Dtc P0420 '00obw

[porcupine73]

OK so the MIL/CEL came on the way into work this morning. Read it immediately with the scan gauge - P0420 which I already know is 'catalyst system efficiency below threshold' from other posts on here and alldata. No other codes reported.

 

'00OBW 2.5L N/A AT 107k miles

 

So I cleared it to see if it will come back.

 

1. I'm pretty sure I replaced the rear o2 sensor maybe 15k miles ago but I can't remember if it was on this '00obw or on the '96 so I'll have to check.

 

2. According to my.subaru.com the front o2 sensor was replaced at about 80k miles under recall (some piece could break off or something)

 

3. No noticed difference in performance; actually scan gauge was reporting record mileage for this vehicle today 29.9mpg; usually it's about 28.5 or so.

 

4. Bought premium gasoline last night at a relatively new 'Valero' station where I haven't bought from before.

[nipper]

OK so the MIL/CEL came on the way into work this morning. Read it immediately with the scan gauge - P0420 which I already know is 'catalyst system efficiency below threshold' from other posts on here and alldata. No other codes reported.

 

'00OBW 2.5L N/A AT 107k miles

 

So I cleared it to see if it will come back.

 

1. I'm pretty sure I replaced the rear o2 sensor maybe 15k miles ago but I can't remember if it was on this '00obw or on the '96 so I'll have to check.

 

2. According to my.subaru.com the front o2 sensor was replaced at about 80k miles under recall (some piece could break off or something)

 

3. No noticed difference in performance; actually scan gauge was reporting record mileage for this vehicle today 29.9mpg; usually it's about 28.5 or so.

 

4. Bought premium gasoline last night at a relatively new 'Valero' station where I haven't bought from before.

 

Well sure make it difficult.

 

SO lets confirm, the car has a subaru brand o2 sensor in it. DOuble check what the recall was for exactly.

Il'd say let it fgo for now, though even bad gas wont throw off an o2 sensor.

It is possible that the second o2 sensor is tired (either one can give that code)

 

Let us know if it happens again.

 

nipper

[Suzam]

I Agree with Nipper.

 

I have a MY95 Legacy that throws that code every 6-12 months. If I reset it, I can go for another 6-12 months before the CEL comes back on. No difference in performance or gas milage, however it has over 150K miles on it, so I guess I could replace the O2 sensor........ **Yawn**....... just too lazy.

zzz

[porcupine73]

Thanks for the help guys. The recall front o2 sensor replacement (WXW-80) was done at 77,821 miles on 11/15/03 (prior to my buying the car used).

 

I'll double check tonight to see if I already replaced the rear o2 sensor on this vehicle (or if it was on the '96); if not I'll put it in (OE).

 

Cleared the code, will see if it comes back, wow the scangauge is so handy for that since you can just press the button and read and clear the code immediately without even pulling over.

 

The front o2 sensor recall replacement was:

Recall - O2 Sensor Replacement

NUMBER: WXW-80

DATE: 01/2001

 

APPLICABILITY:2000MY Subaru Legacy and Outback 4EAT

2000MY Impreza 2.5 RS MT5 or 4EAT

2000/2001 MY Forester MT5 or 4EAT

 

SUBJECT:

Front Oxygen (Air/Fuel Ratio) Sensor

 

Subaru of America, Inc. (SOA) has determined that the affected vehicles listed below may experience front oxygen Air/Fuel (A/F) sensor element cracking. Should this occur prior to replacement, the CHECK ENGINE warning light/Malfunction Indicator Lamp (MIL) will illuminate steadily while the engine is running advising the driver of a malfunction and the need to seek repair service.

 

This program will involve replacement of the front oxygen (A/F) sensor on affected vehicles.

 

Please Note : Because of the number of affected vehicles and part availability, this program will be released in phases determined by geographic location. Dealers will be notified of the release schedule when available.

 

AFFECTED VEHICLES

 

^ 2000MY Subaru Legacy and Outback with 4EAT only

^ 2000MY Impreza 2.5 RS with MT5 or 4EAT

^ 2000/2001 MY Forester with MT5 or 4EAT

[porcupine73]

I checked and I did replace the rear o2 sensor about 10k miles ago. I made about 4 'trips' since resetting the light yesterday and the light hasn't come back on. Anyway, the vehicle seems to running exceptionially smoothly and powerfully since that light has come on and with better mileage, maybe that Valero gas is better than what I was buying previously.

