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Unread 12-19-2012, 01:10 PM   #1
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1998 ZJ 
Join Date: Jun 2010
Location: , NY
Posts: 594
p0420 code?

Hey guys so this is the second time in about 3 months now that I had a check engine light code come up and have it be P0420. I looked it up in my haynes manual and all it says is catalyst efficiency below required level. Does this simply mean that my catalytic converter is on its way out?

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Unread 12-19-2012, 01:26 PM   #2
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1998 ZJ 
Join Date: Aug 2012
Location: Sellersburg, IN
Posts: 327
That or one of the o2 sensors is reading incorrectly. If they are reading too close to the same reading it will trigger that code. Check cat for holes or rattles to make sure it is the cat.
1998 Jeep Grand Cherokee 5.9 Limited - Stone White - Stock for now.
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Unread 12-19-2012, 02:26 PM   #3
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1995 ZJ 
Join Date: Dec 2010
Location: Norman, OK
Posts: 2,311
Yes, your catalytic converter is basically not cleaning up the exhaust emissions to EPA standards. Simply put there may be nothing at wrong with it physically but the catalyst is degrading. I guess there is the very slight possibilty that the problem could be a sensor but to understand how the sensors read and what requirements are made to trigger the code that would be a far stretch.
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