Subaru Outback Forums banner
1 - 17 of 17 Posts

Registered
2007 Outback Basic, 2.5L, 5-spd
Joined
13 Posts
Discussion Starter · #1 ·
Hey all,

So my wife and I bought an '07 Outback Basic back in January, used with about 130k miles on it. MIL came on around 6 weeks ago with a P0420 code. Been doing a lot of googling/reading about P0420 codes lately- I've had several conversations with different mechanics around town, some helpful and some not, but someone suggested that since the only code was the P0420 that it was likely a bad cat con, rather than another issue that would have likely triggered additional codes. Eventually decided after much deliberation, and taking it to another shop and finding out that it already had a direct fit converter, thereby ruling out the possibility of buying a cheaper universal one and paying a muffler shop to install it, to try and change it myself. Got an Eastern Catalytic direct fit that finally came in the mail the other day, only to find that all of a sudden the MIL is out and cruise control works again. I don't want to necessarily assume that the problem is gone, but I'd just as soon not mess with things that aren't broken if that's the case. Any ideas why it may have turned itself off or other experience seeing this happen? Thanks for any thoughts you may have.
 

On the Super Mod Squad
2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
Joined
27,898 Posts
you type MIL instead of check engine light, as if you are use to discussing Chevrolet.

did any of the shops discuss any of the cheaper options,...like a new rear o2 sensor,


or did they just discuss swapping one expensive cat for another.

(this thread gets written like every day here,... p0420, swapping cats first, cheaper more underlying problems reappear, giving the same p0420 code,....)

on my own H4 car: 111,000 miles rear o2 sensor changed at 65,000 miles and again at 100,000 miles ....denso brand which is possibly what subaru relabels. ($75 or so for my car,...bought off amazon, rockauto similar priced).

and take your time sorting it out, ...p0420 by itself is a mild nag code, cancel it and go on with your life if you need to kick the can down the road, it does not hurt anything.
 

Registered
2007 Outback Basic, 2.5L, 5-spd
Joined
13 Posts
Discussion Starter · #3 ·
Oh I just thought MIL was another generic term for CEL...

Guy at O'Reilly's said that he often finds those codes are caused by o2 sensors rather than cat cons. Professional mechanic said it's definitely a cat con. I figured I'd go with the mechanic, with all due respect to auto parts store employees, many of whom I have no doubt are incredibly experienced. From what I've read, it definitely seems like there could be all kinds of different little things contributing to the problem but the two different shops that I talked to (one of which I've gone to before for another unrelated issue and got great service) were just gonna change out the cat without doing any further diagnostics.

What I'm most curious about is why the CEL turned itself off all of a sudden without being cleared. I'd rather fix a problem now than let it go and potentially have a more serious/costly problem later, but I guess I'm wondering what the likelihood is that it's still a problem.
 

On the Super Mod Squad
2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
Joined
27,898 Posts
Oh I just thought MIL was another generic term for CEL...

Guy at O'Reilly's said that he often finds those codes are caused by o2 sensors rather than cat cons. Professional mechanic said it's definitely a cat con. I figured I'd go with the mechanic, with all due respect to auto parts store employees, many of whom I have no doubt are incredibly experienced. From what I've read, it definitely seems like there could be all kinds of different little things contributing to the problem but the two different shops that I talked to (one of which I've gone to before for another unrelated issue and got great service) were just gonna change out the cat without doing any further diagnostics.

What I'm most curious about is why the CEL turned itself off all of a sudden without being cleared. I'd rather fix a problem now than let it go and potentially have a more serious/costly problem later, but I guess I'm wondering what the likelihood is that it's still a problem.
3 drive cycles, is as long as that code lasts in the ECU, if the condition does not present itself again it will cancel itself. last time I had a bout of p0420 the light would come on from on a specific piece of road, (something about my driving habits of those particular days), and it would cancel itself if I did not cancel it just to turn the light out.

many subaru dealers, and those trained by them, want to change the cat first, then sort out the milder cheaper alternatives later....it is easy to make money selling new expensive cats, and then turn around and recycle the platinum in the old cat.

and even for a honest mechanic,...lots a junk material out there to draw off of, to say "change that cat(s)", my own mechanic looking at such junk material on the internet at the time, bought a walker cat for my H4 car, tried it got the p0420 back, and then put the original cat back on, and then tried a new denso rear sensor, (he had just sold me the car at 65,000 miles used by another customer. (he did not bill me for the walker cat, and put the walker one in storage).

in the end it is rumored he even put a spacer on the rear sensor to make it receive less exhaust gas in general, (but I don't know that for a fact.... and avoid looking under there to verify :cool: )
 

Registered
2007 Outback Basic, 2.5L, 5-spd
Joined
13 Posts
Discussion Starter · #5 ·
Ahhh. That makes sense! must be that the rear o2 sensor is happy with what it's seeing now and the code just cleared after a few drive cycles. Sounds like I can probably return the converter I just bought then.

Yeah it really seemed like the way to do it right and do it once would be to run some diagnostics to see if it was a sensor or some other issue instead of just assuming the converter... but as you said, there are some obvious incentives to do so. Thanks so much for your help!
 

