vwbuge1 Posted February 8, 2009 Share Posted February 8, 2009 I came up with a P0420 code today. I did some reading and it looks like I am going to replace the o2 sensors. I have had luck buying the universal ones off ebay. So is the stock one a 1 wire or 2 wire? Quote Link to comment Share on other sites More sharing options...
EVOthis Posted February 8, 2009 Share Posted February 8, 2009 (edited) which O2 sensor are you going to replace? I believe the front one has more a chance throwing this code than the rear one but i could vary well be wrong i think it might be the other way around..either way make sure first of all you dont have any exhaust leaks.....Anyways if your going to try replacing the sensors personally i would go OEM for the front one if not both...there are tons of threads on here about aftermarket O2 sensors causing problems and such...as seen...Subarus seem to be touchy when it comes to certain aftermarket componants...O2 sensors being one of them...how many miles are on the car? what year/model? Have the cat. conv.'s ever been replaced? Edited February 8, 2009 by EVOthis Quote Link to comment Share on other sites More sharing options...
vwbuge1 Posted February 9, 2009 Author Share Posted February 9, 2009 2000 Outback Limited. Car has 113k and a fairly new exhaust. I have only owned it 4 days now. I had luck using a universal o2 sensor on my dad's '97 Outback. I figured for the money I'd give it a shot on mine. I was going to replace both front and back. Quote Link to comment Share on other sites More sharing options...
Rooster2 Posted February 9, 2009 Share Posted February 9, 2009 In my opinion it is still far better to buy an O2 sensor that is designed specifically for your model Subie. My experience in using a generic sensor, is that no matter how hard I tried to attach the OEM connector to a generic sensor, it has usually failed in about a year or so. This is experience in applying a generic to a number of makes of cars. I finally came to the conclusion that spending the extra $20 or so is money well spent, in not having to do the job a second or third time. Quote Link to comment Share on other sites More sharing options...
vwbuge1 Posted February 9, 2009 Author Share Posted February 9, 2009 Extra $20? Where are you buying your 02 sensors? OEM is well over $100. I can get a generic for $30. I put one on my dad's Outback last year and it is holding up. I also put a generic on my wife's Expedition 2 years ago and it is still holding up. Quote Link to comment Share on other sites More sharing options...
abog Posted February 9, 2009 Share Posted February 9, 2009 Heated O2 sensors have 3 wires. Quote Link to comment Share on other sites More sharing options...
Rooster2 Posted February 9, 2009 Share Posted February 9, 2009 Extra $20? Where are you buying your 02 sensors? OEM is well over $100. I can get a generic for $30. I put one on my dad's Outback last year and it is holding up. I also put a generic on my wife's Expedition 2 years ago and it is still holding up. At Parts America dot com, Subie OB generic Bosch 02 for $62, exact Bosch OEM replacement for $98 with one day delivery. Yea, guess that is closer to a $40 price differential, but less than the "well over $100" someone quoted you. I have had good performance from Bosch O2 sensors, spark plugs, and plug wires in my two Subies. How are you splicing the wires to the generic to get long term succcess? I would like to know and learn how. Quote Link to comment Share on other sites More sharing options...
vwbuge1 Posted February 10, 2009 Author Share Posted February 10, 2009 At Parts America dot com, Subie OB generic Bosch 02 for $62, exact Bosch OEM replacement for $98 with one day delivery. Yea, guess that is closer to a $40 price differential, but less than the "well over $100" someone quoted you. I have had good performance from Bosch O2 sensors, spark plugs, and plug wires in my two Subies. How are you splicing the wires to the generic to get long term succcess? I would like to know and learn how. I was assuming that the 02 sensor was a two wire. I am now told the one on the car is a three wire. I have spliced connectors on my wife's Expedition with success. Quote Link to comment Share on other sites More sharing options...
johnceggleston Posted February 10, 2009 Share Posted February 10, 2009 the last time i looked, the front and rear o2 sensors were exactly the same, denso, (96 legacy) just the connectors were different. both are 3 wire units, one has a 3 wire connector and the other a 4..... shop at your own risk. it's hard to know how long some parts will last. but if the factory part lasted 120k miles, ....... Quote Link to comment Share on other sites More sharing options...
