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Work around for 00420 code


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22 replies to this topic

#1 charm

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Posted 12 July 2013 - 08:36 PM

So, I've decided I'm not a fan of the spacer 'fix'...it appears to only put off the inevitable. My cats, aftermarket ones, aren't getting hot enough and are clogging. The mechanic feels this is due to having a rear O2 sensor telling the front O2 sensor that everything is fine even when it's not. Here's my idea for a more permanent fix and what I want to know is, is it less expensive than buying new Subaru cats. I live in a part of WA State that requires emissions testing, but my in-laws don't. Re-registering my car at their address will be easy. It's from this point that the meat of question comes. First, I'd pull the bad cats and swap them with a straight pipe. Where can I get such a thing? Next, and this is my own OCD, I NEED the CEL to not always be on. Is there a way to program the computer to deal with the lack of cats? Is this less expensive then replacing the cats? I have a funny feeling that even without the cats, the car would pass a tailpipe test at the emissions place, but they'd never hook it up! Thoughts on my plan, other than my ridiculous need to not have the CEL always on?

#2 grossgary

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Posted 12 July 2013 - 11:29 PM

have you posted about this before?

 

remove the converters and ream them out, straight pipe with no fitting/work/cost.

someone will know if that causes a CEL or not....surely tons of people have done that before, i've always wondered as well since converters aren't required in my state.

 

new converters would also put off the inevitable...like the current aftemarkets are currently doing from when that decision to replace was made - and it'll come back due to a running condition in the engine that's frying the conveters (if that's really what's happening - that's thrown around far more by mechanics than it actually happens so it's hard to know). 

 

cardoc has a thorough thread on subaruoutback.org that goes through tracknig down the actual cause and not simply throwing one of two band aids at it - the spacer or new converter.

 

that being said, a spacer is by far the better and cheaper band aid.  a converter is an expensive band aid, though it may stick for a long time.



#3 nickb21

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Posted 13 July 2013 - 01:17 AM

What year/model/miles?

 

The rear O2 sensor is only used to check that the cats are working correctly. It does not affect how the computer calculates fuel mix or anything else. (No idea if this is different on 2010+).

 

I agree that you need to figure out the problem first (maybe an issue with wires, plugs, injectors, etc) before getting a solution for the cats. Maybe it's time for a front sensor? Maybe the mechanic just wants to spend your $?

 

You could also buy some used OE cats - I've seen low mileage ones go for less than 100$. Depending on your model/year there could be a good number to choose from (not to mention availability in your area should be wayyy better).

 

I read somewhere about folks running gutted cats and putting a simple diode in-line to trick the ECM. Never tried it myself, but maybe worth a shot, otherwise you might be stuck with the anti-foulers.



#4 grossgary

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Posted 13 July 2013 - 08:50 AM

good quesitons nick, though i think he's probably up on this stuff - mileage and general tune - original front O2 sensor(s)?  plugs, wires, air filter? exhaust leaks?

 

later models do use the rear O2 for additional purposes, but not until 2005 or later.

 

good point i bought an entire OEM exhaust from a western/non-rusty state for $175 minus the header for my 2002 OBW earlier this year.  nice, non-rusty, OEM quality for cheap.



#5 johnceggleston

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Posted 13 July 2013 - 01:19 PM

how old are the replacement cats on the car?

aftermarket cats do not last long.

 

i have heard that a straight pipe / no cats will not throw a code if you use the spacer on the rear o2 sensor.

but i don't know for sure.

 

but since the cats are not working correctly now, and since you have to do something,

pull the cats and ream them out as mentioned.

leave the spacer in.

and see what you get.

 

you may have to install a ''subaru'' front o2 sensor.

this fixes a lot of p0420 codes.

if the front sensor was not replaced when the cats were, or if it it is not a high quality subaru item, it could be the cause of the code.


Edited by johnceggleston, 13 July 2013 - 01:21 PM.


#6 johnceggleston

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Posted 13 July 2013 - 01:26 PM

they are hard to find because the salvage yards cannot sell them, but i would locate and install used subaru cats from some one parting out a car.

this will be a good first step toward fixing your car.



#7 nickb21

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Posted 14 July 2013 - 01:09 PM

they are hard to find because the salvage yards cannot sell them, ...

 

Are you sure? I've seen them listed on car-part under "Exhaust Assembly". Though I wouldn't be surprised if they can't due to the metals or some kinda emissions regulations...



