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Old 02-06-2011, 02:09 AM   #1
Sir-Knight
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Member#: 73636
Join Date: Nov 2004
Chapter/Region: E. Canada
Location: the 'wa, ontario, canada
Vehicle:
2007 Impreza 2.5i SE
newport blue pearl

Default p0420

bugger. Started up the car, went out to clean the snow off it, but as I got in I slipped on my floor liner and foot hit the gas, revving the piss out of the engine before the cat was hot, threw the code about 10 minutes later on the way home. First time I've seen this code after a year with the brullen exhaust, the other code from last year was a bad front o2 sensor, replaced the sensor last april/may and have not had an issue since.

is 420 truly indicative of the front o2 dying again or is it just because I flooded the cat with an ultra rich mix before it was hot?
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Old 02-07-2011, 09:44 AM   #2
Boxer4Dad
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Join Date: Jan 2007
Chapter/Region: MWSOC
Location: SE Michigan
Vehicle:
2005 Saabaru 2.5i
OBP, or Black

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Hard to say from far away.

I vote for #2, and that an ECU reset will make everything happy again. Try it before buying a new O2 for sure.

BTW, I hate driving with winter boots, too. Stuff like that just happens...
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Old 02-07-2011, 10:33 AM   #3
kero
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Due to my uel's, I had to have a local tuner remove that dtc from my ecu since I have no cats with my setup.
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Old 02-07-2011, 11:02 AM   #4
rallyvovo
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Had the same code come on a week ago, cleared it and hasnt popped back up....would this usually mean all is well and something fluky happened like your situation?
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Old 02-07-2011, 12:43 PM   #5
kero
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SRP

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If the code went off, it's still most likely stored in the ECU, if you reset the ECU it will come up again once the right mileage or conditions are met for the ECU to recheck for that DTC, that is, if there is an issue that is ongoing.

I had not choice but to have it removed from my ECU via local tuner since I couldn't pass inspection. Plus without cats, I would get it again once I cleared the ECU and it met the right criteria to recheck the conditions for that DTC.
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Old 02-07-2011, 05:37 PM   #6
Sir-Knight
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2007 Impreza 2.5i SE
newport blue pearl

Default

well the old brullen wasn't designed for the 07, so the cat location moved from the bottom of the rad all the way to midway past the front doors, so I figure it's a bit of a ways from the ports and immediate hottness of the engine so it would take a bit longer to warm up.

I have a feeling my first front o2 went out like this last year when I hot lapped an autox course with the cold cat. but I think that code was p0131. This is the first time I've seen this code with this exhaust on the car, and it's been on for about a year now through track days and autox.

It happened saturday night, it's now monday, I cleared the code with my reader and the ecu spent a few start cycles and drives to relearn, it seems to be back to normal, took it out on the highway properly at temp and brought it up to about 4.5k and no light, drove around usnday for a couple hours around town, and did this morning's short commute and no light, so maybe it was just the cold cat with super rich mix from when my foot slid onto the gas.
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Old 02-07-2011, 08:52 PM   #7
kero
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^^ Some DTC's will require more than a few hours of mixed driving and restarts before it checks for the same condition again. Could be quite a bit of mileage, my 1st P0420 after clearing the ECU took almost 200 miles to come back up, again it depends on the driving conditions, etc etc.
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