johnd911 Posted October 26, 2011 Share Posted October 26, 2011 I drive 1000 miles a week and am sick of these CEL codes, I have used the plug antifouler fix for years with no problem, now it doesn't work anymore, about 70k on the current sensor. Is it the sensor that finally bit the dust or should I try the electronic fix, which I can't find anymore anywhere. I have a 2001 Outback Auto, Help, inspection due in a few months. If I have to replace the sensor, do I HAVE to get an OEM ($$) one. Thanks people. Quote Link to comment Share on other sites More sharing options...
johnd911 Posted October 26, 2011 Author Share Posted October 26, 2011 it's the 420 code for the rear sensor. Quote Link to comment Share on other sites More sharing options...
johnceggleston Posted October 26, 2011 Share Posted October 26, 2011 how many miles on the car? you put the anti-fouler on the rear. have replace either o2 sensor before? if so at what mileage and how many miles ago? what prompted the anti-fouler? Quote Link to comment Share on other sites More sharing options...
johnd911 Posted October 26, 2011 Author Share Posted October 26, 2011 291,000. Engine was rebuilt at 219,000 due to a disintegrated crank bearing. The antifoulers got rid of the 420 code every single time it appeared. The rust out, so I replace them everytime the code comes back. This car gets the best care because it is my personal and work car. Last sensor was put in 40,000 miles ago, Subaru part. Quote Link to comment Share on other sites More sharing options...
johnd911 Posted October 26, 2011 Author Share Posted October 26, 2011 Cats have been replace 3 times already, just put in a cheap Knock sensor, and all of a suddent eh 420 code pops up and the antifoulers don't get rid of it anymore, coincidence? The fouler things work great, have been using them for years, just been replacing them everytime the code pops up. Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 26, 2011 Share Posted October 26, 2011 Replace both sensors with NTK brand units. GD Quote Link to comment Share on other sites More sharing options...
johnd911 Posted October 26, 2011 Author Share Posted October 26, 2011 best source for them? thanks Quote Link to comment Share on other sites More sharing options...
jarl Posted October 26, 2011 Share Posted October 26, 2011 There's an excellent thread at NASIOC about a guy diagnosing his P0420 with the help of a Subaru technician: http://forums.nasioc.com/forums/showthread.php?t=2210139&highlight=oxygen&page=3 I don't know if you have the tools to diagnose this, but even taking the car to a dealer to have it diagnosed sounds like a sensible alternative... Quote Link to comment Share on other sites More sharing options...
ocei77 Posted October 26, 2011 Share Posted October 26, 2011 Replace both sensors with NTK brand units. GD or Bosch. O. Quote Link to comment Share on other sites More sharing options...
NorthernAQS Posted October 26, 2011 Share Posted October 26, 2011 I just dealt with the P0420 issue on my 2000 OBW successfully. My car has the equivalent of 130,000 miles on it (bought at 125,000) and came with aftermarket cats/Bosal brand exhaust. My code was persistent and came back every 3-400 miles. I was advised that many P0420 catalyst efficiency below threshold codes are caused by an exhaust leak upstream of the second 02 sensor. I listened for a leak and couldn't hear anything. I replaced the PCV. I replaced the O2's. The code still came back. I used ether on the vacuum lines to test for a leak, nothing found. Finally, I used Seafoam for the significant amount of smoke it produces to test for exhaust leaks. With the car up on ramps, I added a small amount of seafoam to the vacuum line at the brake booster and watched underneath. The smoke revealed a very small leak in the front passenger side corner of the cat, adjacent to the front 02 sensor. It was such a small leak, I couldn't hear it, I thought that it couldn't possibly be the source of my P0420 code. Nevertheless, I welded the seam where the leak was, tested it with more seafoam to verify the leak was sealed, cleared the code and have not have a return in the last 2 tank fulls. I'm by no means a fan of seafoam for its cleaning ability (it spends far too little time in the combustion chamber to be effective in my opinion), but it is invaluable for testing in this capacity. For the cost of visually verifying the absence of exhaust leaks in this manner, I would highly recommend this $8 test prior to throwing any parts at it, like I did. Quote Link to comment Share on other sites More sharing options...
johnd911 Posted October 27, 2011 Author Share Posted October 27, 2011 Dealer is useless, they want to put in Cats. It could be a leak possibly, my hunch is a gone rear sensor. Are there any sensor tests? resistane, etc. in the service manual? or is it just a replace and hope. If it ever get dry here in Buffalo I can do the leak looksee, but have nothing more than a floor jack. Quote Link to comment Share on other sites More sharing options...
johnd911 Posted October 27, 2011 Author Share Posted October 27, 2011 reason I think it may be the sensor ($100 gamble) is the code never disappears, the CEL is always on. None of this off again and back on stuff, just on all the time. Quote Link to comment Share on other sites More sharing options...
jarl Posted October 27, 2011 Share Posted October 27, 2011 I would be interested in a description of the (electrical) tests as well, but the link I posted has an excellent description of how to *really* test both sensors and the converter. You need an OBD2 logger, though (the poster on that thread bought a Tactrix cable, I'm checking to see if I can do something similar with my ebay OBD2 thingie) Check that thread, or if you don't have much time check post #65. Quote Link to comment Share on other sites More sharing options...
