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-   -   catalytic problem (http://legacygt.com/forums/showthread.php?t=201141)

RallyartRob 02-05-2013 07:05 PM

catalytic problem
 
hey guys my 98 legacy gt sedan started to throw a catalytic code its happened twice now takes about 500 or more kms to come on tho when i clear it or remove the battery.

The first time it happened i was going over some pretty bumpy road the second time again there was some bumps. Anyone think it might be a loose O2 wire or most likely just an old cat, the car has about 276000 and had a new exhaust put on in the last year or two not sure if the cats were done tho. And it was e-tested in October 2012 and passed with no problems at all.

Still seems to drive fine and doesn't seem to effect the efficiency or performance at all.

P0420 Catalytic System Efficiency, below threshold c bank 1

I am wondering if u guys know would this be the front smaller "L" shaped cat or the longer straight second cat?

Thanks

spooln30 02-06-2013 08:08 AM

Get a scan tool and check the o2 data. They both should sweep up and down @ idle and at 2500rpm should hold voltage steady. Also the front cat is a pre-cat and the second one is the main. Three causes are, bad or weak o2 sensors, bad cat or a exhaust leak by the cats. A exhaust leak by the cats will cause a false reading thus making the ECU think there's a lack of efficiency thought the cat. GL.

mnstrmech 02-06-2013 08:11 AM

its the front cat. only the front cat is monitored by the O2 sensors. so, gotta get that front cat replaced soon. Id also suggest doing a tune-up with at least fresh plugs, the majority of cats die because people dont maintain their car properly, dont tune it up when they should, which in short, can ruin the cat.

spooln30 02-06-2013 08:13 AM

BTW, the o2's are placed in front and in back of the second cat so that is the one the ECU checks the flow efficiency of. The first pre cat just helps burns so the second cat doesn't have to work as hard. Remember that if you have a cylinder misfire and let it go for a while you will destroy your cats. Same with running too rich, burning oil or coolant for extended periods of time.

Kiyo1990 02-06-2013 08:38 AM

I am having the same issue myself. I was planning on doing headers, new o2 sensors and a front cat anyhow. I just need to get the o2 sensors and good to go. I am pretty sure that your cat is bad, but if you want try for o2 sensors first.

Biggest thing, find out if they put on new cats. If they did I'd check the voltages on the o2 sensors.

spooln30 02-06-2013 08:41 AM

Sorry MNS is correct the front cat is the main. I just took a look at mine. But done rule the cat as the issue just yet check the other problems I listed above first.

mnstrmech 02-06-2013 09:39 AM

actually, being an ASE technician for the last 10 years, a p0420 IS a dead cat, 99.99% of the time. If your downstream O2 sensor is bad, then you get a p0139 B1S2 O2 slow response code pops up.

Osei 02-06-2013 12:10 PM

Quote:

Originally Posted by mnstrmech (Post 4281085)
actually, being an ASE technician for the last 10 years, a p0420 IS a dead cat, 99.99% of the time. ......

I disagree, even though I am not a certified mechanic.
On Subarus at least, 90% of the time it's a bad front O2 sensor and those who frequent this forum who have had this issue can add their own 2 cents.
I personally have had 4 different Subys which have had this code come up and in every case it was resolved with a new front sensor.

Now if you continue to run with it, you may start to burn rich, which will eventually ruin a cat.

O.

mnstrmech 02-06-2013 01:30 PM

Quote:

Originally Posted by Osei (Post 4281421)
I disagree, even though I am not a certified mechanic.
On Subarus at least, 90% of the time it's a bad front O2 sensor and those who frequent this forum who have had this issue can add their own 2 cents.
I personally have had 4 different Subys which have had this code come up and in every case it was resolved with a new front sensor.

Now if you continue to run with it, you may start to burn rich, which will eventually ruin a cat.

O.

thats why i said 99.99 of the time. Thats also in relation to ALL vehicles, not just subaru's

Osei 02-06-2013 01:41 PM

Not to argue, but this is a Subaru forum.

The way that it is worded tends to lean one who is experiencing this type of a problem, to think that their cat needs replacing.
While it may be true in GM, Ford, or BMW world, not here.