#8 johnceggleston

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Posted 14 July 2013 - 02:07 PM

not 100%, but i'm pretty sure.

i have never tried to buy one.

 

of course i have always thought they could sell an exhaust assembly saying it did not include the cats, but make a mistake.

but i think they gt in pretty big trouble if they get caught.

 

but it could be like the federal law and handicapped ramps.

law says you have to have them, but there is no federal ''police'' force to enforce the law.

some one else has to complain.

and even then they have to get a federal somebody to listen and issue a ''something official''.

usually a law suit is easier to start.

 

call a yard tomorrow and ask.


Edited by johnceggleston, 14 July 2013 - 02:13 PM.


#9 86BRATMAN

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Posted 14 July 2013 - 02:15 PM

Here in Virginia it's illegal to sell a used cat (at least for a salvage yard), it's also illegal for a shop to install used ones. I am not sure if it's federally or locally regulated. But that's the way it is here, if you can find someone who is parting one out and you can do the work yourself you should get subaru cats back on there. What symptoms were presented initially to warrant replacing the cats?

I've never gutted subaru cats, but other makes running obd2 will throw a cel when it's done. I have no reason to believe ours would act any different, so you'd still have to run the spacer if you gutted them.

#10 J A Blazer

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Posted 14 July 2013 - 02:15 PM

I'm tired of the 420 code, and after 170K miles I guess its time to replace the entire exhaust system anyways; there is already one patch in it.  A reputable vendor sells a complete set of necessary parts, made by Walker, for about $650.  Anyone with Walker experience, good or bad?  TIA.



#11 charm

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Posted 15 July 2013 - 09:11 AM

It's a 2000 OBW, 219k miles.

 

There's a bit of saga here.  I bought the car with blown headgaskets and the associated clogged cats at 125k.  Replaced the cats with aftermarket cats from a pretty crappy exhaust shop.  They were bad enough that, 6 months later, when the 420 code came back, I decided it was preferable to spend money then to allow them to touch my car again.  So, on went the 2nd set of cats in 6 months.  The second set, I believe were Walkers...so I would recomend against them.  Use Subaru or don't bother.  The O2 sensors were replaced at that time.  They are both Subaru sensors, but they do have a few miles on them.

 

So, these cats lasted me a few years and about 75k miles, give or take.

 

The O2 sensor is, to quote the mechanic, "lazy." 

 

In other news, the car also has the 2nd set of bad headgaskets since I bought it.  The shop that was supposed to be the best in the Seattle area also appears to have been the last one to jump on the Six Star band wagon.  That left me with a very expensive headgasket job with single layer head gaskets.  I have since switched away from Smart Service as a result.  All Wheel Drive auto, like all businesses, wants my money.  However, they clearly want my money over time and if they don't feel I need something, they may tell me it's coming, but will suggest putting it off.  They are also suggesting clumping things together.  It saves me labor money, for example, to do the headgaskets and timing belt together...and exhaust stuff.

 

I'm going to take the car to a stealership and get a second opinion on the headgaskets.  If they don't feel the headgaskets are dribbling (it may just be the rear plate), I'll find another shop, again.

 

If the headgaskets are having issues, I may very well be stretching the ability of the cats to clean up what I'm throwing at them depending on what the gaskets look like internally.  If that's the case, the cats would be on their way to be clogged as suggested.  The mechanic mentioned that they weren't getting hot enough, although I have no clue how exactly that gets tested.

 

This is all deja vu for me.  It feels like 2008 all over again!  That's why I was asking about a work around.  I'll spend the money if I can get another 5 or so years out of the car, but otherwise, I'm done with it.  This is getting stupid.



#12 grossgary

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Posted 15 July 2013 - 11:03 AM

OH MY.  i thought i recalled discussion about your car previously, what a mess. sounds like you own a german car, you are very resolved to have the car in the shop that often and spending that amount of money.

 

if you're game on to do this again use the EJ25 turbo headgaskets (which don't leak) and resurface the heads.  heck at this point i'd be tempted to tell them to resurface the block for good measure!

 

"this is getting stupid."  - you are a very good person, or polite forum user, or both, to only say that!



#13 charm

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Posted 16 July 2013 - 09:09 AM

Bonus!  I'm due for emissions in August.  This is going to have to happen in the next 5 or 6 weeks before my registration expires. 

