nvr-enuf Posted January 25, 2012 Share Posted January 25, 2012 I did a search on the dreaded P0420 code so I do know that likely my front O2 sensor could be bad / or I could put a spacer in the rear. The Vag-Com states "P0420 - Catalyst System; Bank 1: Efficiency Below Threshold". Does this tell me which sensor that the car is having issues with which could narrow down my problem? Thanks everyone - I want to fix the problem since we are selling the 2002 subie outback sedan, been a great car but wife needs a mini van. She still wished that Subie made a mini van. Link to comment Share on other sites More sharing options...
whitetiger Posted January 25, 2012 Share Posted January 25, 2012 it will be the one after(downstream) the cat. Link to comment Share on other sites More sharing options...
nvr-enuf Posted January 25, 2012 Author Share Posted January 25, 2012 Really? everyone seemed to state that the lead O2 sensor is the one that typically goes. Are you saying it is the one after the cat due to the code from the Scan gauge or based on your experience? If downstream, where would I get the spark plug fowling fitting that everyone talks about? Link to comment Share on other sites More sharing options...
whitetiger Posted January 25, 2012 Share Posted January 25, 2012 Are you saying it is the one after the cat due to the code from the Scan gauge or based on your experience? both. p0420 is a cat efficiency code. this code is specifically triggered by the rear 02 sensor seeing that the cat is not doing its job. this code is the most common exhaust code one can get. we see it all the time. 2 things can make the sensor throw the code. either the sensor is borked, which means you buy a new sensor, or the sensor is functioning properly, which means your cat may need replacement. start with a new sensor(fairly cheap) and see if that solves the issue, you dont want to have to spend lots on a new cat if you dont have to. in contrast, the front (upstream) o2 sensor is the one that ECU uses to tune the engine in closed loop operation. if that one goes, the car will run like crap and you will have misfire/lean/rich codes. Link to comment Share on other sites More sharing options...
BeKnwn Posted January 25, 2012 Share Posted January 25, 2012 Quick questions I've been having. I was meaning to replace the sensors on mine aswell but as for the spacer would it be wise to get one for both front and back or just the back? Link to comment Share on other sites More sharing options...
whitetiger Posted January 25, 2012 Share Posted January 25, 2012 the only point for getting the spacer is if you have an aftermarket hi-flow cat that will cause your rear sensor to throw the code. the space moves the rear sensor out of the exhaust stream so it wont see the fact that the hi-flow cat is not cleaning the exhaust as well as the oem one did. If you have functioning OEM cats, there is no need for a spacer. never put a spacer on the front sensor or your ECU wont be able to get an accurate reading on how the engine is running. Link to comment Share on other sites More sharing options...
BeKnwn Posted January 25, 2012 Share Posted January 25, 2012 (edited) Yeah I have random tech cat and was just wondering thanks Because I was throwing an code on the oem cats sense I've gotten the car and I don't throw a code with the random unless I go on the freeway more then like 5 miles I do a mile everyday on the freeway to get to work no code but more then that yeah lol so imma get new stuff Is there any reccomended spacer or are they all pretty much universal? Edited January 25, 2012 by BeKnwn Link to comment Share on other sites More sharing options...
johnegg Posted January 25, 2012 Share Posted January 25, 2012 (edited) the error code will specify ''bank'' and sensor number. on a typical 2 sensor H4 subaru, bank 1 (there is only one bank on a gen 3 H4 engine) sensor 1 is the o2 before the cat. sensor 2 would be the o2 after the cat. i don't think the ''spacer'' will correct the p0420 code on stock subaru equipment on gen 3 cars. i THINK they closed that loop hole and the system will throw a different code. but i'm not sure. on gen 2 stuff you could eliminate the cat and use a spacer on the rear sensor and the computer would never know. the front o2 would adjust the fuel air ratio and the rear one would be tricked into think the cat was doing its job. Edited January 25, 2012 by johnegg Link to comment Share on other sites More sharing options...
whitetiger Posted January 25, 2012 Share Posted January 25, 2012 ^iirc, "bank 0" is the upstream cat, and "bank 1" is down stream Link to comment Share on other sites More sharing options...
nvr-enuf Posted January 25, 2012 Author Share Posted January 25, 2012 So do i spend $60 on a rear O2 sensor or a spacer on the rear which would solve the problem "if" the cat is not doing it's job? A univeral CAT is $70. Is there a way I can test the rear O2 sensor? Link to comment Share on other sites More sharing options...
whitetiger Posted January 26, 2012 Share Posted January 26, 2012 if the cat is not doing its job, then there is a chance it could be on the verge of getting clogged. buy the sensor. most of the time, its the sensor that goes bad. so if thats the case which it it most likley is, the spacer wont do squat. the senor is cheap and easy to install. do that and see. buy the sensor. Link to comment Share on other sites More sharing options...
nvr-enuf Posted January 26, 2012 Author Share Posted January 26, 2012 Ok - rear sensor installed, I will get the code cleared and see if this fixes the code. Thanks Link to comment Share on other sites More sharing options...
sil8ty Posted February 12, 2012 Share Posted February 12, 2012 Hello, just thought I'd let people know I'm new here, but I've been struggling with this problem for a few months, replaced the o2 sensors already w/ Subaru parts, error still shows after abit of driving. After I changed the spark plugs, the error stopped coming back. Looking at the spark plugs I noticed that it was under alot of heat, it was all whitish colored. the Electrode also showed signs that the gap changed as compared to the new spark plugs. CAr was about 145,000Km, H6 outback 2005. problem showed around 142,000km. All good, 150,000km as of this post. Link to comment Share on other sites More sharing options...
