I put my wait for me tune in about 3 weeks ago, I had the SES light on with my factory ECM, because I had removed the cats, when I put the new ECM in the SES light was not on, well last week guess what came back on. SERVICE ENGINE SOON!!! I took the truck to Advance Auto to get the code read and it said P0420, Catalyst Efficiency below threshold Bank 1, Basically Jesse did not turn off the rear O2 sensors as I requested, or this thing is running so rich it is setting off a code from the front 02's. Does anyone know for sure if the P0420 code is from the rear 02's??? Thanks for the help, I am going to try to get ahold of Jesse to see if I can get another Tune.

 

Check this out: OBD-II codes website

 

The PCM uses the rear O2's for that code...