Code P0420 Returns

From '96 Ford factory OBD-II manual, possible causes for DTC P0420:

Use of leaded fuel Oil contamination Cylinder misfiring Damgaged HO2S sensor Damaged ECT sensor Downstream HO2S wires improperly connected Fuel pressure too high Damaged exhaust system pipe Damaged exhaust manifold Damaged muffler/tailpipe assembly Damaged/Bad Catalytic Converter.

Don't forget, the downstream O2 sensors monitor catalyst efficiency only, if the system finds that the catalyst system is greater than the emission threshold a code will be set.

Thanks Fred for excellent reply.

Took it to dealer (not original mechanic who did injector cleaning) who reported that the catalytic converter was indeed bad. It's been ordered. Lucky for me, my Explorer has under 80K miles and is under 8 years old, so it's all covered under warranty including diagnostic. Otherwise it would have been an expensive repair. Parts alone are over $600.

ADVICE FOR ANYONE WHO MAY BE HAVING SIMILAR PROBLEMS: Don't delay seeing the dealer if you're approaching 80K miles or 8 years.

Now your question should be, WHY did my catalytic converter go bad? My understanding is that catalytic converter's don't just go bad, that is, there is something that contributes to their failure and unless the real culprit is addressed the same thing will happen again given time...

Steven

Len Krauss wrote:

I've seen several go bad, just because we live in an imperfect world. They just 'curl up and die', so to speak. The innards sometimes come loose, compact themselves, and the exhaust no longer gets treated. It happens.

I should have been more specific with regards to previous failures that had been corrected, however, in that case the question would/could be answered. Though your reasons for failure... I don't know... I wouldn't buy them/it??

Good luck,

Steven

Are you saying they don't do this? They have done it. Usually after an overheating problem from getting too much raw fuel into the cat.

My wife triggered this by putting in a full tank of 93 octane. I ran it down to empty before the next fill ups. I reset the codes after about each

I read somewhere that the computer learns what is normal and a big change in octane will make it think things have failed.

check-engine