tests for a catalytic converter?
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More Turbo
Joined: Nov 2004
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From: colorado
tests for a catalytic converter?
My wife's 2000 Subaru Outback has been having the check engine light come on (sometimes it goes of by itself, sometimes we reset it) We took it in to have the codes checked and the mechanic said it was the catalytic converter and the o2 sensor. Said $600.00 would fix it. Doing some poking around I found out the Subaru has two converters and two o2 sensors. I guess the first sensor read the exhaust before the conversion ad the second one reports how it changed. Is there some way to tell if one cats bad and the others ok? How about the sensors? I hate to replace all four components if it's just one sensor reading bad. Also the car has 150000 miles on it so maybe I should just quit crying and replace them all... Any suggestions?
ps. She also gets a strong antifreeze and oil smell every so often , could this be related or you think I've just got more problems? Thanks for any help!
ps. She also gets a strong antifreeze and oil smell every so often , could this be related or you think I've just got more problems? Thanks for any help!
Cargo Master
Joined: Nov 2003
Posts: 2,585
Likes: 1
From: Duluth, Mn.
Is common on Subarus. They are sensitive to after market O2 sensors. OEM's work much better.
Plenty of info here> Ultimate Subaru Message Board
Plenty of info here> Ultimate Subaru Message Board
Super Moderator
Joined: Apr 2004
Posts: 34,499
Likes: 2,811
Trade it off on an '07 or '08 pre-owned at your Suby dealer. Car sales suck so bad, they won't notice the black tape over the CEL.
It sounds like you are due for a serious Axx whuppin' repair wise, so NOW is the time to send it down the road, IMBUDO.
It sounds like you are due for a serious Axx whuppin' repair wise, so NOW is the time to send it down the road, IMBUDO.
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
Why get a new car when the one he has might be reliable, in good shape, well-maintained and with low miles? A few hundred bucks spent on it - or about two months of car payments - might fix what's wrong with it.
It could be the O2 sensors themselves causing a bad reading, and any mechanic that doesn't suggest that be the first thing to try probably isn't worth going back to. Here's a link someone posted a while ago about how to test your O2 sensors. They can be pricey to replace, so if you're interested in saving money it's good to know how to test them.
Oxygen Sensor Information
It could be the O2 sensors themselves causing a bad reading, and any mechanic that doesn't suggest that be the first thing to try probably isn't worth going back to. Here's a link someone posted a while ago about how to test your O2 sensors. They can be pricey to replace, so if you're interested in saving money it's good to know how to test them.
Oxygen Sensor Information
Sit. Stay.
Joined: Oct 2001
Posts: 18,308
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From: Washington State
Why Andy! I had no idea you participated in technical threads! 
Why we didn't even mention religion or politics...
Why we didn't even mention religion or politics...
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Super Moderator
Joined: Apr 2004
Posts: 34,499
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Why get a new car when the one he has might be reliable, in good shape, well-maintained and with low miles? A few hundred bucks spent on it - or about two months of car payments - might fix what's wrong with it.
It could be the O2 sensors themselves causing a bad reading, and any mechanic that doesn't suggest that be the first thing to try probably isn't worth going back to. Here's a link someone posted a while ago about how to test your O2 sensors. They can be pricey to replace, so if you're interested in saving money it's good to know how to test them.
Oxygen Sensor Information
It could be the O2 sensors themselves causing a bad reading, and any mechanic that doesn't suggest that be the first thing to try probably isn't worth going back to. Here's a link someone posted a while ago about how to test your O2 sensors. They can be pricey to replace, so if you're interested in saving money it's good to know how to test them.
Oxygen Sensor Information
YMMV as always.....
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5th Wheeling
Joined: Oct 2008
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I've been lurking for awhile now and I find it amusing that my first post is about a Subaru OB (I own a '97 OBW). Check this site/thread for everything you ever wished to know about Outback O2 Sensors, Cats and related codes/CEL:
SUBARU OUTBACK - P0420 check engine light: read if you've had this
As someone else posted, go OE on the O2 sensor or save a few bucks and go Bosch (they make the OE ones).
SUBARU OUTBACK - P0420 check engine light: read if you've had this
As someone else posted, go OE on the O2 sensor or save a few bucks and go Bosch (they make the OE ones).
Post Fiend
Joined: Jun 2002
Posts: 13,873
Likes: 3
From: Atlanta GA
In the FWIW category, as mentioned, probably the 02 sensor(s) and only use OEM.
It is far easiest and quicker to replace both O2 sensors, then do an on the road test. Then you end up replacing the sensor usually anyways on a high mileage car. The road test usually requires an expensive tester or laptop based system to store data so you can read the voltage levels later.
