This forum is a first for me. I need help attmepting to correct a trouble code i have been getting. P0420, it says something about "PCM has determined that the catalyst system efficiency for bank 1 is below threshold." I need help, i have true duals with Flowmaster 20 series 3 chamber mufflers, 3" high flow cats, a hypertech programmer and a K&N cold air intake. Any ideas? my email is tennesseebadassmofo4u@yahoo.com

 

O2 sensor 1/1.

That is the one in front of the cat on the pass side unless you only have one cat. Then its the one in front of the cat.

If you don't have any exhaust leaks and the cat is physically damaged, then its probably the sensor itself.

You don't say the year of your truck so I can't be more specific.

 

I went ahead and replaced all4 O2 sensors, god only knows whent he last time these things were replaced. However, i still have these fault codes come up. Not so much for bank 2, but bank 1 gives me the same P0420 trouble code. Any one got any ideas???[X(]