P0420/P0430 Codes...Fuel issue?
Thread Starter
On The Tree
Joined: Aug 2002
Posts: 165
Likes: 0
From: St. Louis, MO
P0420/P0430 Codes...Fuel issue? The county I live in mandates gasoline with 10% Ethanol content (for lower emissions they claim 
). Whenever I fill up locally, I get an SES light and P0420, and P0430 codes along with increased detonation. So I usually fill up near where I work (different county, no Ethanol in fuel) and I get no codes and the car runs great. Well, now that county also requires the Alky-blend, so I have to burn the 10% Ethanol fuel. Is anyone else having this problem? I plan to install O2 sims to solve the SES light issue, but would like to hear other opinions. Thanks.
-Nate
). Whenever I fill up locally, I get an SES light and P0420, and P0430 codes along with increased detonation. So I usually fill up near where I work (different county, no Ethanol in fuel) and I get no codes and the car runs great. Well, now that county also requires the Alky-blend, so I have to burn the 10% Ethanol fuel. Is anyone else having this problem? I plan to install O2 sims to solve the SES light issue, but would like to hear other opinions. Thanks.-Nate
TECH Apprentice
Joined: Jan 2002
Posts: 332
Likes: 0
From: Louisville, KY
Not sure of the reason but those codes are for "inefficient Cats". I have a friend with the same codes that keep coming up. Her front O2's read low, while the rear O2's seem to read normal. Of course with the front O2's reading low and the rear reading normal, the computer thinks the cats are inefficient and thus the codes. The car runs great. We can't figure out WHY the front O2's are reading so low. We swapped out for an O2 we knew worked and got the same result.
If anyone has any ideas of this problem too, it would be appreciated.
If anyone has any ideas of this problem too, it would be appreciated.
Teching In
Joined: Dec 2003
Posts: 5
Likes: 0
I'm getting the 0420 code since installing cam, headers, and hi flow cats but not the 0430. A friend with EFI reset the light last Wed but it came back on Sun, The car is still running on the stock tune, could that have anything to do with it? 
