Need help with P0420 code

[Matrix_Jim]

Been getting the P0420 code so I replaced the rear O2 sensor and disconnected battery for 10 minutes. Light came back on after a couple of days so I replaced the front O2 sensor. Light came on after about 20 seconds this time. The front sensor was a Bosch 15730 universal replacement and is wired per directions. Could this sensor be incompatible with my 2003 front wheel drive base model? Inspection is due in 11 days so I am running out of time. Anyone ever experience this? I also ran seafoam thru my brake booster line and added the other half to my gas. Car is running great just that light is driving me nuts. Appreciate any advice anyone may have. Thanks

[PA Firefighter]

Spotted this over on MatrixOwners.com

http://matrixowners.com/index.php/to...135-and-p0420/

Sounds like a similar issue, and the solution might be in there for you.

I got that same code about 6 weeks ago, and bought some Lucas Fuel Treatment and the check engine light went away in less then a week. Might sound silly (and you probably checked already) but is the gas cap closed all the way? That has been known to throw a P0420...

Hope it helped!

[sam333]

Toyota's dont like bosch 02 sensors and dont run seafoam ( fouls 02 sensors and cat).

[Matrix_Jim]

OK so I replaced the downstream sensor before the seafoam and upstream after the seafoam. Does that mean neither Bosch sensor will work?