Tell me about the SC's traction control system
12-05-05, 10:27 AM
#16
manual(5sdp) = you have full control
auto w/ traction = traction control the wheels
auto w/ traction = traction control the wheels
Originally Posted by djeffers
I have a 96 Lexus SC300 5spd and my previous cars were a 91 nissan 300zx 2+2 and a 87 mazda rx7 turbo2. I've never driven a car with traction control so I can't tell too much. I heard it was an option (which my car probably has w/heated seats, etc). Cut to the chase - How do I know if my car has traction control - how do I disengage it? 
12-05-05, 11:04 AM
#17
Zombie Slayer
Originally Posted by jpvarghese
There should be a button by your fuel/trunk switch for traction control. Also if your wheel start to slip you will feel the engine bog so the tires on all four corners rotate at the same speed. hope this helps
Does yours have a switch by the trunk release?? To the best of my knowledge the trac on/off button was only located by the shift lever. Also, the trac control does not equalize the speed of all 4 wheels. Especially since only 2 wheels are even powered! The trac control unit is simply an additional butterfly inside the intake manifold that closes when there is spinning of the rear wheels. The closing action of the butterfly decreases the amount of air being taken in, effectively decreasing the amount of power the engine produces. If you really want to confirm that your car does or does not have traction control. Open your hood. If you see a black cover that says TRAC behind the intake, you have it. If you don't see it, you don't have it. Simple.
12-13-05, 09:23 AM
#18
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No TRAC, please
I have driven lots of rear wheel drive cars through snow in my life, but the SC is one of the worst at it. I like to slide a little cuz its fun but once that back end swings out in a turn, its hard to reel it back in smoothly. Usually it just keeps going until you do a 180. I like to have the rear loose so I can have fun but this thing has no control.
Anyway, the traction control came only on AUTO 300's and 400's. It is 15 year old technology and even when new it was nothing special. To "control" the traction the ecu recognizes when a wheel is slipping by comparing the speeds of the wheels. When a rear wheel starts to turn faster than the rest, 2 things happen. The brakes are applied to that wheel and the throttle is limited until the wheels turn at the same speed while the TRAC light flashes in the middle of the tach. Meaning, no matter how hard you push on the gas it will be cut back at the throttle by the ecu.
This sucks when you are trying to accelerate out of a turn and the throttle keeps getting overridden due to wheel slip, which is fun.
The traction control is a useless option and I turn mine off always, even in the snow. A torsen, or limit-slip differential would be much more effective than the TRAC system at controlling traction.
Anyway, the traction control came only on AUTO 300's and 400's. It is 15 year old technology and even when new it was nothing special. To "control" the traction the ecu recognizes when a wheel is slipping by comparing the speeds of the wheels. When a rear wheel starts to turn faster than the rest, 2 things happen. The brakes are applied to that wheel and the throttle is limited until the wheels turn at the same speed while the TRAC light flashes in the middle of the tach. Meaning, no matter how hard you push on the gas it will be cut back at the throttle by the ecu.
This sucks when you are trying to accelerate out of a turn and the throttle keeps getting overridden due to wheel slip, which is fun.
The traction control is a useless option and I turn mine off always, even in the snow. A torsen, or limit-slip differential would be much more effective than the TRAC system at controlling traction.
12-13-05, 09:40 AM
#19
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Mine says "TRAC/ PWR" but there are actually 3 settings. When you first start the car its normal. When you select PWR it chsnges the shift points in the tranny for better acceleration.
When you select "SNOW" it decreases power output regardless of wheel spin. Its kind of a way of Detuning the motor. I also found its a good way of increasing gas milage for those of us with heavy feet.
When you select "SNOW" it decreases power output regardless of wheel spin. Its kind of a way of Detuning the motor. I also found its a good way of increasing gas milage for those of us with heavy feet.
12-13-05, 09:57 AM
#20
Zombie Slayer
Originally Posted by Project300
To "control" the traction the ecu recognizes when a wheel is slipping by comparing the speeds of the wheels. When a rear wheel starts to turn faster than the rest, 2 things happen. The brakes are applied to that wheel and the throttle is limited until the wheels turn at the same speed while the TRAC light flashes in the middle of the tach. Meaning, no matter how hard you push on the gas it will be cut back at the throttle by the ecu.
The traction control system simply and only limits the amount of air entering the engine, reducing power output and limiting the car ability to spin the wheels.
