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catalytic converter question


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10 replies to this topic

#1 hlevyn

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Posted 20 June 2004 - 04:31 PM

heya guys. had the check engine light on despite the fact that the car felt like it was running great. took it by the dealer and found the code to be a catalytic converter code. the guy there said it's most likely just something in there either blocking the o2 sensor, or something just bumped it. the light's off atm, and i'd like to keep it that way. any suggestions on what i can do to clean things out in there? is there anything i can do? thanks!

#2 hohieu

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Posted 20 June 2004 - 09:52 PM

Depending on the state, it is illegal for shops to service or tamper with the catalytic converter (cc). If your car is running fine, I wouldn't worry about it. How many miles do you have on your car? Has the post-ccO2 sensor been changed? This sensor does not affect performance, but it does monitor the performance of the cc. A bad sensor may be annoying by way of the indicator light, but it will not cause any damage to your vehicle. These sensors are relatively inexpensive and easy to install. If you should decide that you want to replace it yourself, check www.oxygensensors.com and do a search on this site.

Also, if your car is running "great"and you gas milelage is normal then your cc and pre-cc O2 sensor are fine. The only way to maintain your cc is to to take care of your vehicle by performing the recommended engine maintenance (i.e. spark plugs, air filter, fuel filter) at factory recommended intervals and by avoiding certain fuel additives that contaminate the precious catalysts.

#3 hlevyn

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Posted 20 June 2004 - 11:24 PM

thanks. it's a 2000 outback with > 107k miles on it. feels like it's running fine. gas mileage dipped a good bit last tank, but seems to be back to normal on this one. i bought the car back in feb, and am not sure if the post-ccO2 sensor been changed (any easy way to check?). the air, oil, and fuel filters were also changed ~5k miles ago, and the plugs, wires, coil, and 2 fuel injectors on it are new due to a misfire i was having.

i'm not terribly worried about it, but would just like to make sure things keep running smoothly and would also like to avoid the annoyance factor of having the cel come on.

thanks for the response =)

#4 hohieu

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Posted 21 June 2004 - 09:39 AM

The only way to check the condition of the O2 sensor, aside from the Engine management computer (emc), is to take it out and look for contamination - not disimilar to checking the condition of spark plugs. Oxygensensors.com should have helpful photos if you plan on performing this task yourself. At 107K miles, it's doubtful that your rear (post or downstream from cc) oxygen sensor has been replaced as it does not affect performance. It just monitors the exhaust leaving your tail pipe, therefore, most people don't ever replace it.

As for the front catalytic converter, you may want to replace it as preventive maintenance - I plan to replace mine when I change the timing belt at 105 K. It detects the amount O2 in comubstion gasses, and this info. is processed by the emc in order to achieve optimal fuel-air mixture or stoichiometric ratio. The emc is constantly adjusting the fuel/air ratio because the amount of O2 depends on environmental variables (i.e. temperature, altitude, pressure). Your temporary poor fuel mileage may have been just a fluke, but poor fuel mileage and engine perfomance are indications of a bad O2 sensors. Check to see if the dealer replaced it when they serviced your fuel injection system. If not, you can pick one up online and do it rather cheaply if you are so inclined- it's as easy as changing a spark plug. Other members of USMB report that Bosch supplies these sensors to Subaru. All you need is an open end 22mm wrench. Just make sure you put some of the antiseize that should come with the sensor on the threads in order to facilitate easier future replacement. Take care.

