throwing PO420 code

[almac4]

My check engine light went on and the code threw out PO420. I replaced the rear o2 sensor and still get the code. Im hoping its not cat converter. Isnt it too soon for the cat to go on a 03 with 90,000mi? way to figure out whats throwin the code?

[ShawnM]

Its the converter. Its just about always the converter with a 420 code. And no 90K miles is not too soon. Dos a search on that code, im sure youll find hundred of threads n it.

[aleksei7]

ya its the catalic converter had the same problem, changed the catylic converter 100000km on warranty and went away, also had to change the intake manifold gasket which caused the catylic converter to go bad

[mikered30]

P0420 is not always a bad cat, it could be a bad rear oxygen sensor (which you checked) or a leak. 90K miles is not that bad for needing a new cat.

[cny03owner]

There's a good bit of discussion on the P0420 code in this topic:

'03 LE - P0420 Code

Dealer will tell you to replace the cat and the sensors all at once. After hearing what others have said, you've started down the right path by starting with the one sensor.

I found that my car throws a P0420 code under a specific set of conditions -- usually interstate driving, over 1 hour in duration, at speeds of 65-70 MPH. Around town, I don't have an issue. I invested in a code reader to reset the light, and have chalked it up to a quirky sensor.

I forget what the exhaust system warranty is on the '03, but recall it may be 100k. If that's the case, you may want to talk to the dealer about the problem... you may get the cat replaced under warranty.

[MoTNguy]

Hi all. Before buy the service technicians story on the cat, check out my story and try the fix. It cost me $8.00 to "legally" turn off the P0420 induced CEL. My03 started pushing the code about a year ago. Got the same response from the techs as you. However, the light went out when I spent a week in Florida last July driving on Florida gasoline. Drove home on FL gas, no light. Fill up with Tennessee gas, CEL is on 16 miles later. It aint the cat, it's the ethanol blended gasoline. I suspect the programming genius did not take into account the possibility of the usage of ethanol blended fuel and thus the P0420. I have Honda throwing same code. I employed this fix on both vehicles and no light.
Go to this link: http://www.honda-tech.com/showthread.php?t=2162522. Follow it exactly and you have a good chance of ridding yourself of the P0420 CEL and saving yourself enough money to go for a nice vacation.