ehsnils Posted February 13, 2012 Share Posted February 13, 2012 Was all plugs the same color or was it only one? Pictures of old plugs are always interesting. Link to comment Share on other sites More sharing options...
nvr-enuf Posted February 13, 2012 Author Share Posted February 13, 2012 For my issue, i replaced the rear O2 sensor and no more check engine light! Yeah! Link to comment Share on other sites More sharing options...
octain11 Posted February 13, 2012 Share Posted February 13, 2012 i had the same problem happen to me a couple of days ago, after i installed boral UEL headers, the headers where producing more power and heat thus the 02 sensor was confused to sh*t (they are brand new sensors) i put in a spacer and no cel light, exhaust cel are not a huge deal the car is not gunna stop working, you just wont pass inspection, if i were you i would get a spacer rather and see if that works rather than spending 80 bucks on a 02 sensor Link to comment Share on other sites More sharing options...
sil8ty Posted February 14, 2012 Share Posted February 14, 2012 (edited) All of my spark plugs were running too hot, I guess the Passenger side was just worst. The higher heat also meant the car was running closer to lean. The plugs were from the factory and this was the first time they were changed. I'll add a picture later tonight And here they are, sorry I couldn't get a side shot, it's more obvious that the leads bent in because of the heat when compared to a new plug. I also realize I need a micro lens on my camera. Edited February 19, 2012 by sil8ty added the pics Link to comment Share on other sites More sharing options...
octain11 Posted February 14, 2012 Share Posted February 14, 2012 spark plugs wont affect the engine to overheat its very rare especially if you just got new ones, check the voltage of the spark plugs should be between 40,000 to 100,000 volts,i would do a coolant flush and add the subaru coolant conditioner, it can be that simple, check the coolant it should be a nice green, if its grimy green its no good ,did u change the spark plug wires as well? if you didnt that can also be the problem, your car has a lot of mileage on it, i had to do the same when i was at 150k, change all sparks and wires, but the car never overheated Link to comment Share on other sites More sharing options...
sil8ty Posted February 15, 2012 Share Posted February 15, 2012 No, I'm not saying the engine is overheating, the car is running leaner than normal causing a my cel p0420 fault, it's clear now, and I did do a coolant flush at the dealer recently too. Would have done the flush myself, but they say it's a flush, not just a drain and replace. Link to comment Share on other sites More sharing options...
octain11 Posted February 15, 2012 Share Posted February 15, 2012 ya flush is nt too hard on our cars, they offered me a flush as well, it was 170 i rejected his offer before he finished the sentence, there is a drain plug on the bottom of the radiator, you unplug and it will leek out, after its all out pour water in the reservoir until the water comes out clean, after that you poor in your coolant and subaru conditioner, then start the car with the heater on full blast and let the car idle w/ the rad. cap off. Keep adding fluid until the air bubbles are out. I let mine idle until it gets up to temp. You might also have to squeeze the upper rad. hose while it's idling to get all of the air bubbles out. Link to comment Share on other sites More sharing options...
sil8ty Posted February 16, 2012 Share Posted February 16, 2012 No, that's a drain, a flush should be done with a machine which circulates new coolant into the system while removing the old coolant at the same time. The major advantage is you should be able to monitor the old coolant till it's all be replaced and that it is free of contamination/sediment. Though there really shouldn't be any crap/rust in there. Link to comment Share on other sites More sharing options...
Shawnd1980 Posted February 16, 2012 Share Posted February 16, 2012 For my issue, i replaced the rear O2 sensor and no more check engine light! Yeah! I recently got the two codes when having my car scanned. I got the P0420 code as well as P0020. To fix the P0420 I will check fixing that code with an Oxygen Sensor. Im not sure what it will take to fix the P0020 code, I have to research that more. Did your cruise control light flash while your check engine light was on?? Link to comment Share on other sites More sharing options...
octain11 Posted February 16, 2012 Share Posted February 16, 2012 No, that's a drain, a flush should be done with a machine which circulates new coolant into the system while removing the old coolant at the same time. The major advantage is you should be able to monitor the old coolant till it's all be replaced and that it is free of contamination/sediment. Though there really shouldn't be any crap/rust in there. they are pretty much the same, the machine way just drains it completely then fills it with water and drains, then coolant. the other way of flushing is just a cheaper DIY flush, which honestly there isnt going to be a big difference, i have done both at subaru dealer which was about $180, and did myself which cost me about $35 including the subaru conditioner. .you just keep on adding water to the radiator until it comes out clean, just like the machine does but not as fast. the car performed the same, and when you do it yourself you can actually use quality coolant which most places use the cheap stuff Link to comment Share on other sites More sharing options...
octain11 Posted February 16, 2012 Share Posted February 16, 2012 To fix the P0420 I will check fixing that code with an Oxygen Sensor. Im not sure what it will take to fix the P0020 code, I have to research that more. Did your cruise control light flash while your check engine light was on?? P0420 is not a big deal, its probably a bad 02 sensor if you have a stock exhaust, and you still have the factory sensors, P0020 means there is something wrong with the variable valve timing components and the power train. i would get that checked out or ask someone experienced i dont too much about that fix Link to comment Share on other sites More sharing options...
sil8ty Posted February 17, 2012 Share Posted February 17, 2012 My cruise started blinking and the cel stayed lit when the p0420 tripped. Link to comment Share on other sites More sharing options...
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