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Dodge Repair/Code 0420 even after cat converter changes

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Question
I HAVE A 1999 DODGE 1500 4X4 5.9. MY CHECK ENGINE LIGHT THREW A CAT 420 BANK 1 CODE SO, I GOT A NEW CADILLETIC CONVERTER. LIGHT CAME BACK ON, SAME CODE. HAD IT CLEARED AGAIN. HAD TO SIT IN TRAFFIC @ STANDSTILL FOR ABOUT 12 MIN & LIGHT CAME ON AGAIN. SUGGESTIONS?

Answer
Hi Joy,
The code can also occur due several other reasons besides the converter:
The mechanical condition of the engine on that right bank of cylinders(excessive smoke from oil/coolant)
If the rear oxygen sensor was replaced when the cat. converter was changed, but the front sensor is still the old one, if that front sensor is 'aged' then that too can cause the code. So consider replacing the front oxygen sensor on the right exhaust manifold
Finally, check for an exhaust leak between the manifold and the converter and between the converter and the rear oxygen sensor, correcting any that you find.
I don't know which of these specifically applies but inspect for those possibilities.
Please 'rate/nominate' my answer/me (see the PS below).
Thanks,
Roland  

Dodge Repair

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Roland Finston

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Get a Free Fast answer to your repair question about a Chrysler/Dodge/Plymouth car, minivan, SUV, or truck. Problems with electronically controlled engines and transmissions as well as body wiring problems are my specialty. This free troubleshoot advice forum helps you diagnose faults, minimize repair costs or do-it-yourself.

I answer questions seven days a week and respond to you in about 30 minutes. "Maxed Out" means I am answering another question or asleep overnight so try again later.

I have do-it-yourself experience (50+ years) and a library of 100 1982-2012 Chrysler factory shop manuals and 20 multi-manual Chrysler Corp. CD's.

I was voted "Top expert" from 2010-2015 here at AllExperts, and have answered 20,000+ questions.

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Five decades as a 'do-it-yourselfer' on domestic and imported cars

Organizations
Yahoo Autos Group called The Chrysler Lebaron Club (co-moderator)

Education/Credentials
Degrees in Physics/bruised knuckles.

Awards and Honors
"Top expert" of 2010, 2011, 2012, 2013, 2014, and 2015 here at Allexperts. Quickest "average response time" at Allexperts (currently no. 1).

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