The Scooby Posted February 10, 2009 Share Posted February 10, 2009 good luck with that, subaru's are VERY picky with their parts, put a non-OEM thermostat in the engine, most of the time it will stick within a week. buy the bosch OEM replacement and don't worry about it for another 10 years or so. but just to let you know, the reason you got a P0420 code is because its your cats, not your O2 sensor. Quote Link to comment Share on other sites More sharing options...
vwbuge1 Posted February 10, 2009 Author Share Posted February 10, 2009 good luck with that, subaru's are VERY picky with their parts, put a non-OEM thermostat in the engine, most of the time it will stick within a week. buy the bosch OEM replacement and don't worry about it for another 10 years or so. but just to let you know, the reason you got a P0420 code is because its your cats, not your O2 sensor. I have read quite a few posts about the P0420 code. Half say it is the o2 sensor, half say it is the cats. I guess you fall into the latter half. I just don't see how the cat can be ruined in just over 100k miles. Quote Link to comment Share on other sites More sharing options...
The Scooby Posted February 10, 2009 Share Posted February 10, 2009 then i guess you don't work on cars for a living, just like the other half. whats going to happen is you will put in a after market O2, it does not read as good as a OEM, thats why the code will go away for a while. but im just a guy who works on subarus for a living for the last 10 years or so. Quote Link to comment Share on other sites More sharing options...
bratman18 Posted February 10, 2009 Share Posted February 10, 2009 po420 stands for catylist efficiency below thresh hold. Which states right in there is the cat. I agree with The Scooby. A large reason for this code is the crappy regular gas that is sold now. Try running a higher octane gas and maybe even an octane booster. Hold off on replacing the 02 senso Quote Link to comment Share on other sites More sharing options...
The Scooby Posted February 10, 2009 Share Posted February 10, 2009 po420 stands for catylist efficiency below thresh hold. Which states right in there is the cat. I agree with The Scooby. A large reason for this code is the crappy regular gas that is sold now. Try running a higher octane gas and maybe even an octane booster. Hold off on replacing the 02 senso yes, thank you, reason being is that if it was the o2, it would state that oxygen sensor bank 1 or bank 2 if it was the o2. Quote Link to comment Share on other sites More sharing options...
abog Posted February 10, 2009 Share Posted February 10, 2009 When splicing a connector for an O2, you should solder the connection and heat shrink to seal the connection from the elements. Quote Link to comment Share on other sites More sharing options...
vwbuge1 Posted February 10, 2009 Author Share Posted February 10, 2009 then i guess you don't work on cars for a living, just like the other half. whats going to happen is you will put in a after market O2, it does not read as good as a OEM, thats why the code will go away for a while. but im just a guy who works on subarus for a living for the last 10 years or so. Excuse my ignorance as someone who doesn't work on cars for a living. My original comment was just stating fact, I am sorry you took it the wrong way. From all the posts I have read I assumed it could be either the O2 sensors or the cat going bad. Taking the least expensive route, I thought I'd try to replace the o2 sensors first. I am guessing that the rear sensor could be bad? How does the ECU know that the cat is going bad? From the data received from the rear O2 sensor? Last resort for me is to spend several hundred dollars replacing a cat on a car that I just bought. Quote Link to comment Share on other sites More sharing options...
The Scooby Posted February 10, 2009 Share Posted February 10, 2009 it says a bad cat right in the title, thats why i do not understand why people think its the o2's. if it was it will throw a o2 code. and thats why you diagnose the problem, rather then throw parts at it. its throwing a code with Catalyst efficiency below threshold, not o2 efficiency, the ECU knows how the cats are doing by taking readings from both the front and rear to make sure that they are working properly. Quote Link to comment Share on other sites More sharing options...
johnceggleston Posted February 10, 2009 Share Posted February 10, 2009 so why does the code go away when you install an oem o2 sensor? it's worked for lot's of people. Quote Link to comment Share on other sites More sharing options...
