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My check engine light came on and this was the code

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Common.

 

I have had excellent luck running Seafoam thru a vacuum hose to fix this for thousands of miles.

 

For the price an option I'd use rather than replacing the cat(s).

 

Do a search.  Oftgen discussed here.

 

Starting in mid 2000's I believe it seemed to get less effective - teh Seafoam thing, but considering alterntives still worth a ashot.

 

Besides - it creates an impressive white smoke cloud.  Do it somewhere where yopur meighbors won't think your house is on fire.

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looks like there is a second code on that reader - top right corner reads 1 / 2 (one of two?) - what is the other one for?

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looks like there is a second code on that reader - top right corner reads 1 / 2 (one of two?) - what is the other one for?

 

Same code, it was just more description

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Catalyst inefficiency - rear O2 sensor driven code.

 

Very common and difficult to properly repair as there are many causes, very few mechanics track down the cause.  Most shops will say new sensor and catalytic converter, which isn't the proper repair and extremely expensive. Subaru catatlyic converters typically last the life of the vehicle (except for rust..LOL) and shouldn't be replaced unless they've been actually tested/verified.

 

You can drive indefinitely with this code (if your state allows it that is). The ECU doesn't use that sensor for operation, you can literally cut it off and the car will run fine - like 1980's Subaru's which didn't even have this sensor or code and had no problems reaching insanely high mileages.


Here's some information on how to approach this debacle of a code:

 

1. fix any exhaust leaks - they can trip it.

2. cleaner of your favorite type, sea foam or MMO are good anyway, so try those first. (be prepared for massive smoke screen with seafoam - this is normal, but it won't look like it!

3. ignition tune up might be a good thing if it's due anyway - spark plugs and wires - NGK plugs and OEM wires or at least really good wires - these engines aren't too forgiving otherwise.

4.  make sure you don't have cheap/bad gas

 

if those don't alleviate it then you're left to figure out a proper diagnosis...which is something few people do, or do a work around.

 

1.  the $5 fix is to simply install an extender in between the sensor and exhaust, this works a high percentage of the time.  like this:

http://www.ebay.com/itm/HHO-Small-O2-Spacer-Adapter-Oxygen-Sensor-Extender-02-Bung-Extension-M18-x-1-5-/171044979424

there are a variety of styles, some with 90 degree bends if you don't have much room.

 

2.  the proper fix is difficult and i've never heard of a mechanic/dealer that does it but here's an in depth overview of the possible causes and in depth diagnosis: 

http://www.subaruoutback.org/forums/66-problems-maintenance/49537-p0420-diag.html

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As a followup to GG's info I have some folks with VW 1.9t's that must run 89 octane (which is recommended in a few of them anyways) and/or caon't buy cheap gay like a local convenience store or grocery store chain (Get-Go or Sheetz) or the light will come on.

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Same code, it was just more description

 

Gotcha - page one of two.

 

davebugs - dont know what you guys in PA have for gas, but 89 octane IS the "cheap" stuff around here ("cheap" being a relative term with prices as they are).

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I'm been filling up with 87. Should I be using a higher octane? I live on the east coast.

 

I used to live in Colorado, so maybe that's what got me in the habit of using 87.

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so many things can cause that code.

 

definitely get every maintenance/tune-up issue taken care of - make sure the plugs/wires are good, etc.

 

seafoam treatment is a good suggestion.

 

clear the code and see how quickly/if it returns.

 

DO NOT change the cat. converters.

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Gotcha - page one of two.

 

davebugs - dont know what you guys in PA have for gas, but 89 octane IS the "cheap" stuff around here ("cheap" being a relative term with prices as they are).

87 is the lowly standard here.  Of course ANYTHING with Ethanol that they force on us sucks.  I saw at the local outdoor power equipment place they actually sell fuel for weed wackers n stuff by the quart for like 8 bucks.  NO Ethanol.  SOme folks that owuld be an excellent idea versus it eating the fuel lines every year and gumming up the carbs (ask me how I know!).  I jsut use both of mine too much.

 

ALso the Seafoam cleans the cats and both O2 sensors.

 

But yea - a good basic tunup and OEM wires on the 2.5 are excellent idea's.

 

You're very likely to find the real problem doing basic maintenance things and Seafoam and still be way under what new cats would cost.  ALso remember IMO aftermarket cats only seem to last a year or two and OEM are very expensive traditionally.

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I had new spark plugs and new original spark plug wires put in a couple months ago, so I know that's not the problem.

 

I'll try the seafoam. Can I just add it to the gas?

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gas shouldn't matter unless your ECU is calibrated differently, etc....if you recently moved East you may want to disconnect the battery and let it relearn everything.

 

seafoam is generally added to the intake manifold...but i think you can add it to the gas as well.

adding to the intake cleans the throttle body, intake runners in the heads, and valves.

others have done it more than me so wait for their advice.

 

personally i'd probably MMO the gas and Seafoam the intake...but not sure if anyway is better and i've never really seen it "work".

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gas shouldn't matter unless your ECU is calibrated differently, etc....if you recently moved East you may want to disconnect the battery and let it relearn everything.

 

seafoam is generally added to the intake manifold...but i think you can add it to the gas as well.

adding to the intake cleans the throttle body, intake runners in the heads, and valves.

others have done it more than me so wait for their advice.

 

personally i'd probably MMO the gas and Seafoam the intake...but not sure if anyway is better and i've never really seen it "work".

 

What exactly does MMO the gas mean?

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Seafoam is best into a vacuum line, in the tank won't hurt though.


Does produce SERIOUS white smoke if done correctly.

 

Since I'm not worried about cumbustion chamber I'd use vacuum boost line because I could neve rfind a candidate that worked for me by the throttle body.

 

Now the chain places have aerosol cans that you can use and place on throttle body and replace airbox.

 

The simple can used to tell you to stall the car when the can was almost done IIR.  Then let it set 5 minutes and take it for a drive (killing all local mosquito's).  I still woudl take that route even though I believe the instructions are different now.

 

I've only tried the aerosol cans on a Toyota RAV4 and they make it very difficult due the throttle body replacement half was down engine near firewall on drivers side.

 

I don't realy work on cars much anymore and haven't tried the new expensive aerosol can on a SUbaru.

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My 2000 legacy has been running fine since 2007 with the p420 code on. Had headgaskets done at 135K and now just last week at 230k. Was hoping that the latest fix would make the 420 go away. It didn't so I will live with the little yellow light on and just check periodically to see that nothing new has popped up.

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I live up in upstate NY and just recently found out that the Fast Trac gas stations sell non ethanol gas, It cost a bit more but it's defiantly worth it!!!

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