Damn SES light-Need help
 

I have had a Code P0420 (Catalyst Sys efficiency Theshold ((Bank 1)) for about 2 months. I had this before and after the Header install. I changed both Pre-cat O2 Sensors and still same thing. What can it be. Any help I would really appreciate it.

Do you still have cats and post-cat o2 sensors? If yes, then your bank 1 (driver side) cat is bad or your driver side post-cat o2 sensor is bad.
If you do not have cats but you still have rear o2 sensors, then the code is to be expected, but you should be getting codes for both banks. Now if you have no cats and no rear o2 sensors and you are not running o2 sims, then you should be getting a Bank 1 Sensor 2 and Bank 2 Sensor 2 o2 circuit malfunction codes.

I have Shorty headers. I have Pre and Post Sensors. Im going to change the post Cat then and see what happens. Think they are the Original Sensors. I never changed them until now. Cats are only a year old.

Ill give that a try and see what happens. Thanks a lot. keep yall posted

Cat is bad. Are they OE cats?

Random tech cats

do you have a scanner? if so you can monitor post and pre cat o2 sensors. well the post cat o2 sensors shouldnt really be switching, they will but slightly. if your post cats are switching as irratic as youre precat sensors then youre cat isnt filtering anything out and needs to be replaced.

I used a Snap-On scanner and was monitoring Bank 1 and 2. pre cat sensors were going crazy all over the place. Both post were stable.

Well found a fix for this. After research I found out that due to the High flow cats and headers to much Fumes were going thru so it was throwing a code. I bought these Defoulers and drilled them out and added them to the post cat sensors and no more codes. All it does is take the sensor out of the direct path of the gasses. GREAT fix.

http://img.photobucket.com/albums/v3...e/photo2-4.jpg
http://img.photobucket.com/albums/v3...e/photo1-3.jpg

If I would of knows they were high flow cats I could of told u. But I didn't know haha. Yeah it usually sets when it fluctuates at the same rate as the front O2. The rear O2 is thinking the cat is bad.