P0420 Code - Catalytic Converter or O2 Sensor?

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Oct 14, 2020 | 09:42 AM

#11

Seanjordan20

Been Around A Long Time Member

Joined: Jun 2017

Posts: 1,225

Check your #4 plug to see if there's oil or if you need new plugs. If all ok swap the coil to see if the misfire moves. If it does the coil is bad. At that mileage the coil should be good

Oct 14, 2020 | 05:01 PM

#12

Ohenry

Joined: Oct 2020

Posts: 4

From: NW Florida

Thank you.

Quote:

Originally Posted by Seanjordan20

Check your #4 plug to see if there's oil or if you need new plugs. If all ok swap the coil to see if the misfire moves. If it does the coil is bad. At that mileage the coil should be good

the previous owner didn’t change the plugs so I’ll swap them all out and switch coils from 3&4 and see what happens. Thank you for the input. Any suggestions on the 420 or is this a contributing factor that needs to be addressed first.

At 2500 rpm

Last edited by Ohenry; Oct 14, 2020 at 05:08 PM. Reason: Add photo

Oct 14, 2020 | 05:18 PM

#13

Seanjordan20

Been Around A Long Time Member

Joined: Jun 2017

Posts: 1,225

Address first. You'll be able to tell if you need a new valve cover kit if there's oil on the plugs

Oct 14, 2020 | 08:00 PM

#14

Ohenry

Joined: Oct 2020

Posts: 4

From: NW Florida

Thank you. I’ll get this done Saturday.

Oct 15, 2020 | 01:00 PM

#15

partialresponse

Thread Starter

Newest Of Newbies

Joined: Aug 2009

Posts: 15

Quote:

Originally Posted by Ohenry

I just purchased a 2010 (172K miles) and was told the service engine light was on and the car would not accelerate but then it went away and the SEL went out. Pulled the codes last night. P0420 and P0304; #4 misfire. Cleared the codes and they came right back on subsequent scans. Any recommendations? I experienced the same O2 voltage as OP.

I replaced both oxygen sensors at about 140k miles, and after clearing the P0420 code it hasn’t reappeared in over 10k miles. Catalytic converter input and output temperatures were clearly not a good indication of the source of my P0420 code.