lexie

My '91 LS TRAC light turn on and stay on when I drive the car for few minutes. But the light goes off right after I restart the car and it turn back on after driving for another few minutes. Any idea of what causing the light to stay on
Could that cause by the oxygen sensor?

JTJerryls400

I saw that in one lex when I want buy lex. Of course I do not buy it (that light was reason) but owner when it light was doing something in traction control box (under the hood) and after that light went off.
Jerry

chliansh

Mine does the same thing (94 LS400)

From what I have read I think one of the O2 sensor is getting lazy.

I have noticed when you start it for the first time in the day and drive a short distance (less than a mile) and stop it comes on. I first get the check engine light which then disables the traction control system and triggers another light.

I believe the O2 sensors in our cars have a heating element inside to quickly bring it up to operating temp and I think that part is failing. Once you run the car for awhile the exhaust provides all the heat it needs to function

Try and rev the engine to 2500rpms for 30 secs or so before you drive. It seems to be just enough to heat things up and solve/hide the problem.

Chad

wwest

I'm assuming Trac light alone and not with engine check light.

Check all four wheel speed sensors for tight connections and no frayed wires.

epineffreen

in my 90 LS, it does the same thing, but my antilock light illuminates also... what's goin on herE?

chliansh

I really think its just a bad\lazy O2 sensor slightly out of spec.

1. ECU gets an out of spec signal from one of the 02 sensors which triggers the "check engine" light

2. Check engine signal tells the ECU somethings wrong, go into default\closed loop mode. This is when the ECU ignores all of the feedback from the various sensors and uses the pre prog. values
to control engine management

3. Traction control will not function properly when the ECU is in closed loop mode because the feedback it needs is not there so by default it turns it off and throws the "traction control" light.


I just bought my 94 ls 400 3 weeks ago. The second day I had it this happened to me so I searched all of the archives and this is what I came up with. Seems like it might even be an evil trick by our friends at Toyota to throw off Joe Blow the local mechanic and get you back to the Lexus service center? I found a couple of threads were techs miss diag. the traction control light problem
and replace the traction control unit at around $1500 only to find out is was a $100 o2 sensor

rybikowsky

my 92 ls 400 was doing the same thing.I took it to my tech.And he reset the computer,if thats what its called,and it has been fine ever since.

JTJerryls400

Check engine signal tells the ECU somethings wrong, go into default\closed loop mode. This is when the ECU ignores all of the feedback from the various sensors and uses the pre prog. values
to control engine management

IT IS WRONG. CLOSE LOOP OPERATION IS NAME "CLOSE LOOP" BECAUSE ECU HAVE FEEDBACK FROM SENSORS. WHEN NOT, IT IS OPEN LOOP MODE, SO WHEN 02 SENSORS ARE COLD OR HAS MALFUNCTION WHEN ECU IS IN OPEN LOOP NOT CLOESE LOOP. CLOOSE LOOP MEAN THAT ALL SENSORS NEEDED FOR FEEDBACK ARE WORKING AND WORKING IN OPRATION RANGE.
JUST MY 0.02$

Jerry

healerhand

Well,

I have the same problem with my TRAC LIGHT. I just got two new front O2 sensor from the dealer. I will let you know if the TRAC Light goes off or not.

david

wwest

One of us is.

If the trac light is on but not the engine check light why are you replacing the oxygen sensor?

chliansh

For some reason the "traction control" light seems to show up WITH the check engine light. Thats why I tried to explain whats going on with all of the signals and lights in my earlier posts.

In summary I think the traction system is auto disabled
by the ecu when it notices a bad signal from the O sensor. I assume they designed it this way because they thought the traction control system had a good chance of malfunctioning if the engine was not running 100% perfect (check engine light). So to be safe they shut off traction control as soon as the error is detected.

I think the confusion comes in because everyone assumes the worst (mechanics included)when they see the traction control system deactivated.


Closed loop open loop... My understanding was the ecm "default mode" was called closed loop because it was no longer using all of the sensor info to control engine management. for example in open loop "regular mode" the ecu is constanly adj air fuel mixture
based on the values it gets from O2 sensors.

Open loop: ecu is constantly making changes to many of the engine systems based on info from all sensors (coolant temp, air temp, oil pressure, o2 sensors ect)

Closed loop: Ecu is closed off from -most- sensors and is no longer
adjusting engine based on sensor info and instead is using default values to keep things working until repairs can be made. Engine still runs but not perfect. Poor gas mileage is something commonly noticed if you run for awhile with the check engine light on even if you have no major problems.

chliansh

rybikowsky

Has a pretty good idea with ecu reset. This could vary well work in some cases because when the ecu goes through its relearn process it might be able to learn around small problems.

healerhand

Well,

I got two new front O2 sensor replaced last night. It DID NOT work. The TRAC light still comes one. Perhaps i will used the old O2 sensor and replace it with the rear O2 sensor. I will let you know by Thursday night.


david

lexie

For some unknown reason, my TRAC light doesn't stay on any more. Back to normal. Really strange

Healerhand: any luck with the rear O2 sensor?

healerhand

i am doing it today.