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Dodge Repair/P0420 code


QUESTION: Hi Roland-

Check engine light came on on my wife's 2004 Dodge Grand Caravan. Mechanic said it was code P420 and it means the catalytic converter has failed and needs to be replace. The vehicle has only 81,000 miles and I would think it would have lasted longer. Anything simpler and cheaper to check that might also cause this code?


There are several possible causes other than a failed converter, but the converter should be visually checked for signs of damage, or also listen to it when the engine is running (then rev the engine) and if you hear a rattling sound from the front of the converter that would be indicative of a loose honeycomb unit inside the converter which is a failure mode.
The other possibilities are if there were a new/newer rear oxygen sensor coupled to a degraded front oxygen sensor that will often set this code. An exhaust leak between the engine and the front sensor or between the front sensor and the rear sensor can cause this code. If there was also a code for too lean a mixture or a faulty oxygen sensor then those codes should be corrected first to see if that also corrects the 0420. Finally excessive smoke from the engine due to some mechanical problem with it should be corrected first.
So consider whether any of those apply and if so tend to them first.
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---------- FOLLOW-UP ----------

QUESTION: Thanks for your quick reply.

Nothing has been done to the van as to replacing any sensors. I will get under the van to check for damage and listen to the exhaust. There had been no change in performance, noise, gas mileage, etc... although an oil change was done about 500 miles ago. It just turned on while we were driving earlier this week.

See if the converter looks/sounds OK and also you might visually check the oxygen sensor at the far end of the converter and the oxygen sensor at the exhaust manifold, and of course listen for exhaust leaks along the pipes from the engine to the converter.

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Roland Finston


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.

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I have do-it-yourself experience (50+ years) and a library of 100 1982-2011 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.


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

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

Degrees in Physics/bruised knuckles.

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