I just Bought a 2006 Crew cab Sierra and as soon as I got home the check engine light came on. I went to autozone and this is the code that came up.

P2A04

Was wondering what this was and what is causing it.

Thanks for you help.

The truck has a 5.3L and 72k Miles if that helps.

I will be calling the dealer i bought it from tomorrow just trying to calm my nerves so i can sleep.

 

When it comes to codes. GOOGLE is GOD.

It's an "unknown error" related to the Passenger side (Bank 2) Rear sensor (sensor 2) that monitors your cats to make sure they are working.

Maybe check the sensor to make sure it's plugged in all the way?

 

It's a downstream O2 performance code as viciouskind stated. It's only to monitor how well the converter is working. It wont affect how the truck is running so you shouldn't be too worried.