P420 code....

[airdreams1]

Was pretty sure I had a leaking fuel injector. So I replaced the injectors with six remanufactured ones. The check engine light came back on again for the same code. Now I'm wondering what else might be the issue. Obviously could be the oxygen sensor or catalytic converter. Is there anything else that it could possibly be?

 

[Endlessblockades]

Was pretty sure I had a leaking fuel injector. So I replaced the injectors with six remanufactured ones. The check engine light came back on again for the same code. Now I'm wondering what else might be the issue. Obviously could be the oxygen sensor or catalytic converter. Is there anything else that it could possibly be?

In my case, an exhaust leak downstream from the cat (beyond the flange, on a self-installed exhaust system) caused the P420. Worth checking your connections beyond the second 02 sensor - you might get lucky.

 

[jgue467]

Yup exhaust leak will trigger it.

On mine and some others on here, its been reported usually when off-roading traveling 5 or so mph for a couple miles or more will also trigger the 420. Mine does it like clockwork under this condition only, I can then clear the code and drive hundreds of miles city and/or highway and no 420.

I just clear it and drive an hour or so before each annual safety check and it passes. Luck.

 

[MaineRunna]

Make sure engine has the correct duel ground electrode spark plugs in good condition, a clean air filter and is running well first. Next check the exhaust system for leaks near the converter and downstream O2 sensor. I find that leaking flex pipes, worn out flanges, blown out gaskets or small holes where heat shields, hangers, etc were welded on the exhaust are the most common cause of P0420 on most vehicles. If you bang on the converter and hear something rattling around or view you engine data on a code reader and the downstream O2 sensor mimics the upstream sensor you need a converter. Could also be caused by bad O2 sensor or MAF sensor.