1993 LS400 97,000 miles. Check engine light flashed on twice on highway for a few seconds on two seperate days and once on cold start stayed on 5 minutes. No noticable effect on performance. Did code check and found code 25 (Air Fuel Ratio Lean Malfunction). Did suggested code 25 diagnostic tests in service manual for "open or short in main oxygen sensor" and "open or short in injector circuit, injector leak, etc" (page EG-569, 570). Both detected failures. Did other suggested code 25 tests on page EG-572 for O2 sensor signals. Found OX2 (0.5 volt maximum) going to about half of OX1 (1 volt maximum) and VF2 seemed to be fluctuating more sporadicaly than VF1.

Not sure if it matters but this LS is originally from California.

Does this sound like a bad #2 main oxygen sensor ?? If so any tricks to replacing ?

Thanks - Herm

 

Herm,
Do a visual check on the injectors and try to smell for fuel in the engine bay. If you do not see any wetness or smell any fuel it's most probably your main O2 sensors. If you don't want to cut the wire from the old sensor to fit a socket, buy a special O2 socket ( has open side to fit wire through ). If it's stuck, spray some rust penetrant, other then that nothing too hard.

Regards

 

your front o2 sensors need to be changed. get a universal and splice the wires, save 100 bucks in the process.. it'll take about 2 hours total to do the whole thing and figuring it out

 

Thanks VVT-i, Nick T, and persian451. The main right 02 sensor was bad (low voltage output) and replacing it cured the problem. Old sensor was black with soot which I presume is because computer thought mixture was too rich, even thought it was not (due to bad O2 sensor - I hope ! ). Very interesting that a failed O2 sensor code did not come up. In doing the job I FOUND WHAT I THINK IS AN ERROR IN THE LEXUS SERVICE MANUAL , which caused me to initially replace the wrong sensor and get very discouraged when the problem reappeared! Page EG406 (figure po1333) indicates the underhood diagnostic connector (DLC1) pin OX1 monitors the right bank and pin OX2 monitors the left back. I found the opposite to be true. The information on page EG558 of the manual agrees with my finding. Has anyone else run into this ? Is there a list of corrections available for the manual? THANKS - Herm

 

you might as well change the left side as well, because that will prbably go bad eventually, save yourself the time