The Scooby Posted February 10, 2009 Share Posted February 10, 2009 so why does the code go away when you install an oem o2 sensor? it's worked for lot's of people. hey if you don't believe me, then think what you want, not trying to get into a debate. Quote Link to comment Share on other sites More sharing options...
vwbuge1 Posted February 10, 2009 Author Share Posted February 10, 2009 so why does the code go away when you install an oem o2 sensor? it's worked for lot's of people. I am glad someone else spoke up. I was beginning to think I read all the wrong posts. I am not debating fact but just asking this question. The ECU knows there is a problem with the efficiency of the cat by taking data from pre and post cat O2 sensors. What if there is nothing wrong with your cat but something wrong with the post cat O2 sensor? Quote Link to comment Share on other sites More sharing options...
The Scooby Posted February 11, 2009 Share Posted February 11, 2009 then it would throw a O2 code. im done trying to help people out, they just want to argue... Quote Link to comment Share on other sites More sharing options...
vwbuge1 Posted February 11, 2009 Author Share Posted February 11, 2009 then it would throw a O2 code. im done trying to help people out, they just want to argue... didn't know I was arguing........ Quote Link to comment Share on other sites More sharing options...
abog Posted February 12, 2009 Share Posted February 12, 2009 The ECU gets input from the front and rear 02 sensors and determines catalyst efficiency. As everything ages the signals will change, the ECU has the ability to learn and age with the rest of the components. In order for the ECU to throw a code for an 02 sensor there would have to be a reading from one or the other that was totally different than the readings that the ECU was used to receiving. while the readings in catalyst efficiency will gradually change as the car ages, the ECU will not be concerned with this until the readings fall to a predetermined unacceptable level. Which sounds to me like what you have. A car that has this condition will act ok for a while on new sensors because the ECU is learning the characteristics all over again. It has been my experience with this that I have seen converters fail at much lower mileage than you have, reasons are many, but depending on fuel quality, tune up practices etc. they can go out prematurely. I would recommend replacing the cat and if you can afford it, replace the 02 sensors as well. IMHO 100,000 miles is a good time to replace 02 sensors anyway, just like spark plugs. Quote Link to comment Share on other sites More sharing options...
vwbuge1 Posted February 12, 2009 Author Share Posted February 12, 2009 The ECU gets input from the front and rear 02 sensors and determines catalyst efficiency. As everything ages the signals will change, the ECU has the ability to learn and age with the rest of the components. In order for the ECU to throw a code for an 02 sensor there would have to be a reading from one or the other that was totally different than the readings that the ECU was used to receiving. while the readings in catalyst efficiency will gradually change as the car ages, the ECU will not be concerned with this until the readings fall to a predetermined unacceptable level. Which sounds to me like what you have. A car that has this condition will act ok for a while on new sensors because the ECU is learning the characteristics all over again. It has been my experience with this that I have seen converters fail at much lower mileage than you have, reasons are many, but depending on fuel quality, tune up practices etc. they can go out prematurely. I would recommend replacing the cat and if you can afford it, replace the 02 sensors as well. IMHO 100,000 miles is a good time to replace 02 sensors anyway, just like spark plugs. That was the most informative explanation I have read. When the readings fall to a predetermined unacceptable level....."below threshhold" It all makes sense. I erased the code and put in some better fuel and an additive. I am sure that the CEL will come on again. I planned on two new o2 sensors with the new cat. So what is everyone's experiences with new cats? I see the OEM one from Subaru is around $900. I see others with both cats in one pipe as low as $250. Can I get away with a non-Subaru cat? Quote Link to comment Share on other sites More sharing options...
abog Posted February 12, 2009 Share Posted February 12, 2009 Have seen many non OEM cats, they seem to work ok. Hard to beat the quality of the Subaru parts. But hard to swallow the price Quote Link to comment Share on other sites More sharing options...
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