I am considering buying a 2003 Subaru Outback wagon with 115k miles on it. It showed a P0420 trouble code in memory, but the check engine light was off. When I cleared the memory, the check engine light came on in about 60 miles/ 6 engine cycles and does not go out. The seller supposedly had the two O2 sensors replaced. This problem then recurred. I am told to just wait and the check engine light will eventually go out as the two O2 sensors must ''communicate with each other''. This does not seem right. What is the problem? I don't want to buy an expensive problem. Where I live I cannot register the car without it passing an emissions check which WILL check for any trouble codes.
A p0420 code is set when the computer determines that the catalytic converter isn't doing it's job. In almost all instances that code can't set as a result of a bad o2 sensor so they probably didn't have to be replaced. The catalytic converter will need to be replaced, prefferably by an oem part. This can be pretty expensive and should be considered before purchasing the vehicle.
I have replaced a few bad converters on late model subarus in the past few years.
http://engine-codes.com/p0420_subaru.htmlForum CodePossible causes- Three way catalyst converter Bank 1 1,869 views
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