Not trying to ruffle feathers, just trying to keep misinformation from populating CL.
12-13-05, 12:32 PM
#21
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Some constructive disagreement posting is always welcome with me. Especially if it is to keep the info clear.
But yes, the car can and does apply brakes to each wheel individully as part of the TRAC traction control system. It's basically using the ABS system to do this, which is designed to operate the brakes for each wheel independantly. You can hear the TRAC system applying brakes when the TRAC light is blinking and it sounds similar to when the ABS is clicking. Check under your hood and look near the fire wall on the passenger side of any SC. See all those curly brake lines? Thats the ABS system and you'll notice there are 4 hydraulic lines, one for each wheel. These operate separate from the normal braking system and are used by the TRAC system too.
Think what would happen if the system only reduced the power: Since our cars dont have a limit-slip diff (LSD), the wheel with the least traction would still receive the power (just less) and still spin. But by applying the brakes individualy with TRAC to one wheel it actually sends some power thru the differential to the other wheel that is not spinning. This is the key feature of the system. You just trade power for traction with the TRAC system.
Volley.
But yes, the car can and does apply brakes to each wheel individully as part of the TRAC traction control system. It's basically using the ABS system to do this, which is designed to operate the brakes for each wheel independantly. You can hear the TRAC system applying brakes when the TRAC light is blinking and it sounds similar to when the ABS is clicking. Check under your hood and look near the fire wall on the passenger side of any SC. See all those curly brake lines? Thats the ABS system and you'll notice there are 4 hydraulic lines, one for each wheel. These operate separate from the normal braking system and are used by the TRAC system too.
Think what would happen if the system only reduced the power: Since our cars dont have a limit-slip diff (LSD), the wheel with the least traction would still receive the power (just less) and still spin. But by applying the brakes individualy with TRAC to one wheel it actually sends some power thru the differential to the other wheel that is not spinning. This is the key feature of the system. You just trade power for traction with the TRAC system.
Volley.
12-13-05, 12:45 PM
#22
Zombie Slayer
Touche!
Project300 +1
mkorsu 0
I guess I stand corrected. Your explaination makes perfect, logical sense. And since my response was based solely on assumption, I must defer to your conclusion.
But, a question. If in fact the system brakes the spinning wheel individually, why even bother with decreasing power?
Project300 +1
mkorsu 0
I guess I stand corrected. Your explaination makes perfect, logical sense. And since my response was based solely on assumption, I must defer to your conclusion.
But, a question. If in fact the system brakes the spinning wheel individually, why even bother with decreasing power?
12-13-05, 01:11 PM
#23
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Originally Posted by mkorsu
But, a question. If in fact the system brakes the spinning wheel individually, why even bother with decreasing power?
One possible answer is that the brakes and differential have to absorb power to "create" traction. This could be a problem if you floored it (a long time) and sent power where the brakes are trying to limit it. TRAC gives the ECU control of the 2 main things used to control traction: power and braking. You really need both for the system be effective.
It also makes sense in theory. If you have a spinning wheel, a lame way to get it under control is to take some power away.
It could all be replaced with a LSD, IMO.
12-13-05, 01:25 PM
#24
Zombie Slayer
Originally Posted by Project300
Good question! Thats my main problem with the TRAC. Dont mess with my throttle!
One possible answer is that the brakes and differential have to absorb power to "create" traction. This could be a problem if you floored it (a long time) and sent power where the brakes are trying to limit it. TRAC gives the ECU control of the 2 main things used to control traction: power and braking. You really need both for the system be effective.
It also makes sense in theory. If you have a spinning wheel, a lame way to get it under control is to take some power away.
It could all be replaced with a LSD, IMO.
One possible answer is that the brakes and differential have to absorb power to "create" traction. This could be a problem if you floored it (a long time) and sent power where the brakes are trying to limit it. TRAC gives the ECU control of the 2 main things used to control traction: power and braking. You really need both for the system be effective.
It also makes sense in theory. If you have a spinning wheel, a lame way to get it under control is to take some power away.
It could all be replaced with a LSD, IMO.
I agree with the LSD answer...........partially.
Yes, I feel it would aid traction in a straight line since as one wheel began to slip, power would be diverted to the wheel with more traction. But, since we know what driving with a LSD is like, when making a turn or if both wheel slip while traveling straight......................WHOAH!!! Super Slide!!! A better driver can make it work, unfortunately too many "tuners", if you will, want to put them on their cars and think it solves all traction issues and that the car can be driven exactly as before. Doesn't work that way.
