srgilbert

Hi,

I really can use some advice here. I continue to get a P0420 code weak bank 1 cat on my 95LS400. I've replaced the front oxygen sensors with Densos and the problem did not go away. I took the car on a 300 mile trip last week after the reset and the light came back on after 250 miles. I reset the ECM and I managed to get another 300 miles antil I hit town driving and it came back on. Today I plan to flip the rear sensors to see if the code goes to P0430 which will point to the other cat however I doubt this will happen. I checked with Lexus and the cat is roughly $900 which is not an option. I'm finding that used ones do not seem to be available through junk yards due to EPA ....

Any thoughts? ANyone with the same experience?

THANKS!

Byrdman

Sounds like exactly how i would have described what happened with my '95 a couple of months back. Had a friend test the sensors and we ended up replacing one, still kept throwing the same code you have some 200-300 miles after resetting. Ended up looking at the exhaust pre-cat pretty close and looks like a gasket was shot. $20 dollars later with Midas throwing in some muffler mud, code has been gone for over a 1,000 miles now.

good luck

srgilbert

Thanks for the response. I believe the problem started when the seal began leaking 6 months ago. The dealership sealed it up however this amy have caused some longer term problems. The last 2 times the check engine light went on the P0136 code was stored and no P0420. Getting to the rear oxygen sensors appears to be a bit painful to test.

When Midas resealed this for you was there an obvious noise for escaping exhaust?

Thanks again

Byrdman

The leak wasn't real obvious. When it threw the code, the mechanic found one sensor that wasn't reading at all, of course it wasn't the bank indicated by the code & thought one on the side rear was reacting slow. A couple of 100 miles later, tripped it again. I was going to go ahead & just replace the drivers front as as the next step even the the mechanic said it tested fine. When i climbed under to see what all was involved, could just hear small leak while i was underneath and could feel some air movement. Figured had nothing to lose by a trip to Midas. I'm sure the lexas gasket was special order so easier to see if their "muffler mud" solved it. Going on 3 months now. Good luck in tracking yours down.