Code P0420? What would cause this?
Thread Starter
Race Director
Joined: Apr 2004
Posts: 16,135
Likes: 5
From: Newberry FL
Cruise-In VIII Veteran
St. Jude Donor '07
Code P0420? What would cause this?
I finally got the car running well, added:
BORLA XR-1 Racing System
Random Tech High Flow Cats
B&B Shorty headers
LS6 Intake Manifold
New plugs (ACDelco Iridiums)
New wires (MSD SC 8.5)
The car is running like a champ, but this code (P0420) came up and I am not sure why.
Thanks and man these mods added some nice gains!
Micah
BORLA XR-1 Racing System
Random Tech High Flow Cats
B&B Shorty headers
LS6 Intake Manifold
New plugs (ACDelco Iridiums)
New wires (MSD SC 8.5)
The car is running like a champ, but this code (P0420) came up and I am not sure why.
Thanks and man these mods added some nice gains!
Micah
Burning Brakes
Joined: Feb 2000
Posts: 1,247
Likes: 0
From: Denver CO
I have been getting an occasional 420 code; I don;t remember the exact wording but it has something to do with left bank exhaust (is it one of the O2 censors, after the cats). In my case I figured the FI was eating the cats. I haven't been worrying about it. Sometimes I also get the 430 code.
Race Director
Joined: Oct 2002
Posts: 16,477
Likes: 26
From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
It's likely due to the high flow cats.
This TWC system (three way catalyst) code happens when there is insufficient difference in readings between the front and rear 02 sensor. This code exists basically to tell you your catalytic converter has lost it's efficiency. So, altering the stock cats can and will alter the sensor differential readings, and possibly set off this code (or P0430..same thing, just the right side exhaust).
I would reset it and see if it happens again. You may also get the P0430 code too. If it continues to be a problem, the surefire way to cure it would be to disconnect the rear 02 sensors and run sims instead.
This TWC system (three way catalyst) code happens when there is insufficient difference in readings between the front and rear 02 sensor. This code exists basically to tell you your catalytic converter has lost it's efficiency. So, altering the stock cats can and will alter the sensor differential readings, and possibly set off this code (or P0430..same thing, just the right side exhaust).
I would reset it and see if it happens again. You may also get the P0430 code too. If it continues to be a problem, the surefire way to cure it would be to disconnect the rear 02 sensors and run sims instead.
Thread Starter
Race Director
Joined: Apr 2004
Posts: 16,135
Likes: 5
From: Newberry FL
Cruise-In VIII Veteran
St. Jude Donor '07
Originally Posted by Y2Kvert4me
It's likely due to the high flow cats.
This TWC system (three way catalyst) code happens when there is insufficient difference in readings between the front and rear 02 sensor. This code exists basically to tell you your catalytic converter has lost it's efficiency. So, altering the stock cats can and will alter the sensor differential readings, and possibly set off this code (or P0430..same thing, just the right side exhaust).
I would reset it and see if it happens again. You may also get the P0430 code too. If it continues to be a problem, the surefire way to cure it would be to disconnect the rear 02 sensors and run sims instead.
This TWC system (three way catalyst) code happens when there is insufficient difference in readings between the front and rear 02 sensor. This code exists basically to tell you your catalytic converter has lost it's efficiency. So, altering the stock cats can and will alter the sensor differential readings, and possibly set off this code (or P0430..same thing, just the right side exhaust).
I would reset it and see if it happens again. You may also get the P0430 code too. If it continues to be a problem, the surefire way to cure it would be to disconnect the rear 02 sensors and run sims instead.
Thanks and see on the roads!
Burning Brakes
Joined: Oct 2001
Posts: 1,116
Likes: 0
From: Alhambra Calismognazifornia, in the country everyone comes just to complain but won't go back home!
since installing my RT cats and x-pipe i get both these codes about once a month....oh well, i just reset them and move on 
Team Owner
Joined: Apr 2001
Posts: 54,204
Likes: 180
From: S.W. Ohio. . . . . . NRA Life Member
Originally Posted by Y2Kvert4me
It's likely due to the high flow cats.
This TWC system (three way catalyst) code happens when there is insufficient difference in readings between the front and rear 02 sensor. This code exists basically to tell you your catalytic converter has lost it's efficiency. So, altering the stock cats can and will alter the sensor differential readings, and possibly set off this code (or P0430..same thing, just the right side exhaust).
I would reset it and see if it happens again. You may also get the P0430 code too. If it continues to be a problem, the surefire way to cure it would be to disconnect the rear 02 sensors and run sims instead.
This TWC system (three way catalyst) code happens when there is insufficient difference in readings between the front and rear 02 sensor. This code exists basically to tell you your catalytic converter has lost it's efficiency. So, altering the stock cats can and will alter the sensor differential readings, and possibly set off this code (or P0430..same thing, just the right side exhaust).
I would reset it and see if it happens again. You may also get the P0430 code too. If it continues to be a problem, the surefire way to cure it would be to disconnect the rear 02 sensors and run sims instead.
Race Director
Joined: Jun 2004
Posts: 19,459
Likes: 48
From: Schaumburg IL
CI 7-8-9-11 Veteran
St. Jude Donor '06-'10, '13
Originally Posted by Y2Kvert4me
It's likely due to the high flow cats.
This TWC system (three way catalyst) code happens when there is insufficient difference in readings between the front and rear 02 sensor. This code exists basically to tell you your catalytic converter has lost it's efficiency. So, altering the stock cats can and will alter the sensor differential readings, and possibly set off this code (or P0430..same thing, just the right side exhaust).
I would reset it and see if it happens again. You may also get the P0430 code too. If it continues to be a problem, the surefire way to cure it would be to disconnect the rear 02 sensors and run sims instead.
This TWC system (three way catalyst) code happens when there is insufficient difference in readings between the front and rear 02 sensor. This code exists basically to tell you your catalytic converter has lost it's efficiency. So, altering the stock cats can and will alter the sensor differential readings, and possibly set off this code (or P0430..same thing, just the right side exhaust).
I would reset it and see if it happens again. You may also get the P0430 code too. If it continues to be a problem, the surefire way to cure it would be to disconnect the rear 02 sensors and run sims instead.
Exactly right 
I had , and have the same code on mine and am running high flow cats. I will eventually get the LS1 edit, or buy O2sims..I want to wait on the LS1 edit until I can get a cam package install so I get more for the buck...unless of course I get my emissions notice before that 
Thread Starter
Race Director
Joined: Apr 2004
Posts: 16,135
Likes: 5
From: Newberry FL
Cruise-In VIII Veteran
St. Jude Donor '07
Originally Posted by FrankTank
Exactly right I had , and have the same code on mine and am running high flow cats. I will eventually get the LS1 edit, or buy O2sims..I want to wait on the LS1 edit until I can get a cam package install so I get more for the buck...unless of course I get my emissions notice before that Like this guys thinking, you must have been reading my mind! LOL!
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