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Old 06-22-2007, 05:41 PM   #1
wrxpilot44
Scooby Newbie
 
Member#: 152125
Join Date: Jun 2007
Chapter/Region: TXIC
Location: Houston, TX
Vehicle:
2004 WRX
Blue

Question P0420 Code comes on when fuel tank is low?

Well I was just wonderin if anyone had any ideas on whats happening here. When my fuel tank gets low (right about when the low fuel light comes on) my CEL comes on also. Then after I fill up and drive for about 30 mi on the new tank the light goes out. I thought it might have been bad gas until it happened again when I got low on fuel again.

So far its happened 3 times in a row, so I went and got the code read and its a P0420 - Catalyst efficiency below threshold, which is apparently an emissions problem.

Now I cant figure out why it only comes on when the tank is low on fuel and what the problem could actually be. The only thing I can think of is that maybe the tank has some sort of contaminants that are just sitting at the bottom of it.

Anyone out there have any ideas??? Any help is greatly appreciated.
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Old 06-22-2007, 08:12 PM   #2
surowrxa
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Member#: 102895
Join Date: Dec 2005
Chapter/Region: MAIC
Location: Pittsburgh
Vehicle:
'12 Forester
'17 Outback

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440 would be the code for the gas tank/evap system. Low fuel (and a leak somewhere) may cause a change/loss in vacuum resulting in code, but...if it really is the dreaded 420, and you drive a WRX (fill out your profile or tell the people what you drive, mods, etc.), then it probably has to do more with your O2 sensors/cat converters then your evap system. People usually get the PO420 when they delete a cat or two, or their O2 sensor is going south.
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Old 06-22-2007, 11:00 PM   #3
Jon [in CT]
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Join Date: Nov 2000
Chapter/Region: NESIC
Location: Connecticut, USA
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02 WRX Sedan
Silver

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Although some trouble codes' detection criteria include fuel tank level, P0420 detection is independent of how much gas is in the tank. Probably a coincidence.
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