2004 GMC Envoy P0410 code, secondary air injection system m

Hello. I was wondering if you could help me out with the P0410 code that came up on my Enjoy. I just spent a painful Sunday replacing the thermostat, drove it for two days, ran the AC and heat and now I have this code. I fired up the truck this morning and the RPMs were going up and down when I engaged the heater. Any help would be great. Thanks!