Downpipe/CEL/spark plug fix question

I have an 08 GT and I put an Invidia catless downpipe on and the CEL came on for a couple hundred miles and then turned off but I went ahead and did the spark plug defouler thing and I used both defoulers. Recently I got a CEL again and it is P2096 and P0420. What am I doing wrong here? I am trying to get rid of these CELs.

You will need some sort of engine management, normally when you are able to shut off one code via the CEL Fix, the other code comes on.

Did you clear the P0420 when the CEL came on the first time?

It's extremely unusual to get both the P0420 and P2096 at the same time.

Clear both CELs using an OBDII scanner and then remove one of the defoulers (use only one).

I havent cleared any code. It went away on its own the first time. I dont have an OBDII scanner, is there any other way to clear it?

The light will go out but the code remains in the ecu.

You can borrow a OBDII scanner from your local auto parts store for free. That's what I used to do until I bought one on sale for $30.

The 07 and 08 are CAN so you need to use a newer OBDII scanner that is CAN compatible.

Is it bad to drive around for a while without doing that?

I'm not familiar with how the '08 deals with rear O2 sensor failures.

Sometimes, if the ecu thinks the rear O2 has failed or is missing, the engine will change the settings to run rich ... all the time.

I would clear it and take one of the defoulers out. All it takes is a trip to the auto parts store.

My CEL just turned off by itself again. I'm not really sure what's going on.

You will not do any harm. The rear O2 sensor is there just for emissions purposes, it does nothing to adjust AFR.

Since search works...

I want to go catless, run stage 2 and ensure no cell or ECU code. I have a Cobb AP. Will I need to run this defouler and will it prevent a code?