2000 Subaru Impreza Outback 2.2L P0420 Code

Hello everyone! Here's my story and I'm sticking to it, including what I've done, and what I intend to do. Let me know if you have any comments or questions. I'll keep you posted.

The CEL came on at around 90K miles. I plugged in the computer and got the bad news...P0420...catalyst efficiency low. There were no other codes (never have been) and the car was/is running fine...gets 28 MPG. I was also a bit surprised and suspicious to see the cat gone bad so soon, especially in a perfectly good running engine with no issues, no abuses, and no after market tuner junk.

Since I know how OBD-II works I knew the front and rear sensors supplied the info to trip this code, so I went after the sensors first...way cheaper than a new cat. First a new front sensor...no fix, then a new rear sensor...no fix, then a new Eastern Catalytic converter...no fix.

Ok, now I am starting to get frustrated...well OK, just plain pi$$ed! Checked lots of forums, including this one. Saw lots of P0420 issues with Subarus, read lots of talk about ECM reflashes, and stories of folks like me replacing cats (including OEM and aftermarket) and sensors and still getting the code...for no good reason. Sounds to me like Subie has a problem in this area...including TSBs on certain VINs but that's a little fuzzy. Eastern Catalyic was very helpful and said they would replace the cat but I don't think it's bad...I think the Subaru ECM is the problem...it's giving out "false positives"...poor design tolerances.

So, being: 1) cheap, 2) an experienced mechanic, 3) an experimenter, 4) a master cobbler, and 5) someone who likes to "beat the system" whenever possible (in this case I'm trying to beat the bogus Subie P0420 fault identification software) I bought one of those "bung extenders" on Ebay for $10 + shipping.

Sounds like it isolates the rear 02 sensor from the main exhaust flow, thereby reducing signal fluctuations, and tricking the computer into saying everything is OK (which of course it IS!) I say: PERFECT!

I'll let ya'll know if it works. If it does, my only regret will be not slapping one in from the get go. If it doesn't work, well, maybe another new cat? Or go to the dealer and see about the ECM reflash? (and pay waaay to much to fix something that is a design falw that Subie should fix for free).

Lemme know what ya think,

Yeh, I guess it's ILLEGAL!

Reality is: a) my cat isn't bad, b) I'm not polluting and c) it ought to be illegal to design systems that don't work, stick us with problems, and expect us to pay for latent defects! Based on the preponderance of Subie P0420 problems, I must say, this system aint workin' and this may just fix it!

Cheers!

Tele

even if they should flash it for free for what ever reason wouldn't you rather go with that as a cheaper fix then all the other parts and labour?

IMO you're reading a little too much into it. In all that reading about o420s, did you read anything about aftermarket cat. issues? Often on some finiky vehicles, an OE converter must be used because the threshold for error on some makes are very tight and very strict. Lots of aftermarket converters skimp on the costly metal content that makes a catalyst work. So, go back to OE converter and Im sure your problem will be solved.

Darkrooms...perhaps you are correct. I wonder, however, why the original stock cat went out with less than 100K miles on a perfecty good running engine? Maybe it wasn't really bad either. Any experience in this area?

Parts go bad. There's nothing else to it. You think you're the first poster with a 0420 that won't go out after cat replacement? Do you have any idea how many people have asked us that question thinking their situation was unique? Comp will probably post after me how many times he's seen it, MM how many times have you seen it? I've only been here a little over a year and I've seen it at least two dozen times and that's a conservative estimate. It's always the same thing. Poor quality aftermarket cat.
So, yeah, I guess you could say we have a little experience in that area.
Instead of complaining, be happy you got 100K out of your Soob's cat.

Darkrooms, I've seen it enough times to agree with you.

100K on a cat is more of a "ballpark" milestone...some go bad before and some after.

It all depends on how the vehicle is normally driven (short in-town trips vs long highway trips),
the type and quality of fuel, etc.

Looking at the LTFTs may provide some insight, also a dirty MAF, throttle body, etc. can contribute to it as well.

Just because there are no other codes and the engine sounds like it is perfectly running, it ain't always so...maybe running not bad enough to throw a code.

Why not just get the OE cat and get it flashed?

Don't you guys know the oe and the dealer are bad! I mean they are the crooks that built it and sold it to someone right! how dare they! Those guys at the zone have got it all together, you can trust them to be get the right part for the right price all the time. Why return to the dealer to get a reflash that they'd try to charge you for that may keep the light out when you can take old parts off that may still be good and replace them with lower quality new stuff all in the name of diagnosis. I mean it was probably bad anyway right so why flash it and hope when you can get some use out of all those nice craftsman tools most diy ers have. And that's not a crack on Craftsman tools. I love them!

