97 Legacy Code 0420 Cat Conveter

[eppoh]

My 97 Legacy L w/2.2 CEL came on and has a code 0420. I think this is for catalytic converter. Question is, if so, which one? Aren't there two cats on these cars? How do you know which one is bad?

Edited January 9, 2010 by eppoh

[eppoh]

c'mon, nobody here ever had a catalytic converter issue on a Legacy?

[ScottG]

Not sure if yours has 2 cats. I know it has two 02 sensors. The second one(rear) checks the efficiency of the converter.

 

There are a number of board members who have had this same problem (CEL for inefficient converter) Some folks have spent big bucks at the dealer to have two new O2 sensors and a new converter installed......only to get the same code a year or 2 later.

 

Use the search box to research the threads on ctatalytic converters & the code you found. You'll find a interesting debate & discussion. Some board members have used spark plug anti foulers to remove the rear 02 sensor back fom the main stram of exhaust. This seems to solve the problem of a frequent CEL, but if you live in an area where pollution inspections are conducted, they may not pass it with anti foulers.

 

ScottG

[EVOthis]

Hmmm..Is your cat. convertor assembly one piece or two piece? Some of the early ones had the two cats bolted together...Either way from my experience its usually the front cat. that goes bad...Contrary to what many people say "a bad o2 sensor could throw this code"..in the dozens of the Subaru cat. conv. I have replaced not one of them has come back for the infamous 420 code which obviously rules out a bad sensor...It is much much more likely that if you have a malfunctioning sensor the ECU would throw a code for that....

[idosubaru]

c'mon, nobody here ever had a catalytic converter issue on a Legacy?

yes, but "c'mon - you didn't search?":lol:

 

lots of P0420 threads here and on subaruoutback.org.

[eppoh]

yes, but "c'mon - you didn't search?":lol:

 

lots of P0420 threads here and on subaruoutback.org.

 

 

But c'mon I did search and found no discussions out of 25 that distinguished between front and rear cats. I guess you ASSumed I didn't search.

Not helpful, and if I need a lecture- I'll bug my wife.

[johnceggleston]

i'm on here a lot and i don't remember any discussions about front vs. rear cat. most 420 threads focus on front vs. rear o2 sensor.

 

there is a thread with the anti fouler fix which will eliminate, a lot of the time, the p0420 code regardless of the condition of the cats.

 

 

i know this isn't what you asked for but i thought you might find it interesting.

 

http://www.ultimatesubaru.org/forum/showthread.php?t=107476&highlight=anti*

Edited January 10, 2010 by johnceggleston

[idosubaru]

But c'mon I did search and found no discussions out of 25 that distinguished between front and rear cats. I guess you ASSumed I didn't search.

Not helpful, and if I need a lecture- I'll bug my wife.

 

the attitude isn't helping you. no wonder your wife lectures you! you might like NASIOC better than here.

 

do you know for sure this is a bad converter? the P0420 code can be caused by other things and a lot of folks don't know that or look into it. so that's why we were trying to help by pointing you elsewhere.

 

there's also a way to fix this for $10 almost regardless of what the cause is as well. JCE referenced it above.

 

i *believe* that it's typical for the rear converter to cause more issues than the front, but my experience is limited so whether it's anecdotal or not i don't know.

[eppoh]

the attitude isn't helping you. no wonder your wife lectures you! you might like NASIOC better than here.

 

do you know for sure this is a bad converter? the P0420 code can be caused by other things and a lot of folks don't know that or look into it. so that's why we were trying to help by pointing you elsewhere.

 

there's also a way to fix this for $10 almost regardless of what the cause is as well. JCE referenced it above.

 

i *believe* that it's typical for the rear converter to cause more issues than the front, but my experience is limited so whether it's anecdotal or not i don't know.

 

If I knew for sure it was a bad cat, I'd just buy one and put it on without bothering you.

If one of the cats is clogged, the 10dollars anti-fouler fix, won't fix anything other than putting out the light. I would like to really fix the problem. I guess you assumed I did not know about the anti-fouler jury rig either.

 

The factory manual says start by pulling the rear cat and checking it for damage, then progress to the front.

 

I was hoping to find someone on here who has actual experience with this same problem themselves, willing to offer the advice of their own experience.

 

So if there is someone who has gone through this themselves and willing to share, please feel welcome.

 

Anyone else with presumptuous and pejorative lectures, please feel welcome to piss off and find someone else with an 8th grade character to converse with.