#5 harborseal55

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Posted 21 June 2004 - 10:13 AM

I had (have) the same condition (CEL indicating CC reduced efficiency) that I thought was most likely a rear O2 sensor problem. Bought a new sensor (Bosch O2 for rear was nearly $150 from my local NAPA auto parts), and unfortunately the threaded fitting in the CC that the sensor screws into snapped out of the CC upon my attempt to remove the old O2 sensor. Ugh! My 96 Legacy has 170K, and I currently have the gaping CC hole plugged with a 1/2-inch pipe thread plug, inserted by using a 1/2-inch NPT tap that was able to create enough threads in the CC hole to insert the plug. So this is just a note to beware that this is a possibility, and the permanent fix is not easy. This temporary plug fix was fairly easy, has been in place for a few weeks now, the car still runs as great as always, and my scanner doesn't indicate any new codes other than the original "reduced CC efficiency" code. I still plan to try a permanent repair in a few weeks, likely see if I can get a new threaded insert, remove the old CC, and see if someone will weld the threaded insert onto it so that I can reinsert the new rear O2 sensor.

#6 hlevyn

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Posted 21 June 2004 - 11:27 AM

thanks guys. i'm a poor college student who's working to cover rent, food, and gas. when i have $150 of disposable income i'll see about replacing it. take care!

#7 hohieu

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Posted 21 June 2004 - 07:05 PM

thanks guys. i'm a poor college student who's working to cover rent, food, and gas. when i have $150 of disposable income i'll see about replacing it. take care!


I empathize with your plight, but an 00 Outback is not a bad ride for a college student. I am a graduate student, and yes, it's true: we really do live below the poverty line. In any case, you can get a universal rear O2 sensor at the above website for about $60 including shipping - just need to use the old connector. The more important front sensor is about twice as much. Take care.

And Harborseal55,
Good luck with the sensor. Can you use a helicoil or are you past the point of no return?

#8 harborseal55

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Posted 22 June 2004 - 09:18 AM

Hoheiu, good idea, but installation of a HeliCoil isn't an option in this case because it's not that the threads were damaged, but that the entire thick metal section itself that contains the threads that was welded onto the sheet metal CC body tore off of the CC, weld and all, leaving a sheet metal hole. Using the National Pipe Thread (NPT) plug worked only because NPT threads are tapered so the plug gets larger as you screw it further into the hole, making it fit tighter.

Interesting that you said that the front O2 sensor was more expensive. I also bought a new Bosch front O2 sensor from NAPA too, and it was less than the rear sensor (Front was about $100, and rear was about $150, different part numbers).

#9 hohieu

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Posted 22 June 2004 - 11:36 AM

Yeah, it's pretty weird: The rear sensor for my forester is also more expensive than the front one. For some reason, it's the opposite for MY '00 Legacy Outbacks for which this site also lists different prices for AT and MT vehicles. Since the engines are the same on this car and the my car, I wonder if it's the connector that makes for the price differences. It's a mystery, and I wonder if these prices have to do with marketing issues (supply + demand) or manufacturing issues (that these sensors are all acutally different).

Does the NPT plug have threads on the insider? For a permanent fix, I imagine that you could get somebody to weld the sensor housing back into the header pipe for a nominal fee if the metal around the opening is still good.

#10 harborseal55

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Posted 23 June 2004 - 04:01 PM

Someone in a previous thread (my original post asking what I could do regarding the threaded section having torn loose from the CC) suggested getting a threaded piece from a performance/speed shop that would likely have them for adapting fuel injection to engines and have someone weld this onto my catalyst. I still plan to follow that scheme as the permanent repair, as replacement CC appear to only be available from Subaru and are about $700 (or more if memory serves me right) just for the front CC (eek! I seem to remember a quote of around $1200 for both front and rear catalysts). I sure hope that that solves the problem. I'll be a bit p_ssed if the "Reduced Catalyst Efficiency" code is still triggered after clearing the codes.

#11 cleeoutback

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Posted 21 October 2004 - 12:00 AM

Hi all, I'm a new user AND know close to zip about car maintenance.

My CEL finally went off this past week. It's been on for about 3 months. I got a $1200 estimate from an Oakland Subaru dealer. Instead, I purchased the parts from that same dealer for $900 (20% off on Wed nights) and paid a local mechanic $80 to install it. After installation, I had to drive for a few days before the light went off.

I tried to buy a universal CC but it wasn't available for my 97 outback.




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