O.

johnegg 02-06-2013 03:27 PM

i'm with O.

suabru cats will last the life of the car if you do not damage them by driving with a blinking CEL. of course they can go bad, but they usually do not. but some dealers and some shops love selling new cats when the owner gets a P0420.

replace the front o2 sensor with a subaru or HIGH quality o2 sensor. (cheap sensors may not fix the problem.) you want the front one working really well since it controls the air fuel mixture.

the rear o2 sensor just checks to see if the cats are doing their job. and almost any sensor will work in this position.

but the cats rarely fail in subarus. buying aftermarket cats is a waste of money.

some owners have had their emissions check even when they had a p0420 code, and they passed the test. this means that on some suabrus, even when they have a p0420 code the exhaust emissions are with in federal specs.

do not replace the cats.
it is not the cats.
replace the front o2.

there are lots of things that can cause a p0420 code. the front o2 sensor is the most common. but there are others.

check this out:
http://www.subaruoutback.org/forums/...0420-diag.html


RallyartRob 02-06-2013 05:18 PM

Quote:

Originally Posted by johnegg (Post 4281801)
i'm with O.

suabru cats will last the life of the car if you do not damage them by driving with a blinking CEL. of course they can go bad, but they usually do not. but some dealers and some shops love selling new cats when the owner gets a P0420.

replace the front o2 sensor with a subaru or HIGH quality o2 sensor. (cheap sensors may not fix the problem.) you want the front one working really well since it controls the air fuel mixture.

the rear o2 sensor just checks to see if the cats are doing their job. and almost any sensor will work in this position.

but the cats rarely fail in subarus. buying aftermarket cats is a waste of money.

some owners have had their emissions check even when they had a p0420 code, and they passed the test. this means that on some suabrus, even when they have a p0420 code the exhaust emissions are with in federal specs.

do not replace the cats.
it is not the cats.
replace the front o2.

there are lots of things that can cause a p0420 code. the front o2 sensor is the most common. but there are others.

check this out:
http://www.subaruoutback.org/forums/...youve-had.html

so how would an O2 sensor read a below threshold cat efficiency problem if its infront of the cat? or is there one between the two cats and one after the second?

edit 1: i read through a bunch of the outback forums someone posted and the list goes on, one guys says it could be.....and lists pretty much everything that would throw a code possible...another guy says bad gas, a bunch say front o2, some say rear o2 some say the cat.

alot of people say they put the new gas in and problem solved, im wondering if it could be related to a dirty filter in my case since both times the light did come on was when my tank was low but after i filled up it stayed on so maybe not.

spooln30 02-06-2013 05:43 PM

Being a Toyota certified master tech and ASE Master Tech with 15 years in the biz I can tell you that Japanese and Euro cars have much higher quality cats made from gold and platinum and should never go bad unless someone's drives with a cylinder misfire for a while and a while I'm talking a year. American cars have much cheaper cats being made of mostly rhodium with small amounts of platinum which will fail quite quickly with a cylinder misfire. Like I said above check the o2 data and also for a exhaust leak. They both will cause a P0420. I believe there's 3 o2 sensors on our cars. Also 96 Subaru Legacys with the 2.2 will pass emissions without the monitors being fully reset. I know this because I owned one and couldn't figure out why my cat monitor wouldn't set so I logged in the EPA's website and found a list of OBD2 cars that do the same thing. Check the rest before replacing the cat and I also I wouldn't say all aftermarket cats are junk. Bosal and Magnaflow cats are actually good cats just to name a couple.

johnegg 02-06-2013 06:39 PM

Quote:

so how would an O2 sensor read a below threshold cat efficiency problem if its infront of the cat? or is there one between the two cats and one after the second?
as ypou point out , this is a two sided problem.

the rear sensor actually reports the ''low efficiency'' condition.
but the front sensor, being old and tired even thought it is not yet throwing a code as being bad, is the one controlling the flow INTO the cats, and this is where the problem lies.

history has proven:
you can replace the rear sensor and it usually does not correct the issue.
if you replace the front sensor with a subaru unit, or HIGHER quality, this will usually correct the problem. but not always.

there have been reports of owners replacing both sensors with subaru units and replacing the cats with subaru units and still not clearing the code. this rare but it still has happened.

and there is a work around for this, but i do not recommend it. better to find the cause and fix it.

but with subarus, it is very rarely the factory cats. if the car has aftermarket cats then all bets are off.

regarding the link above, if you concentrate on the posts by the original poster you will learn something. others may agree or disagree and post stories about their experience. but ''cardoc'' knows his stuff and has a lot of good info. read his posts and you will learn a lot about subarus.

HTH

Kiyo1990 02-06-2013 08:16 PM

I do have a question on how Subaru sensors are located. As in, which is sensor location coded?! Which is front o2, rear 02 and last 02? I have the p0420 code and am replacing the o2s, headers and car (due to rusted flange).

Edit: what confuses me in monster...I thought the downstream would be b1s2, being its down stream. Correct? Or is subaru flipped?


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