Caboobaroo Posted October 27, 2011 Share Posted October 27, 2011 OEM cats? If not, replace them once again with OEM and the sensors as well. I've seen this issue on more Outbacks and Legacys then I can think of. Aftermarket cats can fail as early as 10k miles. Quote Link to comment Share on other sites More sharing options...
johnd911 Posted October 28, 2011 Author Share Posted October 28, 2011 blow over a grand ? on a 300,000 mile car? Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 28, 2011 Share Posted October 28, 2011 Sensors - again use NTK. I don't like the Bosch stuff personally. If that doesn't fix it - put a spark non-fouler between the second sensor and the pipe. That will cure it forever. I agree - don't blow a grand on a 300k vehicle. If it's going to be a problem - throw in a non-fouler and be done with it. Cost is about $8. I do them all the time for people (for off-road use only ) . GD Quote Link to comment Share on other sites More sharing options...
johnd911 Posted October 28, 2011 Author Share Posted October 28, 2011 been using the non foulers for over 60,000 miles with no problem till now, new set didn't help. Light NEVER goes off, gonna try to find the sensor online. Thanks Quote Link to comment Share on other sites More sharing options...
johnd911 Posted October 28, 2011 Author Share Posted October 28, 2011 who has the NTK's? Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 28, 2011 Share Posted October 28, 2011 Amazon. I use www.rockauto.com to get the part number and then buy them off Amazon to avoid the shipping. If the light is always on and the non-fouler is in place - you have bad sensors. GD Quote Link to comment Share on other sites More sharing options...
Caboobaroo Posted October 28, 2011 Share Posted October 28, 2011 The P0420 code is not a sensor code it is a catalyst deficiency code. If you're trying to do it cheap, well I don't think sensors are going to help but you can try. I believe the cats are failing once again and need to be replaced. Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 29, 2011 Share Posted October 29, 2011 The ECU can't always detect sensors that have gone lean or rich. The right combination of bad sensors will throw a 420 code - if the front starts reading lean the ECU will start enriching the mixture - more fuel means more for the cat to deal with and pretty soon you have codes being thrown around. The sensors are cheap and quick to change - they are the first thing to eliminate. You don't throw the most expensive parts at a problem till you rule out the cheap ones. With new sensors you can be SURE that what the ECU is reportiing is correct. And if it still throws codes - then you probably have a leak. GD Quote Link to comment Share on other sites More sharing options...
brus brother Posted October 29, 2011 Share Posted October 29, 2011 (edited) The ECU can't always detect sensors that have gone lean or rich. The right combination of bad sensors will throw a 420 code - if the front starts reading lean the ECU will start enriching the mixture - more fuel means more for the cat to deal with and pretty soon you have codes being thrown around. The sensors are cheap and quick to change - they are the first thing to eliminate. You don't throw the most expensive parts at a problem till you rule out the cheap ones. With new sensors you can be SURE that what the ECU is reportiing is correct. And if it still throws codes - then you probably have a leak. GD GD, Don't mean to hijack post but I've had the 0420 code for a while on my 05 OB. This vehicle has two front (pre-cat) and two rear (post-cat) sensors and one more on the rear cat. I tried the antifouler on the passenger (post-cat) rear sensor without success as it caused a different code to be thrown (2096). I removed the antifouler and installed black tape over dash warning lights. ;-) I haven't gotten around to trying the antifouler on the driver's and passenger post-cat sensor. With 130,000 miles on the car, is it advisable to change out the front sensors as a routine maintenance item or would they have thrown a different code than 420. Hate to waste the $ if they aren't at fault. Also hate to kill the cat. Edited October 29, 2011 by brus brother Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 29, 2011 Share Posted October 29, 2011 Absolutely - over 100k is questionable territory for any O2 sensor. I just replaced both front and rear sensors on a Ford with a "bank 1 lean" code at 156k - problem solved - passed emissions the next week. If you are going to replace sensors - replace them ALL. Fronts and rears. They aren't that expensive and if one is going out or has thrown a code or you suspect it's the cause of a rich condition (0420 code) then the other's can't be far behind it. GD Quote Link to comment Share on other sites More sharing options...
brus brother Posted October 30, 2011 Share Posted October 30, 2011 Absolutely - over 100k is questionable territory for any O2 sensor. I just replaced both front and rear sensors on a Ford with a "bank 1 lean" code at 156k - problem solved - passed emissions the next week. If you are going to replace sensors - replace them ALL. Fronts and rears. They aren't that expensive and if one is going out or has thrown a code or you suspect it's the cause of a rich condition (0420 code) then the other's can't be far behind it. GD 5 sensors total. This will add up to a tidy sum... Would you use only oem on front two precat sensors? What brand if not oem? Also what brand for two postcat sensors and the one that sits on top of the rear cat? Quote Link to comment Share on other sites More sharing options...
jarl Posted October 31, 2011 Share Posted October 31, 2011 (edited) Sorry for the stupid question, but I thought the OEM sensors were Denso. Weren't they? Edited November 1, 2011 by jarl Oopsy... Quote Link to comment Share on other sites More sharing options...
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