Code P0420?

Tiny
BEETLEPUNK21
  • MEMBER
  • 2015 DODGE JOURNEY
  • 2.4L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 160,000 MILES
Hello, I am getting a P0420 code, and I took a picture of the oxygen sensor information and I’m wondering if you could help me interpret it. I’m not very good with the information. Is sensor number two bad?

I’m hoping I don’t have to replace the entire catalytic converter.
Friday, April 18th, 2025 AT 9:22 AM

14 Replies

Tiny
STEVE W.
  • MECHANIC
  • 14,747 POSTS
Pull up the bank one sensor 1 voltage. Then the bank one sensor 2 volts, select those and switch to graphing mode. Now look at the data. Sensor 1 should be switching rich lean rapidly. Sensor 2 should be an almost flat line with small changes. If it looks like the data from sensor one the converter isn't working. With the codes you have I would say the converter is bad.

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms
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Friday, April 18th, 2025 AT 7:38 PM
Tiny
BEETLEPUNK21
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Have you ever had anyone use cleaners like Cata clean or seafoam or anything with success?
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Sunday, April 20th, 2025 AT 3:59 PM
Tiny
STEVE W.
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If it's a very intermittent code that only pops up once a month, they might help, usually they don't. Where they work is on a vehicle that hasn't baked on the contamination or had physical damage in the converter. The Journey though uses a poor design where the monitor sensor is in the middle of the converter so that the entire second half of it could work fine, but the upper half is bad. Unfortunately, there is no way to change that. I just put a set of OEM units on one that wiped them out from burning oil. The ones that came off looked like they were covered in tar over the honeycomb.
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Sunday, April 20th, 2025 AT 4:56 PM
Tiny
BEETLEPUNK21
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This is like the third time I am trying to upload these videos. For some reason it’s not going through. I might just have to try to load them separately each time.
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Monday, April 21st, 2025 AT 4:33 AM
Tiny
BEETLEPUNK21
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It looks good at the start but then at the last video it looks like sensor number two is doing what sensor number one is doing.
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Monday, April 21st, 2025 AT 4:34 AM
Tiny
BEETLEPUNK21
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Video 2
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Monday, April 21st, 2025 AT 4:36 AM
Tiny
BEETLEPUNK21
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Video 3
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Monday, April 21st, 2025 AT 4:37 AM
Tiny
BEETLEPUNK21
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Video 4 (last video)
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Monday, April 21st, 2025 AT 4:38 AM
Tiny
STEVE W.
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Yeah that looks like the converter isn't working at all once it warms up. It also looks like sensor 1 is sluggish. Unfortunately, the repair would be a new converter and sensor 1.
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Monday, April 21st, 2025 AT 6:38 AM
Tiny
BEETLEPUNK21
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Okay, thanks Steve. I will order a new converter and sensor. Appreciate you!
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Monday, April 21st, 2025 AT 9:36 AM
Tiny
STEVE W.
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Sit down when you ask the price? Let us know the outcome please.
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Monday, April 21st, 2025 AT 1:30 PM
Tiny
BEETLEPUNK21
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I bought a new converter from rock auto for $200 and installed it. I kept the same oxygen sensors from the old converter. Here is the new information from the scan tool.
How does it look? The engine is already at operating temperature.

I just noticed that the image is uploaded upside down. I don’t know why it’s doing that. Hopefully you can still read it properly.
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Sunday, May 4th, 2025 AT 5:16 PM
Tiny
STEVE W.
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You must not be in a C.A.R.B. State, lucky you. I just did one on a 2.4 last week, $1,160.00 from the dealer! In the first video you can see the sensor voltage for S1 and S2 don't track with each other, that is a good thing. Look at the difference between that and the videos you posted earlier where they were almost in sync with each other. With the mileage you might want to change the upstream sensor just to get better control but if it isn't using oil and the sensor didn't look like a charcoal briquet when you had it out it could be okay.
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+1
Monday, May 5th, 2025 AT 12:24 PM

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