Ray,
I had the Cat replaced last September for the same reason you replaced yours
(rattling). Could it be a bad O2 sensor? For what it's worth the truck seems to run
fine so it's probably not a large vacuum leak, although now that you mention it, it
does seem to be consuming a little oil.
Ray Irons wrote:
> Bob,
> I went and got my little book, which your local Auto Zone store should have
> done, that list's the all the generic codes, their meaning and probable
> causes for the code. P0420, according to the book I have, says:
>
> P0420 thru P0422
> Catalyst efficiency low bank one
> The oxygen sensors monitor the catalytic converters ability to store oxygen.
> Probable causes
> 1st. Catalytic converter defective (Failure possibly due to #2,3,or 4)
> 2nd Engine misfire or running condition
> 3rd Large vacuum leak
> 4th Engine oil leakage into exhaust-valve guide seals, piston rings
>
> Either way you go, it would seem you have a bad cat. How many miles do you
> have on the truck? I forget what the limit is but the manufacture has to
> warranty the cat as part of the emission system for, I think, 80K miles and
> 6 years. IF you are under the mileage, you may be able to get it replaced at
> the dealer for free. I had mine done a couple of years ago when I heard
> something rattling in the cat when the truck had over 50K miles on it. You
> also need to look at the other items on that list and see if any of them
> apply to your truck. Since you don't mention you had a code pulled for a
> misfire, (they would be P0300, random multiple misfires, P0301, misfire #1
> cylinder, etc.) A misfire doesn't seem likely. A vacuum leak should be easy
> enough to recognize. I found a troubleshooting guide that gave an easy way
> to find vacuum leaks. With the engine running, take a propane plumbers torch
> and open the valve but do not light the torch. Aim the nozzle around the
> hoses and intake manifold, wherever you suspect a vacuum leak. When the
> engine RPM picks up, you have probably found the leak. Engine oil leakage
> should also be easy to rule out if you keep a close eye on you oil
> consumption.
>
> Let us know how this turns out for you and what your solution is.
>
> HTH,
>
> Ray Irons,
> Dover, DE
> -----Original Message-----
> From: owner-dakota-truck@bent.twistedbits.net
> [mailto:owner-dakota-truck@bent.twistedbits.net]On Behalf Of bob
> Sent: Sunday, February 20, 2005 4:21 PM
> To: dakota-truck-moderator@bent.twistedbits.net
> Subject: DML: Trouble code P0420
>
> After getting a "CHECK ENGINE LIGHT" I went to Auto Zone and had the
> code pulled. They said it was a P0420. The print out gave the following:
> The PCM has determined that the catalyst system efficiency for Bank 1 is
> below threshold for the current engine operating conditions. (Bank 1
> identifies the location of cylinder #1, while Bank 2 identifies the
> cylinder of the opposite Bank). They were not very helpful in
> identifying possible solutions. Any ideas? Thanks
>
> Bob
> 99 Dakota
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