OK, sounds like the general opinion is that the Eastern Cat converter is a POS!

Some comments:

Jeff: you must work for a dealer! Some thoughts on that...I grew up in a garage and been fixing cars since I could get my head under the hood. So, I'm real picky about how things get done. I could go on and on about repair shops and associated screw ups. My observation is that most are not dishonest, just shoddy...or incompetent...or in too much of hurry...or all of the above. I guess I wouldn't mind paying the price if I actually thought they could do a better job than me, workmanship wise. So, I'm stuck having to fix stuff myself 'cause I don't trust anyone else...that's my "cross to bear"...plus I'm cheap.

Mohawkmtrs: to answer your question: Why not just get the OE cat and get it flashed? Well, because the OE cat is gawd awful 'spensive! Seems like I'd be out $800 bucks or so down at the dealer, plus the reflash. So far I'm into it about $250. That's a lot of beer. Plus I get to hear from you guys. Now, if that secondary O2 sensor extender does the job I'll be out $265 total. And in the process, I'll have learned a bunch about P0420 problems.

Here's one for ya: can anyone actually tell me what the reflash does? I understand what flashing is...you are loading new software (firmware actually) into the PROM (OK, I'm an electrical engineer)...but so far no one (on any of the forums I've checked) has actually described in detail what the problem is or what is actually being "fixed". Did the the firmware in the PROM/ECM get corrupted or did Subie come out with a new firmware release to correct problems in the original firmware? And if it's new firmware, what was changed in code?

Thanks again for the great responses. I'll check back.

yes I do work at a dealer and proud of the fact. There are good and bad techs everywhere. The general consensus seems to be that the worst are at dealers and I can tell you they're not. Even the worst dealer tech I know has had more training then the average garage mechanic and i get several calls a week from garage mechanics needing a magic bullet thrown there way from the boys at the dealer. Lots of manufacturers including dodge have flashs for the pcm for those very codes. In a nutshell it changes the parameters for the rear 02 monitor in what constitutes too much switching. These changes are to allow for poor quality fuel, excessive idling etc which all lead to early converter failure. Your cheater bung is just that a cheater because you're raising the nose of the 02 out of the exhaust stream so of course it's not sampling the gasses the same as it should be. There's even sights that tell you how to set up cheater pipes to run no converters and keep the cel off. Think of the money they are saving. I don't care where people fix there cars although that being said I'll put my skills up against anyone anywhere. My whole point and frustration with these codes on anything is because alot of people either buy a converter they don't need because it'd be under warranty but they're too ignorant to check with the dealer or too cheap and uninformed to know the difference between an 800 dollar converter and a 200 dollar so they buy the 200 that doesn't operate as efficently as the oe, they remove there oe and put a cheaper aftermarket on when all they needed was a software flash. That is stupid anyway you slice it

Just to give an example about the "reflashing". Toyota had quite a few early P0420s on the Prius a few years ago. They discovered that the Fuel Strategy Logic in the PCM was causing it(I don't know if it was enriching or enleaning or what). The stoichiometric ratio wasn't the 14.7:1 that is required for optimum efficiency of the cat. So, they issued a recall in a service bulletin that required a reflash of the PCM. That fixed it. So it was a free recall if Im not mistaken, but many people didn't get it done because it didn't sound important. We had one example of that in our shop. She wouldn't go get the reflash for fear of the dealer(she'd never been there but to buy the car. Where would she get the idea that the dealer is "bad"?)
I agree with COMP, and MM, obviously, since we're acquainted here.
Understand something. These vehicles required millions of dollars to engineer the first time. To cheat the original programming is taking the long way from point a to b. Being an "engineer" of a certain field, Im sure you don't need this lowly grease monkey to tell you what the shortest way is from point a to b. So, instead of working around the original programming, work with it. It's easier, less stressful and may even be cheaper when you figure in time wasted, parts purchased, and mistakes made. Shortest distance? - New OE cat.

Jeff, Darkrooms and Mohawk:

I installed the cheater bung and it worked, as I expected it would. So, I'm out of the woods for now at least. I love it when a plan comes together! I really want to say THANKS for all the good information you guys have provided. I realize it takes time and effort to read the posts and reply. In summary, I learned a lot here, including:

1. Aftermarket Cats are one area where it's prolly best to go w/OEM. Having worked on cars for many years, I already new that all parts are not created equal. For example, on my 2000 4Runner I got 90,000 miles out of the front brake pads. That's about double what I get out of Autozone pads. Accordingly, I replaced them with OEM...that one less brake job for me. Main difference is that it didn't cost me and extra $600 bucks to go w/OEM in this case.

