RocketMan295

Perhaps my DIY experience will help other 5th generation ES 350 owners. My 2009 (101K miles) developed a very audible exhaust leak, worsening over a week or two. Checked a schematic, learned there’s three cats, one flex joint in addition to mufflers and resonators. Mucho dinero for certain, decided to pressure test entire system for accurate troubleshooting. (Will explain my leak testing should anyone request the details) Long story short: couldn’t locate any leak. Had a hunch it could be the exhaust manifold/converter-to-head gaskets. Removed all exhaust components to the workbench, examined closely, no cracks or rust throughs. Turns out the factory manifold-to-head gaskets were simply 2 sheet metal laminations (.020 total thickness), no fibrous material whatsoever. I bought a FelPro gasket set; much thicker with a faux asbestos core, very compressible. (The type of gaskets I grew up with!) Sequentially torqued to 15 foot-pounds 180 inch pounds. Reassembled with ALL the old parts. Purrs like a kitten, cost me $35 total. At age 72, all those years of experience are finally producing good results!

rx300mm

My 2007 ES350. with 150k miles, is showing P0420 error code. ECM detected error use Catalyst system cleaner.
Reading the error code on internet some people are pointing to small exhaust leak. I hope its nothing big like replacing the Catalyst system.

ESh

Put the spacers on the O2 behind the catalytic converters.

RocketMan295

I had no codes whatsoever, but the exhaust leak was loud enough to be embarrassing. As I mentioned, my leak was the original (firewall side) exhaust manifold gasket, 2 two thin layers of sheet metal total .020” thick. I did not replace any O2 sensors. Assuming (hoping!) that you are a DIY guy, my experience of removing all the exhaust components to the workbench and examining closely under sunlight resulted in a cost effective, though labor intensive, repair. Replacing catalytic converters (that are designed to last the life of the car) and other exhaust components can easily exceed the value of the car. Best of luck, friend!