P0420 Catalyst below threshold bank 1
#16
03-21-2016, 05:04 PM
WOW!!!! I sure hope you don't ever encounter a small crack in your plastic intake manifold - or a sticky fuel injector that decides to 'occasionally' stick closed, and then 'occasionally' decide to stick partially open or close too slowly, or a mass air flow sensor that's temperature sensitive and don't work right only in cold temperature ---- or about a thousand other off the wall failures. You'll go broke replacing O2 Sensors and CATS because they have their own respective codes for lean / rich and catalyst efficiency low.
#17
08-02-2017, 04:06 PM
#18
08-10-2017, 06:36 PM
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A P420 code is telling you to replace the cat soon. VERY soon. I bought my truck (used), and within 8 months I had to take the truck in to have it fixed. Long story short, the cat was plugged and needed replacement. AND to top it all off, in California you HAVE to buy factory, because no aftermarket cats are CARB approved.
#19
08-10-2017, 09:04 PM
Hotshot
Not at all. The DTC means the cat isn't working, that's it. It does NOT mean in any way that that cat is or will be plugged.
#20
05-13-2019, 08:07 AM
Tuned
On my 2004 5.4 with 130k, code P0420 bank 1 went away after I fixed the exhaust leak that was downstream from the catalytic converter and downstream from the y-pipe at the factory clamp. I also had, and still have, slight exhaust leak at the exhaust manifold on passenger side like most 5.4's have (warped flange?). Seems odd the code went away after fixing exhaust pipe leak, but maybe it was due to restoring back-pressure? Any other theories as to why this worked? Anyway, thought I'd post this in case it helps anyone.
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