[mtsmiths]

Our O2 sensor has been replaced twice under the TSB by Subaru. After clearing codes for four years on our '00 Legaback, and never experiencing any driving problems I gave up and performed the Click & Clack fix.

 

A 3/4" dot of black vinyl tape. :-\

[nipper]

Our O2 sensor has been replaced twice under the TSB by Subaru. After clearing codes for four years on our '00 Legaback, and never experiencing any driving problems I gave up and performed the Click & Clack fix.

 

A 3/4" dot of black vinyl tape. :-\

 

except for those of us who have emission inspections. Black tape isnt a good idea, as it can hide other important reasons the check engine light comes ons.

ALso cats do go bad, just no where near as often as they used too

 

 

nipper

[porcupine73]

Yep, I have to pass a NY emissions test, not the Westchester one, but all the readiness monitors must be set and the CEL/MIL can't be on. Fortunately my current inspection is good for about 10 more months.

[johnceggleston]

Yep, I have to pass a NY emissions test, not the Westchester one, but all the readiness monitors must be set and the CEL/MIL can't be on. Fortunately my current inspection is good for about 10 more months.

 

the bad news, 10 months is nothing in the life of a subaru. you better start ....

[porcupine73]

Yes the Suby's last a long time don't they! I mean I have 10 months to see if this issue recurs every few weeks or whatever and try a few things to stop it or at least hope it doesn't pop right before the inspection. It hasn't come back yet. If I had to go for inspection next week I'd be more worried since I'd have to time to work with it.

[Skip]

Hey porc,

Please do tell some details about the scan meter system you use.

I have been in the market and like the sound of yours.

Name/brand/cost/available from.

 

Thanks

[porcupine73]

Hi skip, it's the Scan Gauge, you can get it here $165; (I think they're the manufacturer but I can't remember; maybe it's less elsewhere). If you look on eBay you might find it, just verify which model it is as I think there is an older one and this newer one.

 

I really love it and you can display four parameters at once in 'gauge' mode, like intake air temp, water temp, MAF or MAP, voltage, rpm, speed, ignition advance, throttle position, engine load %, and I"m sure I'm forgetting a few.

 

You set it up with your engine size, etc., and it computes mpg (fairly accurately) while driving and gives trip/day/tank averages, etc.

 

Nipper has the newer model; I have the older model.

 

Just one note about it for Subaru's (in case you get one) - certain model Subaru's you have to set this option in there for 'supported' parameters instead of 'all' parameters or it won't display any values.

[johnceggleston]

Hi skip, it's the Scan Gauge, you can get it here $165; (I think they're the manufacturer but I can't remember; maybe it's less elsewhere).

 

how about a group, bulk buy. see if we can get a wholes price>

[erikm]

I am in a similar state with a 2000 Forester 135k miles. CEL P0420. Changed both O2 sensors about 30k miles ago. This actually fixed an issue where I could not drive the car at all because of stalling. Had my exhaust manifold welded where it was cracked about 5k miles ago. Still getting CEL P0420, could the CAT actually be bad, or could the sensors have fried while exposed to a cracked exhaust header?

[nipper]

I am in a similar state with a 2000 Forester 135k miles. CEL P0420. Changed both O2 sensors about 30k miles ago. This actually fixed an issue where I could not drive the car at all because of stalling. Had my exhaust manifold welded where it was cracked about 5k miles ago. Still getting CEL P0420, could the CAT actually be bad, or could the sensors have fried while exposed to a cracked exhaust header?

 

 

Its always bad that the cat is actually bad. It's rare at that mileag but it happens. When you hit your hand against the (cold) cat does it rattle? A bad o2 sensor or two can cause the car to run rich and burn up the cat. How long did you drive with a bad o2 sensor?

 

nipper

[porcupine73]

I haven't got my P0420 code back yet, but this morning I thought I heard a bit of an exhaust leak, and by the time I got to work, wow, it sounds like something is wide open down there. So maybe it's rusted out I'll have to look but maybe it was leaking a little before that maybe that's why I got the code. I think the really deep snow yesterday might have worked the weak point loose.

[ferret]

My own experiences with this code across many different vehicles ( not only Subarus ):

 

1. Look for exhaust leaks anywhere from the engine to the rear oxygen sensor. Many times I have found this to be the biggest cause.

