P0420 "Catalyst System Efficiency Below
Thread Starter
Instructor
Joined: Feb 2005
Posts: 242
Likes: 2
From: Mims Florida
P0420 "Catalyst System Efficiency Below
I have gotten a P0420 "Catalyst System Efficiency Below Threshold " trouble code. I installed long tube headers with after market cats about two thousand miles ago. How common is this code and does it really mean my cat is going bad?
Race Director
Joined: Jul 2004
Posts: 16,795
Likes: 62
From: Lake Havasu City, AZ
no it is one of the standard codes one can get with headers... and high flow cats....
the exhaust gases hit the rear o2 sensors at a different time ( due to different flow rate thruought the headers and high flow cats)and it throws a code.....
the exhaust gases hit the rear o2 sensors at a different time ( due to different flow rate thruought the headers and high flow cats)and it throws a code.....
Pro
Joined: Mar 2004
Posts: 653
Likes: 0
Or the wiring to the rear O2 sensor got melted, it happens with aftermarket headers when the wires route too close to the exhaust. Get under there and inspect the wiring to the rear O2 sensors on both sides very closely.
Thread Starter
Instructor
Joined: Feb 2005
Posts: 242
Likes: 2
From: Mims Florida
P0420 code
Thanks, I cleared the code for now as it was listed as an H ( Historical ) I will get into it more if it comes back. It is the first code I have had after doing heads, cam, and headers. It appears to be pretty common with headers as far as other posts go.
Team Owner
Joined: Jan 2004
Posts: 22,185
Likes: 65
From: NJ
Did you get a a tune after the heads/cam? The tuner should have turned that code off. High flow cats are not as efficient as OE cats, in fact they are largely ineffective, and this code will be very common.
A good tuner will set the car up correctly.
