ABS, TRAC, VSC and Auto LSD

Squid · #1 (**permalink**) 08-08-2007, 10:16 AM

Chicks has got me on a mission so I thought I'd share what I've dug up so far.

ABS Operation
This system controls the respective brake fluid pressures acting on the disc brake cylinders of the right front wheel, left front
wheel, and rear wheels when the brakes are applied in a panic stop so that the wheels do not lock.
This results in improved directional stability and steerability during panic braking.
1. Input Signal
(1) Speed sensor signal
The speed of the wheels is detected and input to TERMINALS FL+, FR+, RL+ and RR+ of the skid control ECU with
actuator.
(2) Stop light switch signal
A signal is input to TERMINAL STP of the skid control ECU with actuator when the brake pedal is depressed.
2. System Operation
During sudden braking, the skid control ECU with actuator which has signals input from each sensor lets the hydraulic
pressure acting on each wheel cylinder escape to the reservoir.
The pump inside the skid control ECU with actuator is also operating at this time and it returns the brake fluid from the
reservoir to the master cylinder, thus preventing locking of vehicle wheels.
If the skid control ECU with actuator judges that the hydraulic pressure acting on the wheel cylinder is insufficient, the current
acting on the solenoid is controlled and the hydraulic pressure is increased.
Holding of the hydraulic pressure is also controlled by the ECU, by the same method as above, by repeated pressure
reduction. Holding and increase are repeated to maintain vehicle stability and to improve steerability during sudden braking.
VSC Operation
The vehicle could be in an extreme over steering or under steering tendency due to unexpected accidents, road conditions,
vehicle speed, or by other external factors. In such a case, this system automatically controls the engine output and the
braking to each wheel, to decrease the extreme over steering and under steering.

∗ To decrease extreme over steering tendency

When the system determines that the over steering tendency is large, the system applies brakes to the outer wheels

according to the degree of over steering, and creates a moment towards the outer side of the vehicle, to decrease the

tendency of over steering. Also, when the brakes are applied, the vehicle speed decreases while the stability increases.

∗ To decrease extreme under steering tendency

When the system determines that the under steering tendency is large, the system applies brakes to the front or rear wheels
according to the degree of under steering, to decrease the tendency of under steering.

When the VSC operated, the skid control ECU with actuator sends a signal and the slip indicator in the instrumental cluster

will flash and a buzzer will sound to warn the driver than the tire grip is at its limit.

Active Traction Control (4WD)
While driving with the 4WD mode, the active TRAC system helps control the spinning of the wheels which may occur when
accelerating on a snowy road or during severe off–road driving, by controlling the brake fluid pressure of each wheel. The
system distributes the traction lost by slipping to each wheel, which produces a strong LSD effect. When the active TRAC is
in use, the skid control ECU with actuator sends a signal and the slip Indicator in the instrumental cluster will flash to notify
the driver.

Traction Control Operation (2WD)
Estimating the vehicle speed from the rear wheel speed, comparing it with the front, driving wheel speed and judging the grip
condition of the driving wheels. From the estimated vehicle speed, target speed of the driving speed will be set. When the
front, driving wheel speed exceeds the control starting speed, it judges that the tire slip is occurred and performs the
electronic throttle control and brake control and then adjust to make the rear wheel speed become the traction control target
speed. Controlling of the traction control will be completed when the vehicle move on to the road where the driving wheels

will not have a tire slip or when the driver decelerate.

JTtundra · #2 (**permalink**) 08-08-2007, 10:25 AM

Question?

For the VSC & Traction control could it be as simple as swapping the wires somewhere in the circuit so that the default circuit is VSC & Traction control off instead of on? Where you would have to push the button to engage them both.

Don't know if it could be that simple, But figured I would put this out to the masses.

Squid · #3 (**permalink**) 08-08-2007, 10:34 AM

The first drawing of the PDF tells me that a toggle switch replacement of the traction button should give you the ability to turn it on or off at will. If I had a Tundra parked outside I'd be out there right now with my meter verifying this.

chicksdigemtoo · #4 (**permalink**) 08-08-2007, 12:19 PM

:blahblah::blahblah::blahblah:

Now again in english? lol

So....when I hit the button it turns the button it turns the traction control operation on and when I hit the button for 3 seconds it turns the traction off and the VSC off? Or does that turn the traction on and the VSC off? Inquiring minds want to know.

The issue I am having is on rough surface roads with many pot holes ( JERSEY) it seems my back tire slips and the engine breaking "breaking" thing starts happening. I feel a little out of control of the truck.

Thanks for looking into this Squid!

Skyhammer · #5 (**permalink**) 08-08-2007, 02:45 PM

Chicks, here is how it works.
When you start your Tundra, VSC and TRAC are on by default. Both of these systems regulate your throttle.
Push the button once and TRAC is turned off and A-LSD is turned on, VSC is still on also. A-LSD works like TRAC except it does not interfere with with throttle. A-LSD has speed limitations, it is something like 62mph. Toyota does not want us to use A-LSD all the time. I think(but am not 100% certain), that the reason Toyota doesn't want us to A-LSD all the time is because the speed sensors will sense that when we turn a corner, one wheel is going faster than the other and A-LSD will try to correct that, causing excessive wear on the brakes.
Holding the button for 3 seconds results in TRAC, VSC and A-LSD being turned off.So no traction control, skid control or anything else.

chicksdigemtoo · #6 (**permalink**) 08-08-2007, 03:23 PM

okie dokie... now I understand. See...your teaching abilities just paid off! I am now edumacated.

whippa · #7 (**permalink**) 08-10-2007, 04:07 PM

Gosh ...that was worth the price of admission !! Sooooooo

1. start truck
2. push button for 4seconds
3. motor on..

unless of course , you anticipate slick roads..

vukatron · #8 (**permalink**) 02-26-2008, 05:26 PM

It does turn off all these options when you hold the button down for 3 sec., but if you drive radical enough, the computer will still take over control,,, trust me.

papifun · #9 (**permalink**) 02-26-2008, 07:40 PM

question - A-LSD isn't it like auto limited slip differental ?
I disable the trac control in light snow covered roads because it will again save my rear brakes and stop the constant retarding of the motor. By just disabling the trac control but still have the LSD it allows me to spin the rear a little before the engine reacts and rear brakes. - if i spin hard then it will kick in the brakes. This also allows the VSC to still operate if i begin to fish tail. In 4x4 the VSC is Off by default, i found it better to also disable the trac control..you will begin to use a pattern best for your driving conditons depending on road conditions in your area. hopes this makes sense.

turning everything off on dry payment and just press hard on gas is also fun !!
i dont think if u drive "radical" the ECU will kick in and then trac control,VSC will happen. skyhammer great info and very clear, didnt know that at 62 miles the cutoff for LSD - makes sense but what about if u try to do a emergency manouver on a highway when driving over 70mph ? is it disabled ? will only VSC work ?

Frag Master · #10 (**permalink**) 02-27-2008, 06:05 PM

Nice job Squid, much better than the salepeople ever do. Of course the reason being they don't really understand the differences themselves.

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