for the last couple of days ive been getting the cel code P0420: P0420 Catalyst System Efficiency Below Threshold (Bank 1)


these are the solutions ie seen from different sites.

1.) The catalyst in the catalytic converter is cracked, clogged, or otherwise damaged.
2.) The secondary O2 sensor is malfunctioning.
3.) There is an exhaust leak.
4.) The computer unit is faulty.
5.) Clogged EGR Port

would anybody know what typically is the issue is?

 

" '01 Melbourne Red Metallic (M3 Red) CL-S: Comptech Supercharger w/HBP, TL Lip Kit, XS Headers, RT High Flow Cat, HKS Superdragers, Custom Intake, UR Crank Pulley, Sarona Roof Spoiler, OEM M5 Lip Spoiler, 10K HID's, '03 Tails, '03 Fog Inserts, '03 Grille, '03 Headlights, R1 Concept Drilled/Slotted Rotors, Ingalls Front/Rear Camber Kit, Omni Power Coilovers, 20% Tint, Eibach Rear Sway Bar, Tranny Cooler, '07 TL Transmission Apr '10 Work vs-xx "

u have a high flow cat and headers, check the O2 sensors would be my guess

 

It's the high flow cat. Mine sets a P0420 code all the time because the o2 sensor senses much more air coming through as opposed to the stock cat. Best thing to do would be a defouler for the o2 sensor and that should keep the light off. I've just been too lazy to do it yet.

 

^lol right before I read your post I was just reading up on the defouler trick. I'm heading to autozone right now to pick one up.

 

happens to me as well. ever since i got my full exhaust i get the code intermittently.

im on the stock cat. but its shortened to increase velocity

 

I bought an o2 defouler from excelerate when i got the cat. No issues since then for me.