 

2. Failed or failing Catalytic converter. Owners usually don't want to hear this, but unless there is a leak, or slow responding oxygen sensor ( front or rear ), the code is correct when it is set. If you reset this code without fixing anything, it will usually come back in a day...2.....week....next 2 weeks....The converter should be replaced.

 

3. Cheaper than the converter but usually not the cause, replacing the front, rear or both oxygen sensors. Without a code pointing directly at the sensor, or charting the sensor to prove it has a slow response, this is cheaper than replacing the converter, but in most of my experiences, it just puts off replacing the converter.

 

I have seen converters last years and 150K + miles. But it seems the ones that were part of the 99 and newer vehicles are of a different substrate and don't seem to last as long. Somewhere in this time, car manufacturers had to lower emissions again and introduced a slightly different converter and oxygen sensors. Both don't appear to be a long lasting as in the past.

 

My own experiences....and $.02. Take it for what it's worth. You are welcome to input with your own.

[nipper]

I have seen converters last years and 150K + miles. But it seems the ones that were part of the 99 and newer vehicles are of a different substrate and don't seem to last as long. Somewhere in this time, car manufacturers had to lower emissions again and introduced a slightly different converter and oxygen sensors. Both don't appear to be a long lasting as in the past.

 

.

 

They started phasing out platnum in the cat and used something differnt to get lower emissions. I think this has a lot to do with the shorter life.

 

nipper

[erikm]

Its always bad that the cat is actually bad. It's rare at that mileag but it happens. When you hit your hand against the (cold) cat does it rattle? A bad o2 sensor or two can cause the car to run rich and burn up the cat. How long did you drive with a bad o2 sensor?

 

nipper

 

Less than a week, and at the time the codes pointed to both o2 sensors. I could not get to work, so it was an easy decision. I drove with a cracked header for quite a while. The shop said that by hitting the header with the welding torch, they could see the temp difference where the cracks were and fixed them all. That noise is gone, too. Will check the cat for rattle. Other than emissions problems, what is harm with bad cat?

[Wayne Boncyk]

Depends on how the cat is failing. If it is just covered with crud from oil or coolant contamination in the exhaust, it sometimes will simply get a little too hot, and not do an effective job of reducing emissions. Other times, depending on how much crud is in there and how much of the catalyst is still exposed, it will get a LOT hot. That will potentially melt down the catalyst bed, which can then plug the exhaust. Not good for the engine when that happens... but you'll know it in a very short while!

[erikm]

Depends on how the cat is failing. If it is just covered with crud from oil or coolant contamination in the exhaust, it sometimes will simply get a little too hot, and not do an effective job of reducing emissions. Other times, depending on how much crud is in there and how much of the catalyst is still exposed, it will get a LOT hot. That will potentially melt down the catalyst bed, which can then plug the exhaust. Not good for the engine when that happens... but you'll know it in a very short while!

 

Thanks for the paranoia.

 

There is an exhaust shop near me that will normally help people in my situation, but they said that on a Subaru they cannot due to the dual cat thing. If emissions is not an issue to the government, can you drop the cat? How bad is that for the car and/or Earth?

[Wayne Boncyk]

Thanks for the paranoia.

 

There is an exhaust shop near me that will normally help people in my situation, but they said that on a Subaru they cannot due to the dual cat thing. If emissions is not an issue to the government, can you drop the cat? How bad is that for the car and/or Earth?

Technically, every car ever produced with a cat must continue to have a cat for the life of the car... federal EPA regulation. However, if you live in a state where cats are not required to be inspected, what you do in the privacy of your own garage is entirely up to you. Just remember that the OBD-II will set a MIL light when O2 sensors and/or cats are removed from an exhaust system. Additionally, although the engine will still run (and you'll probably notice little or no difference in performance or mileage), you'll technically be running "open loop," where the rest of the emission systems will be not working according to spec.

 

Probably not a big impact on the life of the engine, but you'll be doing your part to add to the CO and NOx components of the earth's atmosphere. If you live in a major metro area (where photochemical smog is a problem), then you'll be doing more than your share of contributing to the "brown cloud." Effects on global warming are more open to debate.

 

You can get aftermarket cats significantly cheaper than those supplied as Subaru OEM, but they usually don't last as long (less catalyst in the bed = fewer operating miles before failure).