4WD, Lock Button, VSC Off Button and DAC Button - How They Work - Toyota RAV4 Forums
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post #1 of 29 (permalink) Old 02-18-2014, 07:26 AM Thread Starter
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4WD, Lock Button, TRAC Off Button, DAC Button and HAC/HSA - How They Work

As there seem to be quite a few questions lately about the drive control systems and buttons on the 4.3 RAV4, I thought I would create a thread for the specific purpose of providing an overview explanation of these systems. Maybe it could become a "sticky?"

I'll start with how I understand the systems to work, at least for North American models, and others can please chime in with additional information. I'll edit this first post with additional information as appropriate.


4WD System ("Active Torque Control" System)
The 4WD system on the 4.3 RAV4 is called "Active Torque Control." In the 4.4 RAV4 it got renamed to "Dynamic Torque Control" but it is the same system with the additional awareness of Sport mode, which was new on the 4.4 models.

Under normal circumstances the 4WD RAV4 operates in front wheel drive mode for increased fuel efficiency, with the rear wheels getting some portion of power only when it is detected this is beneficial to the vehicle. For example, if the front wheels start to slip. I've read that the detection process typically takes something on the order of 6 milliseconds.

Here is the ATC description from page 194 of the 2012 RAV4 owner's manual:

Automatically switches from front-wheel drive to four-wheel drive (4WD) according to the driving conditions, helping to ensure reliable handling and stability. Examples of conditions where the system will switch to 4WD are when cornering, going uphill, starting off or accelerating, and when the road surface is slippery due to snow, rain, etc.

A much more in-depth description of the 4WD system in the RAV4 can be found in this Toyota document (thanks, JuneBug!)

This link from Toyota allows interactively exploring the various 4WD systems they offer, including for the RAV4: http://www.majormedia2.com/4WDSimplifiedv5/4WD.html



TRAC (Traction Control)
This is one of the so-called "nannies" which may reduce power to the wheels. The 2012 RAV4 owners manual has this to say about TRAC:

Maintains drive power and prevents the drive wheels from spinning when starting the vehicle or accelerating on slippery roads.

This will reduce power to slipping wheels in order to improve the odds that they'll be able to get traction.


VSC and Enhanced VSC (Vehicle Stability Control)
These are more of the so-called "nannies" which may reduce power to the wheels. The 2012 RAV4 owners manual has this to say about VSC and Enhanced VSC:

VSC - Helps the driver to control skidding when swerving suddenly or turning on slippery road surfaces.

Enhanced VSC - Provides cooperative control of the Anti-lock Brake System (ABS), TRAC, VSC and Electric Power Steering (EPS). Helps to maintain directional stability when swerving on slippery road surface by controlling steering performance.

This is accomplished at least in part by using accelerometer sensors in the front and rear of the vehicle and sensors in the steering. If the accelerometers indicate the vehicle is not moving in the direction the front wheels are pointing (e.g. the vehicle is yawing) this system will kick in to control power to various wheels to help the vehicle move in the direction the steering is pointing.


DAC Button (Downhill Assist Control, located to the left of the steering wheel)
This button is used to turn on or off the DAC system, which is available only in the 4.3 models with the V6 engine and all 4.3 models with the 3rd-row seat (as of this writing it's not available on the 4.4 models). This system, which some have hailed as little short of miraculous, forces the vehicle to crawl down a steep/slippery hill at approximately 3 MPH (5 KPH) by individually applying varying brake pressures to each of the 4 wheels.

This system can only be turned on when the vehicle is moving at less than 15 MPH (25 KPH) [stopped is preferred?] and the shift lever is either in L (low) or R (reverse). When on, the DAC light on the dashboard will light up steady. If the DAC button is pressed while using the system, the light flashes and the system gradually ceases operation. The light will go out when the system goes off.

The system will automatically turn off if:
- The brake pedal is depressed
- The accelerator pedal is depressed

From the owner's manual, here is what the DAC button and instrument panel light look like:



4WD Lock Button (Located to the left of the radio)
When pressed, the Lock button "locks" power 55% to the front wheels and 45% to the rear wheels at speeds up to 25 MPH (40 KPH). A light on the dashboard stays illuminated when this system is manually turned on, and goes off above 25 MPH to indicate the system is off, or if the button is pushed again to turn it off. If this light ever flashes, it means there is a problem with the 4WD system.

While the owner's manual states that the system will turn off if the brakes are applied "to ensure the ABS and VSC systems operate effectively," this does not appear to be the case in my RAV4. I tested it today, and the lock stayed on when I pressed the brake pedal.

