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Discussion Starter #1
I pulled this code at the autoparts store, and then googled up the issue. Google returned that this was typically the front O2 sensor, which I purchased but have not yet installed.

After a quick check here, I see on the forum where people are saying that this code usually means the cat is bad. Am I chasing the wrong ghost with the front O2 sensor? Should I do the rear instead?

What else should I try? I’ve seen people say to clean the AF sensor and MAF sensor. Is the AF the same as the O2? Can those be cleaned instead of replaced?

Any chance running seafoam thru the intake would help? I have an emissions test coming up soon. As in “end of the week” soon. LOL.
 

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If you just want to pass inspection, get the spark plug spacer on the new O2 sensor or whatever they call that.

It's the rear one that turns on the check engine light. But the computer is comparing the front and rear so if the front one isn't right, you will get problems.

If you want to actually fix the problem, look here: P0420 Diagnosis

My personal experience has been that I needed to change the catalytic converter.

Tom
 

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There is a good chance it isn't the sensor or the cat. There are a multitude of things that can cause that code. I had that code and I believe tdelker recommended a thread on the outback website. A lot of reading later I solved my problem by cleaning all the grounds. Cheap easy fix. You have to solve the problem that is causing the code. You can put new sensors and a cat in and the code will be back because they were not the root cause of the code.
 

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Discussion Starter #4
Thanks, Tom. Ultimately, I would like to fix the issue, provided the repair isn’t the thousands of dollars required for a new cat. In the short term, I need to pass emissions.

Spark plug spacer? I tried to search this on the forum, but probably aren’t using the correct verbage.
 

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Discussion Starter #7
Well I did manage to do the install of the above trick but after clearing codes I then threw p0137 and p0157. (I think that’s right). Does that tell me anything new? I can just as easily uninstall and get an ermissions waiver based on the cost of a new cat. On the other hnd, if it points to a need for new 02 sensors, I can also go that route.
 

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I would say the extension is the issue with the new codes. I check voltage on the rear O2 sensor to see if the issue was the cat. Voltage was all over the place on drivers and steady on passenger. Swapped sensors and still got crazy voltage on drivers side. Changed cats and all codes went away. I had previous code for bad rear O2 on passenger side so I knew the readings on it were good since I had got a new sensor and that code went away. Thats why it pointed to cat once I swapped sensor side to side. There are many options for cats on ebay that are more cost effective than going dealer route. I replaced both sides for under $900 canadian.
 
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