check engine light and tune

[E_Low]

I have a SCT 4 bank chip, and if i run the dyno tune i had done i get the check engine light after about 80 miles. If i run the stock tune the check engine light doesnt come on. what would cause this?

[E_Low]

Its on a 03 gt. mods are: longtubes, o/r x with mil eliminators, upper plenum, 75mm tb, cai, and the 4 bank chip.

[SSMAN]

What code doe it throw?

[E_Low]

its been awhile since i pulled the actual code again, but i believe it is 1131 (which is o2's)