timintc Posted June 17, 2007 Share Posted June 17, 2007 after dealing with the 420 code on and off for a couple years i decided to finally have the O2 sensors changed on my 2000 legacy with 125K on the odo. after about a week the code came back so the shop took the exhaust system apart and blew out the cats and reset the O2 sensors. before another week went by the CEL came back on again, this time he swapped my cats for some that he had gotten off a salvaged legacy with under 7K, the sensors are denso and now with nearly new cats the CEL came back on again , his recommendation is that he has done all he can do, and to just take it to the subaru dealer and have the code erased from the computer, anyone with any ideas or like experiences on this one???? Quote Link to comment Share on other sites More sharing options...
porcupine73 Posted June 17, 2007 Share Posted June 17, 2007 Are they sure there are no leaks in the exhaust system before or shortly after the sensors? Even a small pinhole leak or slightly leaky gasket can cause an issue. The other thing would be use a brand new OEM sensor for the front. I'm not sure if that's what you have. Quote Link to comment Share on other sites More sharing options...
nipper Posted June 18, 2007 Share Posted June 18, 2007 The front sensor really needs to be a Subaru sensor. This has been known to cause a 420 code. nipper Quote Link to comment Share on other sites More sharing options...
OB99W Posted June 18, 2007 Share Posted June 18, 2007 [...]his recommendation is that he has done all he can do, and to just take it to the subaru dealer and have the code erased from the computer[...]Excuse me, but what is that supposed to accomplish? See this article for a bit more insight: http://www.motor.com/MAGAZINE/Pdf/102006_09.pdf Quote Link to comment Share on other sites More sharing options...
nipper Posted June 18, 2007 Share Posted June 18, 2007 Excuse me, but what is that supposed to accomplish? See this article for a bit more insight: http://www.motor.com/MAGAZINE/Pdf/102006_09.pdf Man i need to find those owners who absoloutly beleive the ECU/CEL light on their cars (in reference to the cat). i have a nice bridge in brooklyn to sell them.... nipper Quote Link to comment Share on other sites More sharing options...
xrturbo Posted June 19, 2007 Share Posted June 19, 2007 Are you close to the guy that works on it for you? All shops play the game of the miraculous ultra low mileage part that they got. The way it works at most places that source used parts is they buy it from some yard with a car that has 120,xxx miles, they sell it to the shop telling them it only has 40,xxx miles and then they sell it to you with 7000 miles. The parameters for these O2s especially the planar type found in the 00 and up models have such tight tolerences that the slightest "insufficency" found will throw the light for 420. At my shop we do these cats all the time. I know I am gonna catch hell for saying that but it is the truth. No offense it is a pricey fix and everyone wants to find a way to say it isn't the cat, but if we tried everything else before replacing the cat we would loose so much labor time it would be insane. 98% of the time we get the 420 code and put a new or 100% known working used one on the light is gone for good. Just had an 02 OB 5spd and an 03 forester this week for it. Quote Link to comment Share on other sites More sharing options...
OB99W Posted June 20, 2007 Share Posted June 20, 2007 [...] The parameters for these O2s especially the planar type found in the 00 and up models have such tight tolerences that the slightest "insufficency" found will throw the light for 420. At my shop we do these cats all the time. I know I am gonna catch hell for saying that but it is the truth. No offense it is a pricey fix and everyone wants to find a way to say it isn't the cat, but if we tried everything else before replacing the cat we would loose so much labor time it would be insane. With careful diagnosis, it's usually possible to determine whether it's the cat or O2 sensor alone causing the code, or a bad O2 sensor that also killed the cat. If both have high mileage, it could certainly be either or both. In a shop, it doesn't "pay" to hang a lot of parts if replacing one will clear the code. However, if an owner can provide the labor, changing an oxygen sensor that has a lot of miles on it will probably not be a waste of money; if it doesn't cure the P0420, it might just provide better gas mileage, or help keep a new cat (if needed) healthy. 98% of the time we get the 420 code and put a new or 100% known working used one on the light is gone for good. Just had an 02 OB 5spd and an 03 forester this week for it.How long is "for good", and are you also replacing oxygen sensors or at least testing them for proper response? Hanging a new cat might get rid of the code, but if the sensor is marginal, the new cat might not have "nine lives". Quote Link to comment Share on other sites More sharing options...
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