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2008 Outback 2.5i Limited, 2010 Outback 2.5i CVT
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Discussion Starter · #1 ·
Hi all, as you will see, it's my first question....

After reading most if not all of Cardoc's 1000+ page bible on the P0420 codes, and doing much of the testing (as best I could), I thought I'd ask for a bit of advise. Let's assume that the 420 code keeps showing up. FF, we bought a 2008 OBW 2.5i for our 18yo to take to Colorado (420 code amirite?). 120K miles, decent deal. Replaced Rack and then it broke a strut the day before she left. (wife then picked her up a 2010 OBW much to my chagrin).

Anyhoo, I am trying to decide what's next. Of course the 0420 keeps coming on, and I CAN'T USE CRUISE - DRIVES ME NUTS. I'm a VW guy,so this has never been an issue.

I've done the following: Used 91 octane from a reputable station (noting that 90% of the gas comes from the same terminal). Ran some seafoam, had it checked on the Dealer computer, etc. They recommended a Cat. of course. Dealer also told me that they would need to drive my car around for an hour or more to see the O2 sensors are working correctly. Went to a local muffler/exhaust shop and he said ($1000() to replace, but he said he wasn't sure that would fix the problem, and was honest about it. Another "Ol boy" who works on a few Subarus said it probably is the Cat.

So the question to you more experienced folks is this: I'm prepared to get new cats and put them on myself. No biggie. I'm semi mechanical! If I go this route I will also get new AF and O2 sensors, as it might make sense? Will the installation of this help eliminate the problem. I know from Cardoc's post, that the answer is "maybe."

Other stats: I called previous non subaru dealer who sold car to guy I bought it from and they said Timing belt, etc, including head gaskets planed heads, H20 pump etc was all done in Feb 16. There is red "silicone" around the gaskets at the heads, cat gasket and rear gasket to the tailpipe. ??? good or bad.

I just filled up, and the last tank got 18.4 MPG around town, with one short trip on the highway. Exhaust at the tip has some carbon buildup, enough to smear on your finger, with a gassy smell. VW is dry at the tip, with no residue.

Hesitation upon stopping at a stop sign and then taking off, as if it wants to die.

I have an OBDII interface with iPhone app, and it had the "CAtalyst" temp at 1200 degrees at 70 on the highway. Don't know what the heck that means, but there ya go!

I can't think of any other issues tied to this, but I would love to just put new cats on and solve the problem! or whatever!

Any advice is appreciated. Except telling me I'm a moron. HA!
 

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On the Super Mod Squad
2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
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26,951 Posts
step 1, do not think about buying and replacing cats, until all cheaper options are thought out.

step 2,...what other codes are there. the in board diagnostic reader in that particular car may show more then hand helds:

http://www.subaruoutback.org/forums...9-how-read-diagnostic-trouble-codes-dtcs.html

if you have a flashing check engine light, that is a misfire and that makes for a p0420 easy. (flashing cc = what???)
 
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2008 Outback 2.5i Limited, 2010 Outback 2.5i CVT
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69 Posts
Discussion Starter · #3 ·
Thank you EagleEye.

I might start with the AF and O2 sensors then. No noise per se from the Cats, so maybe the sensors would cure it.

I'll look into that Diagnosis Code procedure. Almost looks like fun!

I'll edit the original post, sorry for the confusion. Flashing Cruise Control light, not CEL light. Believe me, I know the connection between the two! LOL
 

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Discussion Starter · #4 ·
Sorry for confusing wording. Flashing CC = Flashing Cruise Control light, of course tied to the CEL. Cheers!
 

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(formerly) 03 H6 OBW , (presently) 06 WRX Sportwagon & 2021 Honda CR-V
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if you can get a clean view, use an infrared therm. and measure the warmed-up temps of the pipes in front and at rear of the cat while idling. If the temp is hotter (100 degrees or so ?) at the rear, cat is 'lighting-off' and may be OK. So, try a new rear O2 sensor?

if rear of cat is same or cooler temp, and you have confirmed there's no tune-up or A:F problems and no exhaust leaks - may be time for a cat?

almost all modern cars disable cruise, traction control and some other functions if a CEL is lit.
 

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Discussion Starter · #6 ·
step 1, do not think about buying and replacing cats, until all cheaper options are thought out.

step 2,...what other codes are there. the in board diagnostic reader in that particular car may show more then hand helds:


if you have a flashing check engine light, that is a misfire and that makes for a p0420 easy. (flashing cc = what???)
eagleeye, I was hoping so much to get something useful out of this, but got the dreaded P----. It was fun while it lasted!
 

