Replace catalytic converter or oxygen sensor? Not sure what to do.

[Ford Man]

Originally Posted by nemesis

Check engine codes do not tell you which part is bad, they tell you what's being affected. Just for the future reference.

This may be true in some cases, but PO420 usually does indicate a bad converter. I think the the definition for the code reads something to the effect of "insufficient catalyst efficiency" meaning the 02 sensor detects a problem with the polution in the exhaust gasses. The codes are there to steer you in the right direction of things to look into. Yes, it's possible to have certain codes that will give you several things to check that may not be the fault, but could contribute to the problem. Several years ago I took a car in for emmisions testing (tail pipe sniffer test) and the readings maxed out the emmisions testing equipment (pre OBD II) and the problem was a bad vacuum line.

[Ryland]

I did some work on my girlfriends car a few months back, she also has a Toyota Corrola with the same P0420 check engine light code.
First thing I did was checked the gas cap, the seal on the gas cap was bad, 2nd thing I did was had her only run non ethanol gasoline.
3 months or about 4,000 miles later and her check engine light has not come back on, her car is still burning oil but it seems to be burning it and not damaging anything, so that would be my advice, use better gasoline and install a new gas cap as they have a check valve in them that can wear out.

[Ford Man]

Originally Posted by Ryland

2nd thing I did was had her only run non ethanol gasoline.

Some of us are not lucky enough to have a choice between straight gas or ethanol laced gas.

[blade]

hey carwhat just my two cents but fordman is giving you the best direction on fixing your problem you can also ohm test an o2 sensor but if its oil coated you need to pull it out and clean it or replace it you will need probable need a special wrench to remove it you can borrow from autozone and i believe advance auto dont through parts at it find the problem first (usually)