2004 LX470 - Replaced both Cats and 4 O2 sensors - still getting P0420 (1 Viewer)

[gunit470]

Hello everyone! I have a 2004 LX470 with 219k miles currently. Bought it 15 months ago with CEL/P0420 code and debated on getting exhaust replaced. Found a guy that could get me Lexus parts (with O2 sensors) for both sids much cheaper than dealer pricing... anyway, he replaced all O2 sensors and cats on both sides. It runs great, but the P0420 keeps coming back. I reset it with my code reader, and it stays off if I'm driving it for a while, highway trips, longer continuous drives, etc. But as soon as I start driving short trips and turning it off and on the CEL comes back on.

I heard somewhere that it would take 15-20 starts/trips before it would clear itself, just can't imagine why it won't stay cleared with (mostly) all new parts.

If anyone has experience or advice I'd love to hear about it... the truck is fantastic.. my 4th LC/LX and this is my favorite.

Thanks for any help you can provide.

*note - i do have a ticking sound on startup when it's cold but that goes away when it warms up.

 

[Scrappy]

I would take it to a shop to get the exhaust system looked at and confirm there aren’t any leaks. Possible your mechanic didn’t seal everything up properly, or the problem was never the cats and o2 sensors to begin with. Read plenty of stories of these codes getting misdiagnosed as cat issues when in reality it was something else. P0420 means there’s an issue with the driver side exhaust. I had P0430 (passenger side) and found that there was a leak at the rear o2 sensor. The leak could be coming from a variety of places in your situation.

 

[GuitarsandMopars]

I recommend stuffing a rag in the tail pipe and getting under the vehicle and listening for exhaust leaks. You'll need someone to hold the rag in place (unless you have a really big exhaust leak).

 

[excessive]

The ticking sound is leaking exhaust manifolds, but that shouldnt be leaking enough to cause the codes. An engine vaccum leak or something like the may cause the codes. I would get a copy of techstream and make sure your voltages look good coming from the 02 sensors

 

[gunit470]

Thank you everyone for the ideas! I will see what I come up with this weekend!