gsshopper

I can see how the TC on our cars might work well with an open differential, but in my case, I replaced my stock rear end with a Torsen unit. I don't know whether that is the cause, but frequently, when I turn right from a standing stop, the TC kicks in, and it takes several seconds for the circuit to give the throttle back - makes it hairy sometimes if traffic is approaching rapidly from the rear. The kicker is that this is happening with TC *turned off* (in PWR setting).

Does anyone know how to turn TC off completely?

AME_VIP

iTrader: (2)

exactly. Is there a fuse I can pull? I hate having to press the trac off everytime you turn the car off.

rdm20fan

go under the hood and disconect the Traction controls throttle cable, or unplug the harness to the control unit.

Project300

On my car, I never have any problem completely and totally disabling the TRAC system by simply pressing the TRAC OFF button each time I start the car. But, if you are still having the system engage even after turning it off , then you could physically disable both parts of the system; throttle-limiting and brake-control.

I would be careful here. If you only disconnect the throttle-limiting cable the brakes will still engage. This will send unchecked power to the rear wheels where the brakes are grabbing the slipping wheel.

There are 3 cables attached to the throttle if you have the TRAC system. One each for the gas pedal, the cruise control, and the TRAC system. The TRAC cable only limits the amout that the throttle can be opened, it does not operate independantly of the throttle like a choke as was stated earlier in the thread.

As gsshopper found out, the TRAC system is not at all compatible with an LSD. The TRAC will actually wear the clutches inside an LSD, so it is important to always turn it off or permanently disable it if you have an LSD.

With an LSD you will need to modulate the gas yourself to aviod wheel spin. If you can.

gsshopper

In case there's anyone else out there who (like me) didn't read the whole thread carefully - or the relevant section of my owner's manual, I finally realized yesterday that the switch that disables traction control is *not* the ECT control switch on the console. There is a separate traction control switch located by the trunk and fuel filler releases at the bottom of the dash on the driver's side, as jpvarghese stated early in this thread.



I haven't yet tested whether setting this switch fixes the cornering problem I've encountered, but even if it does, if I have to turn the traction control system off every time I start the car, I'll continue to look for a way to disable it permanently.

AME_VIP

iTrader: (2)

Interesting. My TRAC OFF is to the right and above the shifter on the center console.

It turns off when I press the TRAC OFF. Every time I turn the car on , it comes off again. I want to disable it so I don't have to press TRAC OFF every time I start the car.

gsshopper

TurboTeg, it sounds like there might be model year differences at work, here. My 99 SC4 has separate switches for Trac and ECT, as described, although I'm not sure why...

np20412

We have separate switches for TRAC and ECT too on our earlier years, its just the location of each button that is different on the model years. The 1999 you have has the Trac control button by the trunk/hood/fuel door release, while our earlier years have the button to the top right of the shifter.

Turboteg, you should look into permanently disabling it in that case, do you never keep it on, even in rain? I always disable mine also, even in the rain. I dislike this system a lot, but I do need to keep it enabled for when people other than me drive my car, just to be safe. I don't really mind pushing that button everytime I start the car, it's become a habit for me LOL.

rdm20fan

The TC controlling the brakes is on the newer models, as projects300's link explains. (sept 99) I'm sure this press release was designed to sell the 1999 model year, and not the 93.
But as I previously stated
On the early SC's the traction control unit only closes the butterfly in the throttle body. what it does on the later models, or Projects300's SC300, I don't know.
But the $300 Lexus service manual made by lexus for the lexus service techs which discuses the 92-93 Lexus SC400 only, explains it a little more clearly then the sept 99 press release.

I have diconnected the cable on my 93 SC400 for dyno runs, and I promise you the TC unit never tried to apply the rear brakes.

The new lexus models do use braking to control traction, understeer, and oversteer.
But on a 93 SC400 they do not. You can unplug the harness which controlls the TC unit under the hood (This will cause the "TRAC" light to stay light on the dash)
Or you can disconnect the cable. This will cause the "TRAC" light to come on when the computer tries to use the TC and then sees it isn't working correctly. I think it resets every time the car is started, but I may be wrong about the light reseting.

Project300

I have a 93 SC300 and the traction control system uses the brakes and the throttle, as do all years of all SC's. Traction Control without braking is just Throttle Control.

Understeer (the lateral sliding of the front wheels in a turn) is not controlled by the TRAC in any way. Oversteer (the lateral sliding of the rear wheels in a turn) is only slightly hindered by TRAC. There are advanced Stability Control systems that can help control understeer and oversteer, but the SC's were never made with that system.

AME_VIP

iTrader: (2)

thanks guys. Yes I want to permanently disable TRAC. I will unplug the harness.

rdm20fan

Glad I could help TurboTeg.

Make sure to post on here what the rear brakes do.
Lexus forgot to install the rear brake part of my "Throttle Control"
I think I'll bring it back to them.

Project300

LOL! Yer alright rdm20fan.

joel(PA)

does the traction control also cut fuel (since it is cutting air closing the throttle body?) i am running an aftermarket throttle body, and i get huge surges when the boost comes on. almost like its hitting fuel cut.

Project300

The traction control does not cut the fuel supply to the engine, but it does close the throttle which will send less fuel and air into the engine.