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Old 05-09-2012, 04:35 PM   #1
teefivetee
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Member#: 296046
Join Date: Sep 2011
Vehicle:
2005 sti

Default p0420 only when its hot out?

Hey guys, ill keep this quick. Randomly when the weather gets warmer here, my car will throw this code from time to time and then go away. Anything to worry about ? Cat runs like a champ otherwise

Thanks in advance
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Old 05-09-2012, 07:38 PM   #2
silverstreak02
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Location: Kannapolis, NC
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Hmm..usually a catalyst code isn't altered too much by weather.

Mods?

Could be an 02 sensor that's become lazy over time and isn't switching as need be.
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Old 05-09-2012, 07:46 PM   #3
teefivetee
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It's weird, came.with custom exhaust and downpipe. Intake. That's about it. No cat, but my buddy did the defouler trick to make the Cel turn off. Wouldn't the car run funny or have a decrease in mpg if the o2 crapped out ?

But totally random. Usually goes away next day
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Old 05-09-2012, 07:51 PM   #4
silverstreak02
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I have a P0420 that comes and goes as well. My fuel economy is still 28-33 mpg even when the code is active. The previous owner put in an aftermarket 02 that doesn't switch as properly as an OEM sensor, so it creates a cat code even though the cat is good.

So to answer your question, it CAN alter your fuel economy, but not always because the fuel trims are still based on the sensor whether it's slow or not. Also, not entirely sure about Subarus but my experience as a tech with Hyundai/Kia has me familiar with the vehicle resetting to a default in order to protect the converter from raw fuel damaging it.
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Old 05-09-2012, 07:52 PM   #5
teefivetee
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I'm so stupid. The code is p0442. My bad
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Old 05-09-2012, 07:57 PM   #6
silverstreak02
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http://forums.nasioc.com/forums/show....php?t=1888770

This thread may help. I had this problem one day as well, only my valve was actually broken where the hose connects to it. Hopefully this will fix your situation
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Old 05-09-2012, 09:04 PM   #7
scarney1988
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As with any evap code, especially an intermittent one, I'de recommend replacing your gas cap with an OEM. Clear the code, and test drive. If code returns, and cap is tight. Come back and post the code and freeze frame data.

Good luck
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