 

So, basically, I'm thinking I'll write the check to have it all done or sell the car and take my chances with the reliability of something else.  If I keep it, I keep a known quantity.  If I do the work correctly this time, with the Six Star headgaskets and Subaru cats, and a shop that will use both of those, this money should be better spent. 

 

I wish I had my garage back so I had a place to do this myself.



#14 WoodsWagon

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Posted 16 July 2013 - 11:15 PM

If you are due for emissions and they are thorough, a spacer on the rear 02 sensor won't get past them. It will however work to eliminate the p0420 code. I've seen it work on cars with straight pipes where the cats used to be.

 

p0420 doesn't indicate that the cats are clogged, just that they are failing to adequately burn the exhaust. So there isn't any performance or MPG penalty to a failing cat. If your cats are actually physically clogging and restricting the exhaust, you have bigger problems. Are you dumping in fuel additives to the tank or letting the car sit idling for long periods of time?

 

If the headgaskets are leaking coolant, toss in a bottle of Subaru Coolant Conditioner if it doesn't already have one in the system. If it's leaking oil, how fast? Can you just add a 1/2 quart now and then? Spare oil bottles fit in the handy pocket in the right rear of the cargo area. At 200+k miles, you can justify pouring fluids in to replace leakage rather than fixing the problem.

 

Oh, and subaru dealerships are still installing the single layer headgasket. It's the current spec'd part for those cars, so that's what the parts dept supplies and the tech installs.



#15 brus brother

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Posted 17 July 2013 - 07:04 AM

I  am at the end of 2 years of P0420 and just started a new topic on Logical Analysis of P0420 http://www.ultimates...entual-sticky/.

In the meanwhile, I have passed emmissions two times. I have a $20 OBDII code reader that also clears the code. To reset the systems as ready (required to pass emissions), I then follow a fairly standard procedure of driving a very steady  (no accelerator or brake) 50-55 mph for about 10 minutes then slow to a stop without touching the brakes then accelerate to 55 again. It is best to do with 1/2 tank of gas. Use the code reader again and all systems should now read "ready". Drive slowly to your emmissions center and you should pass.


Edited by brus brother, 17 July 2013 - 08:45 AM.


#16 charm

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Posted 20 July 2013 - 10:35 AM

Thanks Brus, I'm going to need to read your post a few more times.  I come from a background of old cars and I'm still working on learning the car computer language.  A couple more years and I might get it!  ;)

 

Woods, the car has the spacer.  The cats aren't getting hot enough so all the crude sent to them doesn't burn up as it should.  As a result, clogged cats.  The mechanic seems to think, contrary to what I've read here, that the feedback the rear O2 sensor sends to the computer DOES adjust the mixture and creates a richer A/F mix.  Running too rich, over time, would certainly damage the cats if they're not getting hot enough.

 

The head gaskets are showing an external leak, so far, no signs of an internal leak.  We're talking a half quart of oil between oil changes.  I know people that burn more oil then that between oil changes and aren't leaking anything.  This does bring up a good reminder for me...I need to get a second opinion.  If the oil leak is coming from the seperator plate, the engine still needs to be mostly removed, but the heads can stay on the block.  The leak is reportedly coming from the rear of the head so I'd want somebody else to peek at the car and tell me where it's coming from.  I don't think there's a big cost difference between head gaskets and rear seperator plate service so I'm not sure I care that much.

 

The Six Star brand head gaskets, although not installed by the dealer, have done a much better job of providing a long term fix for the head gasket issues then the Subaru ones.  Living in a state where Subaru's represent a large percentage of the cars on the road, Subaru mechanics are abundant.  As of early 2008, most had gone to the Six Stars away from the Subaru ones...except my former mechanic, Smart Service.  They switched a year or so later.  While Subaru is still recomending the Subaru gaskets, people are having much better long term results with the Six Stars.  If they were in my car, there's a good chance that I too would be having better results.



#17 nickb21

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Posted 20 July 2013 - 12:40 PM

Wow, heck of a saga. :/

 

How's your gas mileage? Due to some, uh, rust 'issues', I've been running without my rear O2 for about a month or so. Gas mileage has stayed the same; right around 26mpg mixed driving.

 

Has the mechanic logged/looked at the fuel trim values? I wonder if that info would help out..



#18 charm

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Posted 08 August 2013 - 10:52 PM

The fuel mileage has been slowly declining for awhile.  Strangely, it recently got really good!  I have no idea what that means.

