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Hello and HELP! CODE P0420


Old 12-09-2007, 10:39 AM
DonnasDodge is offline
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Join Date: Dec 2007
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Default Hello and HELP! CODE P0420

Hello everyone and this is my first post on the forum. I love my truck although I haven't done a ton to it, just but 35" tires. Just wanted to say hey and I plan on being part of this family for awhile since I still have a lot of plans for the truck.

Anyway, sorry to jump in with a problem, but I have one. After a 800 mile trip to and from Reno, our truck threw a CEL. The code is P0420. I had this checked recently and it came up with the following:

Catalyst efficiency low-bank 1

The oxygen sensors monitor the catalytic converters ability to store oxygen.

Probable Causes
1.) Catalytic Converter defective (Failure possibly due to #2, 3, or 4)
2.) Engine misfire or running condition
3.) Large Vacuum leak
4.) Engine oil leakage into exhaust-valve guide seals, piston rings

Now some backstory. Right now with Christmas coming, I don't want to take it down to someone right yet with out trying to figure this out a little by myself. I have had people recommend replacing the O2 sensors, but after checking it looks as if there are 4 of them (2 before and 2 after the CC).

What would you guys recommend? I really would like to get this solved without having to shell out tons of cash right before the Holidays.

Thanks again for everyone's help.

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Old 12-09-2007, 04:14 PM
DonnasDodge is offline
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Default RE: Hello and HELP! CODE P0420

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Old 12-09-2007, 04:42 PM
CarGuyOhio's Avatar
CarGuyOhio is offline
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Default RE: Hello and HELP! CODE P0420

#2 should be out. There are codes that would show up for misfires

#3 should be easy to hear

#1 would require to to put oil in the truck often

May also help to state year, miles, engine, ect.
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Old 12-09-2007, 04:48 PM
Gone Fishin
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Default RE: Hello and HELP! CODE P0420


It would really help if we knew what exactly you are running. I'm assuming a 5.7L Hemi, In which case I would start out by checking for a vacuum leak, especially around the charchol canister and associated lines. It should be located under the truck in the frame rails behind the driver. The hoses are just plain old rubber, and if they crack much, you get a large air leak. Next, If you're not seeing blue smoke on startup, chances are the valve seals are ok. I would wait until you check out the vacuum possibility before I would spring for the O2 sensors (after the converters). How many miles, last tune-up??? etc.
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Old 12-22-2007, 11:06 AM
DonnasDodge is offline
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Default RE: Hello and HELP! CODE P0420

There are about 57k on the truck and its a 2005 Dodge Ram 1500 QDCB Hemi. Last tune up was about 900 miles ago, but will be needing to do the 60-75k service soon.

Which hoses should I check first? Is there a way of determining that it is a vacuum leak other than visual inspection?

Thanks again everyone for your help. Trying to avoid a fat charge from a mechanic to just figure out the problem, then another fat charge for the solution.

Merry Christmas!
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Old 01-12-2008, 07:07 AM
Rabies is offline
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