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Discussion Starter · #7 ·
if you can get a clean view, use an infrared therm. and measure the warmed-up temps of the pipes in front and at rear of the cat while idling. If the temp is hotter (100 degrees or so ?) at the rear, cat is 'lighting-off' and may be OK. So, try a new rear O2 sensor?

if rear of cat is same or cooler temp, and you have confirmed there's no tune-up or A:F problems and no exhaust leaks - may be time for a cat?

almost all modern cars disable cruise, traction control and some other functions if a CEL is lit.
Thank you my friend. I attempted the temperature procedure yesterday, but was having difficulty shooting around the heat shields. I'll do it again here in a bit to see what I get. Think I'll put it up on the blocks to get under it!

I guess first / next step is to get an O2 sensor and a real live Subaru AF sensor. That will put me about $250 out, and then if that doesn't fix it on t the cats!
 

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eagleeye, I was hoping so much to get something useful out of this, but got the dreaded P----. It was fun while it lasted!
that on board diagnostic thing in the 2005-2009 cars sometimes needs a few tries to get it to spill its tale. ...
just like a handheld, or the things I use with my phone or laptop. those sometimes take a few tries to get with it.

I have changed the rear o2 sensor 2x on my 2.5 car, for P0420 blues, still running the original factory cat. each time with a Denso branded one.
(those cost about $70-75 bucks on amazon or rockauto).

NGK = NTK ,...I have not tried those yet but that is a quality company (the biggest spark plug company in the world). ... I don't think I would bother with buying a subaru o2 sensor, (they are repacking Densos, or maybe today NTK which is a new label to the aftermarket).
 

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Discussion Starter · #9 ·
that on board diagnostic thing in the 2005-2009 cars sometimes needs a few tries to get it to spill its tale. ...
just like a handheld, or the things I use with my phone or laptop. those sometimes take a few tries to get with it.

I have changed the rear o2 sensor 2x on my 2.5 car, for P0420 blues, still running the original factory cat. each time with a Denso branded one.
(those cost about $70-75 bucks on amazon or rockauto).

NGK = NTK ,...I have not tried those yet but that is a quality company (the biggest spark plug company in the world). ... I don't think I would bother with buying a subaru o2 sensor, (they are repacking Densos, or maybe today NTK which is a new label to the aftermarket).
Good Info. Ordered the Denso models last week from rock auto, and they came n Thursday, and I installed them this morning. Bought the $14 tool along with it, was an easy install. Can't tell right off hand if anything is running better per se, but at least I have both a new O2 sensor and AF sensor. I thought what the heck and bought a new AF while I was at it.

Still have pinging whilst hitting the gas in top gear, but I'll try to work the bugs out on that one. Thanks for the help!
 

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Good Info. Ordered the Denso models last week from rock auto, and they came n Thursday, and I installed them this morning. Bought the $14 tool along with it, was an easy install. Can't tell right off hand if anything is running better per se, but at least I have both a new O2 sensor and AF sensor. I thought what the heck and bought a new AF while I was at it.

Still have pinging whilst hitting the gas in top gear, but I'll try to work the bugs out on that one. Thanks for the help!
did you clear the codes?

or pull the negative on the battery for half a hour?

this to clean things out and see what reappears?
 

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Discussion Starter · #11 ·
did you clear the codes?

or pull the negative on the battery for half a hour?

this to clean things out and see what reappears?
Eagleeye, yep. I disco'd the negative terminal, and it took me about an hour to install, and then I had breakfast. I actually got into the car to back it off the ramps, and forgot I disconnected the battery...wouldn't start! HA!

I checked my OBD-II app, and the codes were all gone. We'll see how she goes!

Thanks!
 

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Discussion Starter · #12 ·
Just a Quick note and a Thanks to EagleEye!

I replaced BOTH sensors, AF and O2 with Denso units from Rock Auto. Easy swap, spent $15 on the tool since it would be easier than borrowing one from a parts store. (Come to find out, my 2002 Caravan with 178K is hitting me with an O2code just this weekend!).

After one week and 2 days, the check engine light is OFF, and we are OK for now. Praying that it stays that way for a trip across Kansas. Hafta have cruise.

A side note, I did have 87 octane (wife put it in) whilst complaining of pinging. She then put in 89, it mostly went away. I filled up yesterday with 91, and the pinging is pretty much gone. Looks like I might spend roughly $150 this year on peace of mind with premium fuel. It's about a 20 cent difference.

That's my story and I'm sticking to it, no Cat for me now. I also appreciate my local muffler guy telling me that cats wouldn't fix it!

Thanks to the subaruoutback community!!
 

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probably some little fixes to try to get a 2008 2.5 N/A to start taking regular 87 gas without pinging in low elevations.

but so far, so good.
 

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(formerly) 03 H6 OBW , (presently) 06 WRX Sportwagon & 2021 Honda CR-V
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not uncommon for a bad knock sensor to lead to problems, like pinging or poor power - cheap/easy to replace.
 

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Discussion Starter · #15 ·
Well it looks like I never followed up completely on this post...for those of you who are interested.


The O2 sensors seemed to clean things up, and the dealer upgraded the software. So it ran well for a few months, then I have a follow up post where it might have thrown a rod, and it's been in the driveway since April......


Cheers!
 
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