2006 chrysler 3.5 300

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Feb 6, 2009
Hi I have this car with 75k on it got it from original owner, the code P0420 came on I reset it with scan tool. it will come on again the car uses oil in between oil 3.5 engines are know for that. The car has plenty of power so cats are not completely clogged. Why would the cat be going so soon and has anyone with this engine 3.5 had the same problems?
I have a friend that owns a garage the system is all stainless steel no leaks, I know theses engines use oil just wandering if that is the cause of the check engine light coming on!
P0420 is usually O2 sensors, there are usually sensors before and after the cat. Depending on the engine there may be 2 before and 2 after. At least that was my experience with the Toyota. You may need to check the forum specific for your car manufacturer to check with their experience fixing this code. BITOG is more of a generic forum for this type of issue.
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As said previously, likely an O2 sensor. Some say to replace them all at once if you can, some say just replace them as they go bad. If I can find them all fairly cheaply, and its on a car/truck with a lot of miles or age, I do them all when one fails. I've had good luck with Denso and NTK. I believe the 06 300 V-6 gas 2 upstreams and 2 downstreams and they are all the same model of sensor. You can get NTK's for 25 bucks at RA.
Ok Thanks there are 2 sensors on the cat one before and one after any idea as to which one could be bad?
Inspect them first for loose or broken wires, etc. I generally suspect the downstream first, but the only way to really tell is with a scan tool that tells you. Some do and some don't. Sometimes AZ and other auto parts places will scan it and tell you if you buy the part there. There are ways to test them with voltmeters, etc. if you google it.
Originally Posted By: HoosierJeeper
Only use NTK on anything Mopar! O'Reillys carries them.
Yup. Lots of guys on the Jeepforums who use Bosch or something else and have issues or poor fuel economy.
From what I've read, worry about the ones upstream first. They are usually the ones that go bad and are usually easier to replace. I know the downstream one on my Corolla was a real bear to get out. Changing the O2 sensors did fix the P0429 code in my Corolla.
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