On the Super Mod Squad
2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
Joined
27,898 Posts
there are other things,

but it seems logical to start with the source of what makes the code, and at least make sure it is a good looking thing before buying new parts,..

those things get corroded in though so you can damage the existing one getting it out if its been in there a long long time,

________

swapping out an original front o2 sensor, I was happy I took mine to a friend with a lift, as he had to chop it in half with a saw-zal and then as a last resort use a torch to get it out. 100,000 some odd miles over 13 years with salted sand winters.

________

I am thinking we need a sticky thread about how to process and fix p0420 code.

We have lots of little one time threads, land a few long long long discussion threads of the subject, but no quick and easy thing.

like answer yourself these questions 3 if its the otherside ye seeks,...before crossing the bridge of death and buying a cat to replace a good cat..

 

On the Super Mod Squad
2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
Joined
27,898 Posts
I was thinking about something that is not 125 pages long, but one page long. and then locked up.

something for just that code on a otherwise good running car,...and not that code with a bunch of other more nasty codes and the p0420 is just the last incidental one.




1) do you have a exhaust leak between the engine and the last o2 sensor.?

2) how old in years / miles is the last o2 sensor?

3) is your car burning a whole lot of oil?

4) has some fool told you you "have" to buy a new cat or the car will explode? :frown2:
(edit: without even looking at the car).
 

Registered
OBW H6 VDC, Tribeca, XT6
Joined
12,386 Posts
What I'm most curious about is why the CEL turned itself off all of a sudden without being cleared.
That's what they always do, very normal. I've seen them go off for no reason after like 3 years of being on forever.

I'd rather fix a problem now than let it go and potentially have a more serious/costly problem later, but I guess I'm wondering what the likelihood is that it's still a problem.
Depends on your definition of "problem".

You can drive the vehicle indefinitely, 300,000 miles with the P0420 code on with no issues.

Just be sure to do tune ups and maintenance if gas mileage/performance tanks - those things might cause issues.

If you live in an emissions/inspection area - just clear it before getting it tested but long enough to populate necessary digital tables.

If you're interested in fixing it - yeah a new converter will probably fix it, at least temporarily. Until it's performance degrades again and causes more issues...why may or may not happen.

What I'd do:

1. ignore it
2. repair any exhaust leaks
3. get all the tune up stuff caught up - plugs, wires, air filter, PCV valve
4. seafoam the intake and MMO the gas

I someties replace the O2 sensors as preventative maintenance, if it's a great vehicle I'm expecting 250,000+ miles out of. I figure over 300,000 miles, that's far too long to expect an O2 sensor to last. So I might as well just replace them around 150k as preventative maintenance and hope some of that cost is recouped via catalytic converter health and a higher average gas mileage over those 300,000 miles.
 

Registered
2007 Outback Basic, 2.5L, 5-spd
Joined
13 Posts
Discussion Starter · #10 ·
Sorry for the delay and thanks for all the new replies- you've all been super helpful!

Interestingly enough, CEL came back on again yesterday and sure enough, it's my favorite code back to haunt me. It definitely sounds like it's far from a sure fix to swap out the cat, and it's driving fine in the meantime, so I'm gonna go ahead and return it anyway and do a little legwork to actually figure out what may be causing the problem. Speaking of legwork, with the CEL back on I sure do miss my cruise control.... But what can ya do? :) Definitely gonna look into potential exhaust leaks/health of o2 sensors which I have no reason to believe are anything but original and now 130k miles in. Thanks again everyone!
 

Registered
2002 Subaru Legacy Outback 4S3BH665527620828
Joined
998 Posts
That's what they always do, very normal. I've seen them go off for no reason after like 3 years of being on forever.

Depends on your definition of "problem".

You can drive the vehicle indefinitely, 300,000 miles with the P0420 code on with no issues.

Just be sure to do tune ups and maintenance if gas mileage/performance tanks - those things might cause issues.

If you live in an emissions/inspection area - just clear it before getting it tested but long enough to populate necessary digital tables.

If you're interested in fixing it - yeah a new converter will probably fix it, at least temporarily. Until it's performance degrades again and causes more issues...why may or may not happen.

What I'd do:

1. ignore it
2. repair any exhaust leaks
3. get all the tune up stuff caught up - plugs, wires, air filter, PCV valve
4. seafoam the intake and MMO the gas

I someties replace the O2 sensors as preventative maintenance, if it's a great vehicle I'm expecting 250,000+ miles out of. I figure over 300,000 miles, that's far too long to expect an O2 sensor to last. So I might as well just replace them around 150k as preventative maintenance and hope some of that cost is recouped via catalytic converter health and a higher average gas mileage over those 300,000 miles.
I like your post.

Presently figuring out exactly what turns it on on my 2002 H4..
 

Registered
2021 Touring XT Abyss Blue Pearl
Joined
726 Posts
I drove my stoned Honda Insight and current old Civic and didn't worry about it. Too many stories of complete exhaust replacements not fixing anything. Fortunate not to have vehicle inspections in this state.
 

Registered
2005 Outback Wagon 3.0 L.L. Bean
Joined
1,669 Posts
To avoid having to start a thread..."I just replaced my O2 sensor and code came back", Only use Denso O2 sensors.
 

Premium Member
01 VDC, 05 R Sedan, 06 BAJA EJ257
Joined
18,084 Posts
Hate to bump an older thread but.. Would it be the same here like this for a 2002 H4? Same car, Outback...
Its not always a catalytic converter. You have to find out why the efficiency is down and it goes to the engine performance.

 
1 - 17 of 17 Posts
Top