P0420 code cured

[ryszardsh]

I have a 98 and have been chasing a very intemittent P0420 cat efficiency code for months. Background is new O2 sensors last fall, along with new valve cover gasket, new air pump hose (broken while installing) new cam sensor.

Since December, every once in a while I would get a cat efficiency code and the CEL comes on. Car still runs well and gets good mileage. Never got any data into the data storage in the computer when the code would show up. Ran for a while with an OBD monitor plugged in and recording and even tho code/CEL came on during test, no obvious anything in data as to why. If I drove around in 3rd gear (car is an automatic) no code would pop and CEL did not illuminate. Really beginning to think some $ for a new cat would be needed.

Found a thread here that suggested the engine temp sensor might be the culprit. Have no clue why that was suggested but it has cured my bogus P0420 cat efficiency code. Several days running now, no problems/no codes/no CEL. Anyone got any clue why/how an engine temp sensor (the 4 wire unit in the block itself) could/would cause this kind of a problem? I pulled the old sensor apart after removal, did not see anything obviously amiss. Happy but still cannot figure this out.

RAS

PS, new sensor has not changed where car temp gauge reads and as far as I can tell has not changed the reported engine temps on the system, pretty consistent 98-99C on the water temp b/4 and after change. I have not run the temp test for long since the change and intend to run a 30 minute record temps with the OBD unit plugged in and recording, not that I expect any surprises.