This button is primarily intended for the driver to help get the vehicle unstuck. The RAV4 has no way for the driver to force the system to continuous 4WD mode at speeds above 25 MPH. While this is ostensibly to maintain increased fuel economy, some have theorized it's also to prevent over-stressing the components with the shock loads that could occur at higher speeds.

From the owner's manual, here is what the 4WD Lock button and instrument panel light look like:


TRAC Off Button (Located in front of the front left cup holder, 2009 and newer models)
Pressing this button momentarily will turn off the traction control system. When off, the "TRAC OFF" indicator light will appear on the dash. Pressing the button again will reactivate the TRAC system. The TRAC system will come back on automatically when the vehicle speed increases, or the vehicle is restarted.

Pressing and holding this button for a few seconds while the vehicle is stopped will turn off both the TRAC system and the VSC system. The "TRAC OFF" and VSC Off indicator lights will appear on the dash. Pressing the button again will reactivate these systems. These systems will also come back on again the next time the vehicle is restarted, but neither will come back on if the vehicle speed increases.

From the owner's manual, here is what the TRAC Off button looks like, as well as the lights for both TRAC Off and VSC Off:

To accomplish this for 2006 - 2008 models, a process affectionately known as the "brake dance" must be used.


What to do if stuck in snow or mud, or to help prevent getting stuck
If stuck in snow or mud, generally the best thing to do is turn on the 4WD Lock system and turn off the nannies (both the VSC and TRAC systems), as described above. Turning the nannies off, particularly TRAC, allows rocking back and forward to more forcefully to get unstuck.

Though as Dr. Dyno recently stated in another post (click here for full context): The 4WD systems in our RAV4s aren't heavy duty like a 4X4 truck so be careful when disabling the electronic nannies, part of whose purpose is to protect the lighter duty components. That's probably also why 4WD LOCK goes off at 25 mph.


Hill Assist Control (HAC) (Using the brake pedal)
This system is also sometimes called Hill Start Assist (HSA). The owner's manual has this to say about HAC:

Hill Start Assist Control (HAC) is designed to help minimize backward rolling on steep ascents.

This allows the driver to move their foot from the brake pedal to the gas pedal without the vehicle rolling as they are moving their foot.

HAC can be activated by very firmly pressing the brake pedal for a few seconds. A single beep and flashing indicator on the instrument panel will indicate the HAC system is active. When the driver eventually lifts their foot off the brake pedal, the brakes will remain engaged for 2 to 3 seconds and will then release, allowing the vehicle to move. A single beep is heard when the brakes release and the light on the instrument panel will turn off. Here is a YouTube video demonstrating HAC in the RAV4.

From the owner's manual, this light (the same as the VSC light) will appear on the instrument panel when HAC is being used:



Much more in-depth descriptions of the ABS, VSC, TRAC, EBD, HAC, DAC and Auto LSD (for 2WD RAV4s) can be found in this Brake Control System document. (Thanks again, JuneBug!)

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post #2 of 29 (permalink) Old 02-18-2014, 08:00 AM
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Quote:
Originally Posted by DVS View Post
DAC Button (Downhill Assist Control, located to the left of the steering wheel)
This button is used to turn on or off the DAC system, which is available only in the 4.3 models with the V6 engine and all 4.3 models with the 3rd-row seat (as of this writing it's not available on the 4.4 models)
Good and useful post, thanks! However, my 2007 4.3 4-cylinder does have that DAC button as well - yet no 3rd row seat. Might be because it's the European model . .
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post #3 of 29 (permalink) Old 02-18-2014, 08:04 AM Thread Starter
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Originally Posted by Nosegear View Post
Good and useful post, thanks! However, my 2007 4.3 4-cylinder does have that DAC button as well - yet no 3rd row seat. Might be because it's the European model . .
Excellent point! For now, I have clarified in the original post that the information is tailored towards North American models, but obviously how the systems work (the main point of the post) should be the same regardless of the market for which the RAV4 was made.

Thanks!

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post #4 of 29 (permalink) Old 02-18-2014, 09:34 AM
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DVS, an excellent write-up! A couple of clarifications from my experience & testing.

On DAC: If you have the button you have it. But 99.9% of owners would never get into a situation where it's needed. Probably why it was omitted of the 4.4s as the ruggedness of the original RAV4 has gradually been drained out.

The DAC button could be left ON full time but would never activate in any on-road situations I could imagine.
It will not activate above the very slow speeds mentioned or on anything but steep terrain, pretty much places you shouldn't be. The exception might be driving down a steep slippery driveway. Even then w/o practice it would be hard to take you foot off the brake to activate it when you think you'll be sliding into a ditch. For anyone who might get into that situation I highly recommend trying it in the dry if not as practice for when you might need to rely on it, then just to hear the wonderful hydraulic noises it makes.

