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Old 12-25-2012, 10:38 PM   #1
ScubaruImpreza05
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Question P0420; or what catalytic converter to get?

2006 Subaru Impreza 2.5i Sedan.

So, I have been getting this code for the last 20,000 miles or so. I have an Actron that I scan the ECU with and clear the code out when I feel like having cruise control back. Usually I could clear the code and it might stay away for 2,000 miles or so and then come back at random. Well it finally is done playing this game apparently. The code comes back within 100 or so miles of clearing each time.

What I have done so far:
1.) used Actron to read/clear codes as they come and mentally logged codes and how often
2.) Bought a tactrix Cable and used ROMraider to pull graphs, and analyze my sensor data
3.) Bought completely brand new Denso o2 sensors roughly 10,000 miles ago.

The new sensors didn't change much, maybe widened the intervals between codes for a few months. The sensors I pulled out looked like the engine was burning clean, basically what they should look like on a healthy engine. The space between code throws gradually became smaller and smaller until it is almost immediately after the intial mileage on the ECU reset.

My only other thoughts are maybe spark plugs? Would worn out plugs cause the P0420? I can't remember how many miles ago I switched from the stock plugs to the Copper plugs that were suggested on here, but it could easily be over 10,000 miles ago.

If the plugs wouldn't cause it, I'd be confident in saying it is the actual catalytic converter. Any suggestions on what to gety and where? Obviously I could go to the stealership and get raped on price, but I usually do my own work and I like getting best bang for buck.
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Old 12-26-2012, 07:30 AM   #2
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Bad cat for sure.
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Old 12-26-2012, 07:55 AM   #3
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My friend has UEL headers and a gutted cat on his 05' rs...he elected to simply disable the code from romraider, no more po420, but since the rear o2 effects fueling for the 05' and newer models i wouldnt just ignore the code.
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Old 12-26-2012, 11:47 AM   #4
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That's what I figured. So, here is a link with a diagram: http://www.ezsubaruparts.com/parts/2...iagram=7591281



So I am getting from this, that my front cats are built into the exhaust assembly that comes from the port on the heads....and that there is a secondary (downstream?) catalytic converter as well, components 1 and 6. This would total $1,090.00 not even shipped. Screw that.

Any options? Is there a standard, such as the catalytic converter that goes bad often is the rear one? or something of that nature? I don't want to go UEL because of sound but I also don't want to spend $exas on a car I want to just use for business and regular commuting. I think I can monitor each o2 sensor individually with the Actron (I no longer have the Tactrix unfortunately) so is there a set of values I can look at on the monitor to see if it is my front cat or rear cat? I believe the sensors measure in voltages.
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Old 12-26-2012, 12:24 PM   #5
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You are correct sir, your front cat is part of the header assembly. It's most likely that the rear cat is whats gone kaput. The hands down cheapest solution is to ask around your local community to see if anyone has a laptop and a tactrix cable. You can edit your ECU to simply turn off the code and be done with it. Thats what I did with mine (06 2.5i) a few years ago and never bothered me since.
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Old 12-26-2012, 12:27 PM   #6
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Also, if you replace with a universal cat or similar, you will still likely throw the CEL. Since there will likely be a change in flow rate the O2 sensors will ultimately be confused since the ECU assuming flow rate through OEM spec exhaust parts.
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Old 12-26-2012, 12:44 PM   #7
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Quote:
Originally Posted by treksofar View Post
The hands down cheapest solution is to ask around your local community to see if anyone has a laptop and a tactrix cable. You can edit your ECU to simply turn off the code and be done with it. Thats what I did with mine (06 2.5i) a few years ago and never bothered me since.
since the OP said they have the cable and software, this is an easy solution. and if the OP doesnt need to pass emissions readiness inspections this would be a permanent solution until the cat physically failed in some way.
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Old 12-26-2012, 12:47 PM   #8
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it still shows as "ready" with the code disabled. Massachusetts has done away with the sniffer test for years and I pass every time .
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Old 12-26-2012, 10:34 PM   #9
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Does anyone know if you can pull off getting an equal length header without any cats in it, and then custom weld in 2 cats aftert the header and pass emissions?

I was thinking of getting something cheap (and I know you get what you pay for) like THIS and buying 2 separate Cats and having a local exhaust shop make everything fit to save some money. My chief concern is passing emissions...because this is my only mode of tranportation and I can't be illegal.

