Question r/e diff. slip when backing downhill then starting forward uphill and 4wd...

[jcage89]

Hi,

I have an 06 V6 4wd Sport and have experienced the issue of the slip indicator (squiggly lines) flashing along with beeps and clicks when I back out of my driveway (downhill) and then put it into drive and attempt to resume forward on the street (uphill). This phenomenon is discussed in the follwing thread which attributes the issue to the Hill Assist Control (HAC) kicking in...

http://www.toyota-4runner.org/showthread.php?s=&threadid=2292&highlight=slip+indicator

A review of the manual reveals that the HAC should only engage from a stop on a hill to hold the truck's position for a few seconds until the accelerator is depressed. This should only happen when the break is released and the 4runner is in a fwd gear. I have tested the HAC as described in the manual and verified it to work. For example, if I am traveling forward, come to a stop on an incline and then remove my foot from the break, then the 4-runner will not roll backward while I am moving my foot to the gas. This works fine and I am allways able to move forward uphill without losing power or rolling backward.

Conversely, when rolling backward out of the driveway and then trying to go forward, I experience the slip light, beeps and clicks. But then I also continue to roll back slightly and have no forward power (just clicks and revs). If I release the gas, hit the break and then try again, the slip goes off and I am able to resume uphill. This does not seem like the HAC system working to me, but rather the ATRAK or VDC truly slipping and losing forward driving power for a few seconds.

Any others ith more experience on this issue? Also, reading the manual thoroughly can get confusing when it comes to the acronyms used by Toyota. I understand what differential does in both 2wd and 4wd and why to lock it in certain offroad 4wd situations, but I am slightly confused about the following...

Is Acitve Traction Control System the same as ATRAC and how is this different from VSC?

pg 173 of the manual says to "leave the ATRAC system on while dirving in normal conditions.." which is confusing because I didn't know you could turn it off? I understand you can override VSC by locking the center diff. but do not know any other way to defeat ATRAC or VSC?

What is Automatic Disconnecting Differential (A.D.D.) referenced on page 169 of manual? Manual says it can be engaged or disengaged by shifting procedures but then doesn't explain what it is. I assume it just means enaging and disengaging the front diff. automatically when moving from H2 to H4 and visa versa.

Do you really need to drive 10 miles per month in 4wd to keep the system lubricated? I have had multiple 4wd SUV's in the past and never knew this was a requirement. I only use it rarely when mtn biking or skiing.

Sorry for the long post, but if anyone can shed light on some of this, would be appreciated.

-JC

 

[OUTRNNR]

Sounds to me like your HAC is functioning properly, there have been many people around here (myself included) who have stated that the HAC system activates if you shift from reverse to drive too quickly while rolling backward. No one really knows what systems are at work when this happens (VDC, ATRAC, ABS, etc.) but if you take more time to shift into drive allowing the car to stop before engaging drive then the vehicle won't fuss about it.

ATRAC is Active Traction Control. It uses the 4 channel ABS to individually brake a spinning wheel to transfer torque to a wheel with more grip, in a sense it acts as a virtual LSD. VSC is Vehicle Stability Control. It also uses the 4 channel ABS but instead of providing traction, its primary function is to keep the vehicle in control by braking certain wheels to counteract oversteer or understeer. Locking the Center differential will turn off VSC, but not ATRAC, I have been under the impression that ATRAC cannot be turned off on the 4Runners, so maybe the statement in the manual is a little off.

I have no idea what an automatic disconnecting differential is, but you description you provided sounds like it could be correct. And, yes, you should run the vehicle in 4WD every once in a while to keep the system lubricated, but I'm sure if you didn't, it would still function just fine...

Hope this helps, if anyone notices an error in anything I typed please feel free to correct me