The check engine light came on and I checked the codes...403...and related codes with my Diablo. This doesn't sound particularly serious. Is this a part that I can purchase and replace or does it need to go back to the dealer for repair?

Does it trip with the diablo on and with it set to stock?

Also I have thrown that code but the CEL has stayed off. I would try driving it a bit and checking for DTC codes even if you havent seen the light.

Also what exxhaust do you have and do you have a EGR blocker and a finger stick?

No, I don't have a finger stick or EGR blocker. I installed a cat-back 4" MBRP exhaust.

I don't yet know if the light will stay on when the truck is back on stock. I only have it boosted 85 hp. I've never having it boosted more than that. I assumed some circuit sensor just got sooted up from the extra exhaust the chip throws.