[idosubaru]

subaru has a very detailed process for doing what you're saying but it involves interfacing with the electronics - someone has detailed that in depth and quantitative process here or on subaruoutback.org, i'm not sure which but i've read it.. i've never heard of someone doing it themselves.

 

the more information you can give the better or we have to assume things and start from the beginning. this board is comprised of all sorts of individuals, we have no idea of knowing what you've done, know, or don't know. might save your anger, blood pressure, and need to validate yourself over the interweb by "telling people off".

Edited January 11, 2010 by grossgary

[nipper]

Gary with his attitude, i would just let hime spend the 850.00 ffor that cats and find out that wont fix his problem.

 

i also wouldnt tell him to use a search to find the 100's of discussions on cats and O2 sensors.

 

I also wouldnt tell him that the 420 code 99% of the time refers to a tired Front O2 sensor which needs to be OE. I also wouldnt tell him that there is a second O2 sensor behind the cat that can be replaced with a generic aftermarket sensor.

 

 

Nosirreebob i wouldnt tell him a blasted thing.

 

 

nipper

[eppoh]

 

i also wouldnt tell him to use a search to find the 100's of discussions on cats and O2 sensors.

 

 

I also wouldnt tell him that the 420 code 99% of the time refers to a tired Front O2 sensor which needs to be OE.

 

 

 

nipper

 

So, nipper, did replacing the front sensor fix the problem for you? Were you able to isolate the front sensor by checking resistance as it warmed up? If so, what values were you looking for?

 

My search of the "100's of discussions- before I posted btw, revealed 90% of the posts were people talking about something they heard and had not actually done themselves.

 

I always us OE or OEM for ignition, fuel and emissions parts. Learned the hard way on wife's Toyota over the years.

[idosubaru]

So, nipper, did replacing the front sensor fix the problem for you?

yes he replaced both. like lots of other people have, but i've never heard of anyone testing one.

 

i think most folks figure that at 10+ years old and if they're expecting more miles out of the car, having a new front O2 sensor doesn't hurt and probably pays for itself. my rationale is i'm keeping my 02 OBW for another 100,000 miles, it's going to need new front sensors at some point so i just replaced them now and maximize my return for the investment.

 

the 0420 code is just about the most annoying code you can get from a diagnostic stand point.

a bit of effort and mind juices reveals these:

 

here's the subaruoutback.org thread metioning Subaru's 1 hour test:

http://www.subaruoutback.org/forums/showthread.php?s=&threadid=16769&perpage=20&highlight=0420&pagenumber=2

 

here's some good info on quantifying 0420 codes:

http://www.troublecodes.net/articles/catfailure/

[nipper]

yes he replaced both. like lots of other people have, but i've never heard of anyone testing one.

 

i think most folks figure that at 10+ years old and if they're expecting more miles out of the car, having a new front O2 sensor doesn't hurt and probably pays for itself. my rationale is i'm keeping my 02 OBW for another 100,000 miles, it's going to need new front sensors at some point so i just replaced them now and maximize my return for the investment.

 

the 0420 code is just about the most annoying code you can get from a diagnostic stand point.

a bit of effort and mind juices reveals these:

 

here's the subaruoutback.org thread metioning Subaru's 1 hour test:

http://www.subaruoutback.org/forums/showthread.php?s=&threadid=16769&perpage=20&highlight=0420&pagenumber=2

 

here's some good info on quantifying 0420 codes:

http://www.troublecodes.net/articles/catfailure/

 

But i wasn't going to tell him that.

 

If the O2 senser is over 80K it can be due, and the farther away from that number the more likely it is.

 

You can do all sorts of testing, but when it is obvious it is what it is, then just replace it.

 

 

nipper

[eppoh]

Thanks,

 

I have had the car only a year and don't know how old or how many miles are on the sensors.

 

I will check out the link-looks promising

[mdjdc]

I too had this problem and went to my local subaru dealer. The lead tech told me that the problem would just come back if I replaced the front cat and he was right. I replaced the front cat and both O2 sensors and the problem was back within three months. here in VA it doesn't matter if the CEL is on at inspection, so I just let it go. I did use an aftermarket cat and he had warned me not to do that. I, personally, would not spend the money on new cats unless the car was showing definite signs of being clogged. The code you are getting is for a catalytic cnoverter inefficiency not failure. That means it just isn't scrubbing as well as it should. I would go the route of changing the O2 sensors and see what happens. After that I would do the anti fouler job.