Ok, I 've gone way OT!!
Sorry.
12-13-05, 02:01 PM
#25
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Originally Posted by mkorsu
I agree with the LSD answer...........partially.
A better driver can make it work,.....
A better driver can make it work,.....
Check out this page:
http://www.houseofthud.com/differentials.htm
It has a ton of clearly explained info on all types of differentials and traction control systems. Scroll down about 2/3 of the page and check out "EDL (often referred to as traction control)". This explains how the TRAC system works. I couldn't agree more with the author's opinion of EDL, and it ain't good.
Happy sliding and reading.
12-24-05, 08:05 AM
#29
The Lexus Traction control on the SC's at least up until 97 does not apply the brakes to control traction. All the brakes lines are for the ABS, not traction control,
This is according to the Lexus service books, in both the Trac control, and braking sections of the manual.
Trac section only talks about the control unit under the hood driving the first Throttle body, and the braking section has no discussion about applying rear, or any brakes for traction.
Now newer Trac systems do this, but not on the early SC's
Traction control is simply an additional throttle body which closes when the computer senses tire spin.
And this system works better for forward motion then an LSD.
I've installed a supra LSD on my SC, and tire spin now causes the rear to swing sideways, not help the car move forward.
Although the system is sensitive for a sporty drive, it works well for the drivers who just want to move forward.
On a second note this system with boost works AWESOME. Especially in the rain.
Boost allows just enough air to get past the Trac Throttle Body to make the car very fast in the rain. Almost as fast as dry pavement.
Someone also asked about the Trac light coming on when the check engine light was on.
When the check engine light comes on the ECU turns off the Traction control.
Fix the check engine light, and the Trac should work again.
This is according to the Lexus service books, in both the Trac control, and braking sections of the manual.
Trac section only talks about the control unit under the hood driving the first Throttle body, and the braking section has no discussion about applying rear, or any brakes for traction.
Now newer Trac systems do this, but not on the early SC's
Traction control is simply an additional throttle body which closes when the computer senses tire spin.
And this system works better for forward motion then an LSD.
I've installed a supra LSD on my SC, and tire spin now causes the rear to swing sideways, not help the car move forward.
Although the system is sensitive for a sporty drive, it works well for the drivers who just want to move forward.
On a second note this system with boost works AWESOME. Especially in the rain.
Boost allows just enough air to get past the Trac Throttle Body to make the car very fast in the rain. Almost as fast as dry pavement.
Someone also asked about the Trac light coming on when the check engine light was on.
When the check engine light comes on the ECU turns off the Traction control.
Fix the check engine light, and the Trac should work again.
12-24-05, 02:54 PM
#30
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From the Lexus press release regarding the SC 300/400 models:
Which can be found here:
http://www.lexus.com/about/press_rel...e_09_01_f.html
And this link I mentioned earlier in the thread:
http://www.houseofthud.com/differentials.htm
Please read these links and explain how there is no braking involved in the TRAC system. Looks like maybe your manual is not complete?
Like I said earlier, braking control is the key element that makes the system work. Without braking, it wouldn't do anything to get you more traction. When the TRAC system limits power it is just to reign in the human tendancy to floor it when your car does not move, not improve traction. It's the brakes put the power where it is needed by taking it away from the spinning wheel and directing it to the non-spinning wheel thru the open diff.
If you understand how an open diff applies power it all makes sense.
Heated seats rule!
The optional Lexus TRAC electronic traction control system uses both throttle and brake intervention to help control rear wheelspin, and the system comes packaged with heated front seats
http://www.lexus.com/about/press_rel...e_09_01_f.html
And this link I mentioned earlier in the thread:
http://www.houseofthud.com/differentials.htm
Please read these links and explain how there is no braking involved in the TRAC system. Looks like maybe your manual is not complete?
Like I said earlier, braking control is the key element that makes the system work. Without braking, it wouldn't do anything to get you more traction. When the TRAC system limits power it is just to reign in the human tendancy to floor it when your car does not move, not improve traction. It's the brakes put the power where it is needed by taking it away from the spinning wheel and directing it to the non-spinning wheel thru the open diff.
If you understand how an open diff applies power it all makes sense.
Heated seats rule!
Last edited by Project300; 12-30-05 at 09:28 AM.