On Ford and especially GM, an exhaust back pressure gauge can usually determine a failing cat. because they clog. Tester is about $120, they usually have them at muffler places.
Pretty much applies to any car.
It is far easiest and quicker to replace both O2 sensors, then do an on the road test. Then you end up replacing the sensor usually anyways on a high mileage car. The road test usually requires an expensive tester or laptop based system to store data so you can read the voltage levels later.
On Ford and especially GM, an exhaust back pressure gauge can usually determine a failing cat. because they clog. Tester is about $120, they usually have them at muffler places.
Pretty much applies to any car.
Elder User
Joined: Sep 2003
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From: Central, MA
Vacuum Gauge troubleshooting
Using A Vacuum Gauge
Post Fiend
Joined: Jun 2001
Posts: 5,228
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From: Running Springs CA
Cats can die without clogging or excessive backpressure, so that is not a complete test. I would replace the sensors and see if they still indicate a bad cat. $600 for cat and sensors, if that includes labor, is cheap. An aftermarket cat, not including sensor, for the BMW was $1100 at a muffler shop. Dealer price was $1700 plus installation.
Jim
Jim
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More Turbo
Joined: Nov 2004
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From: colorado
"$600 for cat and sensors, if that includes labor, is cheap. An aftermarket cat, not including sensor, for the BMW was $1100 at a muffler shop. Dealer price was $1700 plus installation."
Funny how you can go from feeling picked on to feeling lucky in three seconds! Could be worse! I think I'll just suck it up and either have the mechanic replace the whole she-bang or see if Subaru is reasonable enough on a direct-fit unit with both cat (found them on line fore $300.00 but would rather give my money locally where I can find them later!)I tried all my local auto parts stores and it seems everyone can just get the front one. as far as head gasket leaks, I did a visual around the head to block seal and saw nothing, there's no smoke coming out the back, white, blue or black- and the oil looks clear, not milky so maybe I'm ok. I did find two radiator hoses that had leaked a little and were squishy I replaced them yesterday, they had dripped onto a plastic cover that covers the whole bottom of the engine compartment - I think maybe it was blowing back on the exhaust. At least that's what I'm telling myself! Thanks for all your help!
Funny how you can go from feeling picked on to feeling lucky in three seconds! Could be worse! I think I'll just suck it up and either have the mechanic replace the whole she-bang or see if Subaru is reasonable enough on a direct-fit unit with both cat (found them on line fore $300.00 but would rather give my money locally where I can find them later!)I tried all my local auto parts stores and it seems everyone can just get the front one. as far as head gasket leaks, I did a visual around the head to block seal and saw nothing, there's no smoke coming out the back, white, blue or black- and the oil looks clear, not milky so maybe I'm ok. I did find two radiator hoses that had leaked a little and were squishy I replaced them yesterday, they had dripped onto a plastic cover that covers the whole bottom of the engine compartment - I think maybe it was blowing back on the exhaust. At least that's what I'm telling myself! Thanks for all your help!
Hotshot
Joined: Oct 2002
Posts: 18,488
Likes: 22
From: The Big, Oregon
A quick check is to use a non-contact pyrometer (infrared thermometer, about $40 from Harbor Freight). Run the car normally, and with it still running, check the temp of the pipe just before the cat, and the temp after. If they are within 100º of each other, or the outlet is cooler, replace the cat. If the outlet is more than 100º hotter, then replace the O2s, since the cat is fine.
Butt-Head
Joined: Apr 2004
Posts: 9,449
Likes: 2,934
From: Reed Point, MT
If you've got codes indicating catalyst efficiency, then you need a catalytic converter; plain and simple.
A plugged catalytic converter will rarely ever set a code...although you'll notice a severe lack of power and possible MAF sensor codes.
The ECM is programmed to run a test measuring the oxygen holding capabilities of the catalyst substrate.....if it can't hold or release oxygen in the exhaust stream, the post-cat O2 sensor will see it and the ECM will set the efficiency code.
Don't put O2 sensors on it....just whichever catalyst will fix the code.
OR
Put black tape over the CEL because a P0420 will not cause any driveability concerns. If you have to do it for inspection/registration reasons, you're going to have to pay.
A plugged catalytic converter will rarely ever set a code...although you'll notice a severe lack of power and possible MAF sensor codes.
The ECM is programmed to run a test measuring the oxygen holding capabilities of the catalyst substrate.....if it can't hold or release oxygen in the exhaust stream, the post-cat O2 sensor will see it and the ECM will set the efficiency code.
Don't put O2 sensors on it....just whichever catalyst will fix the code.
OR
Put black tape over the CEL because a P0420 will not cause any driveability concerns. If you have to do it for inspection/registration reasons, you're going to have to pay.