Scotty-. I have a 2012 f150 with a 5.0 V8. 140,000 MI. Automatic transmission. The P0420 and P0430 codes have been intermittently going off and on for the last couple years. It seems to stay on all the time in the winter when it's cold but then will sporadically go off and on in the summer months. Sometimes the codes will stay off for weeks at a time then randomly turn on for a couple weeks then shut back off. Would bad catalytic converters throw off intermittent trouble codes like that? Thanks very much
See below: there can be other causes as well, need to do the proper diagnosis. Be sure all the wiring/connections/welding are solid on the upstream/downstream O2 sensors and the catalytic converters and also no holes/leaks in exhaust system surrounding the Cats. See below for detailed troubleshooting - will need a scan tool with live data capability (preferably one that can plot the data in graphs).
(same for P0430)
https://www.yourmechanic.com/article/p0420-obd-ii-trouble-code-catalyst-system-efficiency-below-threshold-bank-1-by-jamahl-walker
https://m.youtube.com/watch?v=xLyytQD7njw
https://m.youtube.com/watch?v=CflIvd5VOoA
Check the down stream O2 sensor first. Also, look for any leak in the exhaust.
