CAT efficiency code- suggestions for replacement?

[gijoe985]

I a getting the "Catalytic Converter is below efficiency threshold" code on my wife's 2001 2.5l outback. I have cleared it a couple times (in case it was a fluke), but it has came back. I figure that I am going to need to replace it. I was curious, would it possibly be cheaper to get a generic high performance cat? I figure if it even helps with gas mileage a little bit, it'd be worth it. She commutes almost 100 miles a day in that car.

 

Any other suggestions?

[Cougar]

Replacing the CAT my not fix the trouble. There could be other things causing the error code to appear. The rear O2 sensor may be bad for one thing. You do want to fix whatever the trouble is so the CEL isn't on and you can tell when other things happen.

Edited July 1, 2010 by Cougar

[GeneralDisorder]

Lots of info on this around here.

 

1. Basically - most people have bad luck with aftermarket cats and sensors.

 

2. It could be the cat, but it also could be the sensors, or possibly exhaust leaks, or combinations of all three. Typically you replace the sensors first (front and rear) and only replace the cat if the code comes back again and if the code continues to return then it's down to finding and fixing leaks, etc.

 

3. It's very expensive. Alternatively you can install a spark plug non-fouler between the exhaust and the rear sensor to lean out the signal from the rear sensor and placate the ECU's sensitive catalyst check routine. Fixing it the right way could cost near $750 to $1000. Fixing it with a non-fouler is less than $10.

 

GD

[idosubaru]

it's not the sensor itself, or highly unlikely i should say. although i'm sort of inclined to replace them as GD suggests because i plan on keeping the cars another 100,000 miles or more. if i have these codes at 200,000+ miles i might reconsider.

 

this is covered a lot here and sparks some strong opinions. if you look right now at the bottom left you'll see "similar threads". there's also a search function which shows lots of previously covered info about this issue.

 

rear sensor is doing nothing, it's just a monitor, so this code is benign. the front sensor is the one that affects gas mileage and actual engine characteristics. the rear is just a monitor that has horribly tight thresholds which cause problems if you look at it funny.

 

the issue is that the tolerances are too narrow, so how you go about fixing that is your decision.

 

first make sure you don't have any leaks in the exhaust, a leak alone will cause this, because the tolerances.

 

best bet, and what i and others do, is to fix it for $6 with two anti-fouler trick, lots of information on that posted here. they even sell little adapters on ebay that do it for you. remove rear sensor, install this adapter, reinstall O2 sensor. you're done for $6. this sort of "increases" the tolerances to a more acceptable level.

 

aftermarket might work. replacing with anything other than Subaru leaves certain percent of folks that still have the issue...or it comes back in a year or two. again - tolerances are the issue, minor differences can cause issues.

 

Subaru units are insanely expensive.

Edited July 1, 2010 by grossgary

[cagranitz]

I totally agree with grossgary's comments about the tight tolerances for the rear sensor. I have a 2001 Outback Wagon EJ251 engine, 4EAT auto trans with 147,000 miles. The car had been throwing the P0420 Cat Efficiency code at widely spaced times (every 3 or 4 months).

 

Since neither the front or rear sensors had ever been replaced I figured it was high time to install new ones. I went ahead and installed brand new genuine Subaru front and rear sensors about 2 months ago.

 

About 2 weeks after I installed the new sensors the CEL came on again with the same P0420 code. I got under the car and looked carefully for any leaks. It all looked tight as a drum. I cleared the code.

 

About a week after that I had the state inspection done and it passed the emissions test with no problems. This would seem to indicate that the catalytic converter is fine.

 

Last week we were on a long trip (1400 miles) with the car. At 3 random times the CEL came on with the same code.

 

The engine runs great, gets good gas mileage, has good power, has fresh oil, new PCV valve, new air filter, and spark plugs that have about 20k miles on them. So it is well tuned.

 

Thus, since it passed emissions, runs great, has new front and rear sensors, and no exhaust leaks, I have to believe the CEL code keeps coming back due to the tight tolerances on the rear sensor.

 

I will simply continue to clear the code when it appears. If it got much worse then I would likely use the anti-fouler trick.

[gijoe985]

Well, turns out that today, when I went to check the code one last time... it came back different. Now I got a 133- b1s1 o2 sensor slow response.

 

Any thoughts on that. I'm going to go search...

 

 

Edit- After some searching, it seems that looking for leaks is going to be needed. I've been getting some rattling for a long while from the heat shielding on the exhaust.

 

I'm supposed to go on a trip from WA to CA pretty quick here. Will this be a problem? I highly doubt it, other than maybe a fuel mileage drop...

Edited July 1, 2010 by gijoe985

[idosubaru]

no, O2 sensors won't cause any drivability issues at all.

 

never tried it on newer stuff but older stuff drives fine with the O2 sensor unplugged.

[Cougar]

Going from what some others have said when they changed out their old O2 sensors missing problems were cleared up after the change.

[subaru360]

no, O2 sensors won't cause any drivability issues at all.

 

never tried it on newer stuff but older stuff drives fine with the O2 sensor unplugged.

 

 

Not true, I've have bad front O2 sensors cause major driveability problems. Even on obd1 cars which is what I consider old stuff. Surging at cruising speeds is common. Hesitaion from a stop happens a lot too.

 

 

But anyway for the 420, aftermarket cats will NOT fix it. They don't work well enough. Factory cats will but are mega expensive, sometimes more than the car is worth. I just do the antifoulers, it works 9 times out of 10 for me.

[idosubaru]

Not true, I've have bad front O2 sensors cause major driveability problems. E.

good call. would it cause it to be "not driveable"? to be stranded by an O2 would be odd i would think.

 

anyone ever find out if you can drive with them unplugged like you can older gen stuff?

Edited July 2, 2010 by grossgary

[heartless]

wish i had tried unplugging when the O2 went bad on my 90 lego - never occured to me to do/try that.

 

But yeah, i had major driveability issues when mine went south - miss, cough, no power - just ran like crap in general. New O2 and she runs like a dream - even increased my fuel mileage from an average of 27.5 to more like 30mpg! and this is an AWD 4EAT car! last fillup i checked i even broke 31 mpg!

[gijoe985]

Not to hijack my own thread, but I really wish I could get the fuel mileage up on my wife's car. Again, a 2001 2.5l awd auto outback. So i think that is the same tranny. Not certain though. I think she only gets like 25mpg... It'd be sweet to see a few more mpgs on our 2500 miles trip next week...

[idosubaru]

everything is working against gas mileage. 4WD. Automatic. Outback - wagon, roof racks, higher stance. It's just not meant to be a good gas mileage vehicle. highway mileage could see a little better and you'll do better at 60 instead of 75 mph as well, but that's hard to do!

[subaru360]

You won't be stranded by an O2 sensor, but the car can be a handful to drive, hesitating with no power. I've almost been run over trying to pull out in a car that had a bad O2. They do run with it unplugged. When it sets an O2 sensor code the computer ignores the sensor input and goes to backup fueling or what some people refer to as "limp mode".

[Petersubaru]

if you are having driveability issues because the O2 sensor failing..go up to 89 or 91 octane..should bring back smoothness.. a change in gas stations cleared up the "cat eff." problem for me..perhaps a coincidence, time will tell