EDIT: Actually, if anyone has a stock 06-07 header and downflow cat they could part with, please let me know. I'm not finding them anywhere and I have no good junkyards near me

Last edited by ScubaruImpreza05; 12-26-2012 at 10:53 PM.
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Old 12-27-2012, 10:26 AM   #10
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Quote:
Originally Posted by ScubaruImpreza05 View Post
Does anyone know if you can pull off getting an equal length header without any cats in it, and then custom weld in 2 cats aftert the header and pass emissions?

It depends what type of emissions testing you have to pass. If it's just an OBD readiness monitor test then apparently just turning off the offending code will allow the ecu to show "ready" as trek says. If it's a sniffer test it's a gamble.
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Old 12-27-2012, 11:20 AM   #11
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I'll ask a stupid question, just to (possibly) save the OP some trouble. Where are the O2 sensors located? Stealing a picture from another thread, here's the header:


So I can see upstream and downstream O2 sensors there. Is there another O2 sensor downstream of the 2nd cat (or maybe another pair of O2 sensors on either side of that 2nd cat)? If there are just the 2 O2 sensors in the header, then I think the cat in the header has to be the culprit, since the O2 sensors aren't monitoring the downstream cat at all.
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Old 12-27-2012, 11:36 AM   #12
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Quote:
Originally Posted by Patrick Olsen View Post
I'll ask a stupid question, just to (possibly) save the OP some trouble. Where are the O2 sensors located? Stealing a picture from another thread, here's the header:


So I can see upstream and downstream O2 sensors there. Is there another O2 sensor downstream of the 2nd cat (or maybe another pair of O2 sensors on either side of that 2nd cat)? If there are just the 2 O2 sensors in the header, then I think the cat in the header has to be the culprit, since the O2 sensors aren't monitoring the downstream cat at all.
b

I replaced them So I think I recall I could only find 2 sensors. One is located in the front of the engine (I actually was able to install it without jacking the car up at all) and the other is downstream but my brain fails me at this time. One sensor is coated orange and one is coated gray. Pictures of the actual sensors I replaced and new ones:

EDIT: Work blocked all pictures somehow so I can't see them except for on my phone. I just saw Patricks and yes I'm sure that is my header and that was the locations of the 2 I replaced. I will go see if there is another downstream over lunch, but I want to say no since I think I bought all available exhaust sensors.


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Old 12-27-2012, 11:53 AM   #13
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Old 12-27-2012, 12:02 PM   #14
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You can just cut the code out with romraider, and set your readiness bits to 1. Get rid of the cats.
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Old 12-27-2012, 01:04 PM   #15
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The 2 sensors I replaced:






Both are in some forms attached to the headers. I assume the orange is the AFR sensor and the rear is the O2 sensor. I could not confirm if there was a sensor in the mid pipe area somewhere as I couldn't get under the car, can someone confirm?
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Old 12-27-2012, 01:58 PM   #16
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That is it. you only have 2 and the yellow one goes first.
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Old 01-02-2013, 08:03 PM   #17
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Where's the cheapest place to buy an OEm header? No one seems to have any spare/used ones around and I need either a used one or cheap OEM
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Old 01-02-2013, 08:34 PM   #18
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Quote:
Originally Posted by ScubaruImpreza05 View Post
That's what I figured. So, here is a link with a diagram: http://www.ezsubaruparts.com/parts/2...iagram=7591281



So I am getting from this, that my front cats are built into the exhaust assembly that comes from the port on the heads....and that there is a secondary (downstream?) catalytic converter as well, components 1 and 6. This would total $1,090.00 not even shipped. Screw that.

Any options? Is there a standard, such as the catalytic converter that goes bad often is the rear one? or something of that nature? I don't want to go UEL because of sound but I also don't want to spend $exas on a car I want to just use for business and regular commuting. I think I can monitor each o2 sensor individually with the Actron (I no longer have the Tactrix unfortunately) so is there a set of values I can look at on the monitor to see if it is my front cat or rear cat? I believe the sensors measure in voltages.
You won't be needing #6 as this is a resonator and as such is not monitored (no sensors here) only the ones you have replaced as you stated. the only right way is new cats which is a real pain in the wallet?? Just quoted someone at work and it was about $750 fitted, and I work at a stealership!!
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Old 01-08-2013, 12:42 PM   #19
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Don't Cats have a 10yr warranty?
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Old 01-08-2013, 10:19 PM   #20
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And 80k^ I think pzev's are different though
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Old 01-14-2013, 11:05 AM   #21
wmdoucette
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No mention of Emissions systems Coverage for US in 2006. Canada has 8yr, 130000km Emissions systems coverage. Might be worth a try though, talk to a Dealer service manager.
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