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Old 07-18-2019, 09:45 AM
Thread Starter
Join Date: Jul 2019
Posts: 1
P0420 Bank 1 and P0430 Bank 2* Codes on 2009 JKU

I have a 2009 JKU and am getting P0420 Bank 1 and P0430 Bank 2 (yes 2 not 1) codes.

I have been doing some research and this seems like an odd combination - at least it is to me.

She seems to be running good - has 129K miles. These are the only 2 codes present.

I did have an issue with loosing coolant and eventually had an overheating event that required me to replace the radiator. I did have a leak from the thermostat housing. All has been fixed and radiator replaced and no coolant leaks anymore. But these codes appeared well before the overheating event anyway.

Any suggestions would be appreciated.

StephenZ64 is offline   Quote
Old 07-18-2019, 12:33 PM   #2
Join Date: Jul 2013
Location: Hopkinton, MA
Posts: 335
Some possible things: Leak in the exhaust before the cat, bad O2 sensor(s), bad cat. A "real" mechanic can look at the O2 signals with a scanner and tell you what the issue is. I'm not a real mechanic, but I watch South Main Auto a lot and see Eric doing exactly that.

There are other possible causes. To me, a P0420 is a code that says "I am a Subaru".

Jack FFR1846 is offline   Quote
Old 07-18-2019, 06:25 PM   #3
Join Date: Jan 2019
Location: Round Rock, TX
Posts: 167
Most likely it’s your cats. Usually you envoke a rich condition and make sure the o2 sensors show it on a scan tool. Then you invoke a lean condition and make sure the o2 sensors show it. After that it’s almost certainly bad cats.

South main auto is great. Encourage you to search for any bad catalytic converter videos. He’ll show you the way.
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Old 07-18-2019, 06:43 PM   #4
Join Date: Mar 2017
Posts: 426
Assuming on the original 02 sensors. You can usually tell a cat is bad/sounds like rocks in a can when you hit it.

I just did the sensors on my 08 and have around the same mileage.

You will probably need new sensors either way so would do those first and see if that clears them up. Would be my bet since your still running with no apparent issues and bad cats are usually pretty apparent.

Good luck

Found a pic/mine were cooked.

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jeepjk1968 is offline   Quote

p0420 , p0430

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