on front and rear axles
10. So, you have several modes: 2wd...4-HI...4-HI center diff LOCK...4-LO...4-LO center diff LOCK.

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For 2003 and up, V6 & V8 4Runners have a Torsen center diff (Torsen T-3 design) that is lockable (true 50/50 split). V8 model has full-time system (no 2wd mode). V6 model has an additional option of 2WD. It is basically a full-time system that varies torque transfer to the front and rear axle according to amount of slippage. Prior to 2003, the torque split was 50/50% most of the time (center diff unlock). I believe the Torsen provides more stable handling (due to torque variations) in slippery conditions. The above description applies for 2003 4Runners with V6 4wd system.

The 2003-up V8 models have a full-time 4wd system similar to Toyota Land Cruiser, Lexus LX470, and GX470. With this system, the 4runner is ALWAYS in 4wd Hi mode (center diff can be locked or unlocked). There is also a 4-LO range.

Hope this helps.