msad1962

Have a 1991 LS400 with 67000 miles. Trac off and Check Engine lights come on. What does this mean????

Amskeptic

Start by reading the codes. If you get a 25 / 26 code off the check engine light, replace your oxygen sensors and the Trac Off light often will magically go out never to bother you again.
Colin

Do you really only have 67,000 miles? That makes two of us)

YODAONE

Do you know if timing belt has ever been changed?

If not, pull one of the cam pulley covers to visually inspect timing belt...

Have seen several LS400 timing belts with age related cracking...

msad1962

The timing belt and water pump have been replaced. Where do I get a code reader? And yes only 67000 miles from brand new in 1991. Have replaced two of the four oxygen sensors--the easy ones.

Moarpower

you dont need a code reader.

http://www.lexls.com/tutorials/intro/codereading.html

Amskeptic

Then we need to start with Last Thing Done To Engine. Were these sensors "upstream" or "downstream" of the catalytic converters? Did you have to splice or did the new sensors come as plug n play? If there was splicing involved, you will want to check the work performed, and do not overlook the possibility that new sensors can go bad.

The codes I grabbed out of my memory banks IIRC were for upstream sensors.
Colin

msad1962

Turned out to be the gas cap needed replacement. Once done the lights went out.

Amskeptic

I would never have gotten there. Thanks for following through.
Colin