PO421

Tiny
QUINNY24
  • MEMBER
  • 1942 MITSUBISHI
I have a 2000 Montero Sport. Got code PO421 and have sequentially replaced all 4 O2 sensors in addition to having a complete tuneup including a new timing belt. After replacing the 4th and final O2 sensor I thought all was well but 2 weeks later the same code reared its ugly head. Where do I look from here, could it be my cat? The car seems to run just fine.
Friday, December 15th, 2006 AT 7:31 PM

4 Replies

Tiny
CARUNDELL
  • MECHANIC
  • 602 POSTS
Hey Quinny,
p0421 is a catalytic converter efficiency code and since you have already replaced the 2 post cat O2's then it sounds like you have a cat that has failed. Which bank is it?

Chris
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Saturday, December 16th, 2006 AT 4:35 AM
Tiny
QUINNY24
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PO421 is bank 1. How many cats are there on this thing two or three?
I wonder how long I have til it goes bad on me.
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Saturday, December 16th, 2006 AT 1:06 PM
Tiny
QUINNY24
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What is the difference between this code and PO420?
PO421 says "warmup catalyst efficiency below threshold (bank 1)" and
PO420 says"catalyst system efficiency below threshold (bank 1)"?
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Thursday, January 25th, 2007 AT 2:05 PM
Tiny
QUINNY24
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Just for everyones info. I ended up taking my Montero Sport to Meineke and was told I needed a new cat, the owner of Meineke told me a direct fit would be $900 plus but that he could find one for much less than that probably even half. Well after searching for 2 days he calls and tells me he can't get an aftermarket direct fit and I need to get it from the dealer for the original estimate of $900 plus.
I am starting to get very bitter at this thing, for one thing I bought a car with California emissions (who ever checks for that when they go out to buy a car in Pennsylvania). Well at 44 I'm still living and learning LOL
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Wednesday, February 14th, 2007 AT 10:39 AM

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