On the 4WD button: Some of this comes from viewing the LED I have connected to the drive signal to the electro-coupler and some from testing on dirt roads with V6 power.
Quote:
This button is intended to help get the vehicle unstuck.
Somewhat misleading as it'll activate 4WD automatically w/o pushing the button.
Quote:
The RAV4 has no way to force the system to 4WD mode at speeds above 25 MPH.
Definitely inaccurate, at least as written and contradicts, "Under normal circumstances the 4WD RAV4 operates in front wheel drive mode for increased fuel efficiency, with the rear wheels getting some portion of power only when it is detected this is beneficial to the vehicle." If all 4WD shut off above 25 mph my front tires would lose traction at that speed with 269 HP driving only them. My dirt road testing showed the LED staying bright until 40 mph. I suspect on snow it would come on at even higher speeds but I don't have a frozen lake around here to try it on.
Quote:
While this is ostensibly to maintain increased fuel economy, some have theorized it's also to prevent the 4WD system from overheating.
It certainly is for fuel the economy benefits of front wheel drive over full time AWD. That's one reason I switched from Subaru to Toyota. I'd call it to prevent over-stressing the components with the shock loads that could occur at higher speeds. Overheating would apply to systems with viscous couplers.

BTW, I was going to give you a "Thanks" but it'll be deleted if you edit the post so I'll let things "settle out" first.

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It's the pedal (or the handgrip) on the right!!


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post #5 of 29 (permalink) Old 02-18-2014, 10:29 AM
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Even tho it's not a "button" per se, it would be nice to have hill-start assist listed in here too!
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post #6 of 29 (permalink) Old 02-18-2014, 01:05 PM Thread Starter
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Quote:
Originally Posted by Dr. Dyno View Post
DVS, an excellent write-up! A couple of clarifications from my experience & testing...
I reworded a couple of clarifying things (in bold):

This button is primarily intended for the driver to help get the vehicle unstuck. The RAV4 has no way for the driver to force the system to continuous 4WD mode at speeds above 25 MPH.

This sentence now reads as thus:

While this is ostensibly to maintain increased fuel economy, some have theorized it's also to prevent over-stressing the components with the shock loads that could occur at higher speeds.

Thanks very much!

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post #7 of 29 (permalink) Old 02-18-2014, 01:35 PM Thread Starter
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Quote:
Originally Posted by EatSleepRavRepeat View Post
Even tho it's not a "button" per se, it would be nice to have hill-start assist listed in here too!
Thanks for the idea!

I think it's a good idea, and have just added a section for it and updated the thread title accordingly.

Also, I'm thinking about adding images of:
- The buttons
- Their locations
- The Instrument panel lights

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post #8 of 29 (permalink) Old 02-18-2014, 03:57 PM
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Quote:
Originally Posted by DVS View Post
As there seem to be quite a few questions lately about these systems and buttons on the 4.3 RAV4, I thought I would create a thread for the specific purpose of explaining these. Maybe it could become a "sticky?"

I'll start with how I understand the systems to work, at least for North American models, and others can please chime in with additional information. I'll edit this first post with additional information as appropriate.
.
This Toyota document provides a great overview of how the 4WD system works:

4wd System Description 103kb PDF

And this Toyota document explains in great detail how the ABS, VSC, TRAC, EBD, HAC, DAC, Auto LSD, and Brake Assist work:

Brake Control System 591kb PDF

Help RAV4World members help you by providing your car's operating location in your profile page. Climate can cause a RAV4 in Dallas Wisconsin to experience a different set of issues when compared to the same model in Dallas Texas.
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post #9 of 29 (permalink) Old 02-18-2014, 04:01 PM
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Excellent post! I like the idea for photos of buttons, too. It's very helpful to summarize some of the stuff that might get lost in the owners manuals. If you are new to the RAV 4WD, good luck having the salesman or service dept help you with explanations how it works in various scenarios.

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post #10 of 29 (permalink) Old 02-18-2014, 04:19 PM Thread Starter
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Quote:
Originally Posted by JuneBug View Post
This Toyota document provides a great overview of how the 4WD system works...
Hey JB...thanks for those links! The idea behind this post was just to give a high level summary of these various systems all in one place, in fairly simple terms, without having to go through lots of detailed manufacturer documentation.

But it's great to have those links as references in this thread.

I may try to incorporate the links into the original post, to provide those who want more depth an easy way to find it.

Thanks again.

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