2. You guys are great and you know your stuff...even if you are a little defensive.

3. If the old P0420 shows up again I'll prolly bite the bullet and go buy an OEM converter and have the ECM reflashed.

4. The whole ECM reflash thing...I was not aware this could be done, or is done. I'll def. keep that one in mind!

5. I could have saved the $250 I spent on the Cat by just throwing in the cheater bung ($15) when the OEM cat went bad!

6. This forum is a great place to learn more about fixing cars. I'll be around!

Finally, a couple comments:

1 On the Engineer business...I didn't throw that in with the goal of attempting to impress anyone, or to imply any form of superiority. Just wanted to let you know what my knowledge base was. I'm a grease monkey too!

2. This vehicle does not have a MAF sensor (dirty MAF came up as a potential related issue). It uses baro, air temp, throttle position, RPM...all that stuff...etc, to estimate mass air flow. I was a little surprised by that 'cause I figured all the newer vehicles used a MAF. I thought I would clean it...but there's nothing to clean. I did clean the throttle body though. On a related issue, I got a "too lean" code on my 4Runner once and fixed it by cleaning the MAF sensor. BTW: the 4Runner has a TRD blower that I installed back at 9,000 miles...still running strong...130K miles now. Had to replace the pinion bearing in the rear end at around 120K...prolly due to hauling ass with a trailer for long miles and high boost!

3. I take my laptop, with OBD monitor plugged in, on road trips so I can graph various sensor outputs as I drive...particularly if I'm having any problems. OBD truly is fascinating (how's that for geeky?) I monitor fuel trims, O2 sensor outputs, air temp, spark advance, baro, etc. Only problem is keeping an eye on the road!

THANKS AGAIN,

Tele

Bet ya can't wait for OBD III!

Darkrooms: not so sure about that! Been reading a little about it. Sounds like there may be "constitutional issues". I can just see a bunch of lawyers getting involved...lovely...we'll be signing waivers just to start the car!

my girlfriend has a subaru outback 2002 (that was bought in late 2001) with maybe 120k on it. It also has the P0420 code. She has had a new front O2 sensor and now a new rear O2 sensor put on and the P0420 went away for awhile (3 days), long enough to pass the state test, so the mechanic says get a new cat before the next emissions test, which is 2 years from now. Is there a free Flash re-program available for this year and model also? Also, where can I buy the ODB II interface to hook up to a laptop that isn't too expensive? Just a few questions about the previous discussion on aftermarket Cats - it could be they are more prone to setting the code, but I wonder how close they come to doing the intended job of burning all the pollutants - don't some test centers still have the ability to put the instrument up the tailpipe and actually measure what's coming out for pollution? That would be interesting to see if a Subaru with a P0420 and a new aftermarket Cat fails the max allowable polluting or not, or even check the emissions when the original factory one first sets the code. So yes the aftermarket may not make the rear sensor do the right thing to pass the Subaru fault check, but is it doing its job to stay at least just under the emissions limits? - if so, that means subaru's fault code triggers too easily. But if the aftermarket Cat is not doing the right job by letting pollutants through and also setting the code, I would think that makes a case for trying to return it and get a refund, no? Do Cats have a warranty? Also whoever sells them should get some flack for selling a part that doesn't work - Autozone, etc. Most parts have a warranty nowadays, and I didn't think it was the case with most businesses to be selling parts that are bad and you are stuck with them. So maybe they say if you installed it no refund, but if this is a chronic thing with aftermarket Cats and not just random here and there, sounds like a case to go to customer service at Autozone or wherever maybe? I saw a guy on a website that put an oscilloscope on the front and rear O2 sensors on a car - the voltage from the front sensor wanders between I think 0.2 and 0.8 volts about once every second while the car constantly adjusts the mixture. The rear sensor is supposed to sit at a steadier voltage and not fluctuate, I think it sits steadier at a low voltage, like maybe 0.2. My own Dodge caravan has 184,000 miles on it and passes with new O2 sensors. Why do some cars get such a long life out of their cats and others not? seems odd the Subaru tends to fail the factory equipment early and is also sensitive to aftermarket ones - sounds to me like the computer logic is too touchy maybe?. Do other cars flag the cats as bad at near 100k like this?

check out this EPA webpage:

http://www.epa.gov/OMS/cert/factshts/catcvrts.pdf

aftermarket converters have a warranty for 5 years 50,000. they better work $25,000 fine!

The EPA says there are two types. I wonder if some of the problems have to do with buying the wrong one?