 

The mechanic ran the full diagnostics including fuel trim levels.  For all I know, he took the temp of the cats.  That might be how he knows they're not running hot enough.  He might also know that because the CEL turns off when I drive in the city or over mountain passes but comes back on when I drive 50 mph on country roads with CC set where the engine just doesn't get as warm.

 

I'm seriously debating ditching this car!  With most of the worst case scenario items (warped block not included) the estimate is $4600!  That includes cats, O2 sensors, every engine gasket and the full Monty timing belt service.  Heck, it even includes the replacement for my splash pan!  With a transmission that may not see too many more miles, it's tough to put that kind of money into the car.  Other than all this, it's working great and if I was pretty sure I wou;dn't have to do this again for 200k miles, I wouldn't hesitate.



#19 brus brother

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Posted 09 August 2013 - 06:35 PM

Charm,

I suggest you clear the code (Autel 300 about $20) and drive around as recommended in my earlier post to set the systems as "ready". It's really quite simple. You then can pass emissions and drive on for years to come (put a piece of black tape over the CEL). I like the idea of a car running properly but your's seems intent on torturing you. Save your $ for your next car. Expecting to get another 200K miles is admirable but based on current age and mileage, the car would be 26 years old so, the seats will probably collapse under your butt or the AC will fail or the transmission will fail, or... any number of odds and ends that might give out and make this current investment of $4600 plus ill advised.

Just my 2 cents. ;-)


Edited by brus brother, 09 August 2013 - 10:29 PM.


#20 Fairtax4me

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Posted 10 August 2013 - 05:14 PM

If the cats aren't getting hot enough it's because the exhaust gas mixture is too lean, or the heat shielding on the Y pipe and cats is gone. None of that has anything to do with the rear oxygen sensor. The rear sensor is just a check sensor, it does not affect air/fuel ratio. You can unplug and remove the rear sensor and the car will run exactly the same.

Some reading material on how catalytic converters work: http://autoshop101.com/forms/h64.pdf

On page 5 it talks about the ideal signal from the front oxygen sensor and how that signal is altered when the sensor is fouled or gets old. It becomes "sluggish" or "lazy" because the voltage signal does not swing back and forth as it should.
In comparison to the front sensor, the rear O2 sensor signal should normally swing very slowly, and stay near the middle voltage range of the sensor, about .45v. This indicates a steady amount of oxygen in the exhaust, which would show that the cats are working normally.


Spending $4600 on a car that's worth $4600 is hardly the best investment. I find it hard to believe that the cats are clogged after only 75k miles, but they are aftermarket parts so who knows. Checking for clogged cats is very simple, you just look inside them. But that usually means cutting off rusty bolts and trying to get the rusty flanges clean and flat enough to seal again so they won't leak. A leak in the exhaust at one of the flanges will allow air into the exhaust stream and set the same p0420 code.

#21 J A Blazer

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Posted 11 August 2013 - 05:45 PM

Fairtax: Question regarding your comment about an exhaust leak being a possible cause of a 420. Is that only true if the leak is upstream of the downstream sensor? Thanks.

#22 Fairtax4me

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Posted 11 August 2013 - 08:18 PM

Yes, the leak can be anywhere between the cylinder head flange and the rear sensor.

#23 charm

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Posted 22 September 2013 - 11:32 AM

With my schedule, my only option was to fix the car.  So, it's fixed.  This time, hopefully, it's fixed correctly.

 

Exhaust leaks certainly affect the P0420 code.  I've had to deal with that very thing.  I finally found a good exhaust shop who ended up charging me very little to spend almost an hour under the car seeking out little pinhole exhaust leaks from the first POS exhaust shop that did the work on my car.  I figured out the exhaust leak thing when running some injecter cleaner, I forget the name, through the car.  The smoke that would normally only bellow through the exhaust pipe was also bellowing from under the car!  Made finding the leaks pretty easy.

 

Anyway, now that I've spent stupid money on this car, now I can look forward to replacing a transmission.  Not because there's anything wrong with it right now, but because that's just the way it's going with this car.

 

But, before that happens, I'm going to enjoy, and I really do mean that, fixing the little nuasance issues, like CC, and my non-dimming auto dimming mirror.  Maybe a few dash lights.  Stuff like that...fun stuff.

 

But, my mechanic did a great job.  They did a ton of work.  They were careful not to replace stuff that didn't NEED to be replaced that could be easily replaced later...the splash pan is a great example.  It needs to be replaced at some point, but it's not dire and easy to do later.  Maybe I'll find one at a bone yard at some point.






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