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I have a 2001 Outback (2.5L) with 155k miles on it. The CEL came on last week, and it's the P0420 code (Bank 1) that I've been reading all about on this forum.

My mechanic told me that I need to replace the catalytic converter, and sent me to a local muffler shop which quoted me $950 for the part. He said that he would replace the O2 sensors afterwards if the light came on again.After reading a lot of the 0420 threads on this forum, I went to a different mechanic to ask about the code, and whether I should repair the O2 sensors before I replace the catalytic converter. The new mechanic told me the same thing as the old one -- that 95% of the time, the 0420 code means a bad catalytic converter, and that I should do that first. This contradicts everything I have read here, but both mechanics told me the same thing.

I haven't found a mechanic I've been really happy with since I moved here (I live in Texas now, and Subarus don't seem to be as common as on the west coast) and I'm not sure what to do at this point. I'm leaving in a few weeks to drive from Texas to Canada --it's a long drive (!) and I'm guessing I need to deal with this before I go. I haven't had any problems with the car other than the light going on (mileage hasn't changed, no egg-y smell, no backfiring).

If I do go with their advice, they've told me if I can find a cheaper catalytic converter online they'd be happy to install it for me. When I said I wouldn't know how to do this, they told me to 'just google it'. A friend who buys his parts online looked for me at autopartswarehouse.com and gave me part numbers--but when I enter the numbers on the website it say that it won't fit my car. I was told I need the front converter --I need the california emissions standards ones, which seems to make it harder.
I've looked on other website recommended here and come up with other options
Partsgeek.com : Basal 414-05192336 $321.10
Subarupartsforyou.com: Part# Sub3035 $499
But I have no idea how to tell which one I should or shouldn't get! I don't know very much about cars, and feel that if I go to buy parts online I'm just going to get scammed.

Sorry for the long thread, and yet another P0420 thread!
 

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you need to find an honest mechanic.

95% of the time is a correct number, but that is the number for how often it is a bad O2 sensor.

Lets start with the O2 sensors, since they would probably be replaced anyway. You are at the right mileage (over 100K) for the front sensors.

This isn't a long thread.

You can also go on your long trip without any issues.

If you do (I doubt it) need a cat, anything but Eastern Cats.
 

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However if you do need to replace the cats, you can buy them from here: RockAuto Parts Catalog

I would also replace the O2 Sensors before replacing the cats, ^^ rockauto also sells those btw. I'd start with the rear O2 sensor since it monitors the efficiency of the cats, and i've heard that it usually fails before the cats actually do.
 

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Actually the front ones fail first, the rears may never go bad as they aren't as exposed to volitile raw exhuast gasses.

Go OE if you can for the front O2 sensor, rears can be generic.
 

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Discussion Starter #6
Thanks for your help all!

So it sounds like I should ask them to replace the front O2 sensor first. Would it be best to just get them both replaced at the same time?

Finally, if I replace the sensors, then the mechanics should just re-set the code, and I could see if it comes up again? If the CEL light stayed off, I could assume that it was the O2 sensor and not the catalytic converter?

I wish I had a mechanic I trusted as well! I'm moving back to Canada, where I had a mechanic I liked a lot (but parts are so much more expensive there that if I needed a big repair, like the converter, I was hoping to do it here).
 

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If you had a really good diagnostician he could use a multimeter to read which O2 sensor is the issue.

Why not split the difference. Buy the sensors in the USA and have them installed in Canada?
 

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Hmmm....the second mechanic I took it to told me that he'd be able to hook it up to his machines and tell me if it was the O2 sensors or the converter. But then said it was 95% it was the converter, so I should just buy one and bring it in and he'd install it.

Maybe I should take it back and insist they run the test...
 

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The OBD port is just a tool. Did he just read the codes, or did he road test the car while reading the real time output of the O2 sensors? I bet he is just reading the codes. replacing the cat for a poor eff code is like getting a nose job to fix a runny nose.

I would ask him what machines he hooked it up to, I bet it is just a code reader.
 

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He didn't do either. He looked at the code print-out from my other mechanic. He then told me that he would be able to determine if it was the 02 sensor with his machines, but 95% of the time it would be the converter, so I should just buy the part (I took this to mean that he didn't think it was worth hooking it up to the machines to test it)....

After writing that out, I'm thinking I should try mechanic #3 to get the O2 sensors done. I should ask if they have the ability to road test it to check the sensors (is this the way I would phrase it?)
 

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Discussion Starter #11
Thought I would post an update here. The third mechanic I took it to also said I needed a new cat, but also suggested waiting until I had finished my cross-country move so that if I did need warranty repairs they would be close to home.

I ended up running a container of "Cat Clean" from Autozone through the gas tank with a tank of premium fuel before I started the cross-country drive and then a can of Seafoam 1/2 way through (the Cat Clean was the suggestion from Autozone when I went in to buy Seafoam after reading the suggestions here).

The engine light never came back on after my last visit to the mechanic (he turned it off to test it) and I just got a check-up here, 3500 miles later, and there is no error code anymore. So....no new cat, just a few fuel additives and it looks like I've avoided a major repair.

Thanks for the suggestions!
 

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hopefully it's gone for good - more often than not it comes back though. i'd plan on seeing it again within the year. i cleared a friends earlier this year and it came back about a month ago - so took 6 months or so but it came back.

could do just about anything...either way, it's a debacle of a code and you do not need a new catalytic converter.
 

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Hmmm....the second mechanic I took it to told me that he'd be able to hook it up to his machines and tell me if it was the O2 sensors or the converter. But then said it was 95% it was the converter, so I should just buy one and bring it in and he'd install it.

Maybe I should take it back and insist they run the test...
With proper maintenance, catalytic converters last a lifetime. Cats fail due to rich mix that is higher than the cat can handle, carbon due to rich mix or burning oil, overheating due to over lean conditions.

The majority of repairs that I perform to correct a P0420, which means nothing more than something is wrong with the performance of the engine and it is effecting the efficiency of the catalytic converter, is thermostat, sparks, fuel filter, pcv valve, vacuum leak repair and fill up with better gasoline.

Especially the gasolines this time of year where the fuel companies are switching the blends. About half the cars this last month with P0420 was due to the blend for winter. We're still too warm for winter blend.

Very rare is a catalytic converter replaced. 95% of the time is something else that is related to the way the engine is performing.

Find another mechanic. Or rather an honest technician. A mechanic throws on parts, a technician finds the real underlying problem. A new cat will only "hide" the real problem and for a short time.
 
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