Throwing a Code--Part Nonexistent

[eighthundreddollaranger]

I had to replace the main computer on my 92 and it's been throwing codes for a fault in an optional exhaust control component that my truck doesn't have. It is possible that the computer came from a truck that DID have it, but I was also wondering if there is another reason it might throw that code? I don't have the exact name of the part or the code number on hand so I understand if that's needed for a constructive response, but I figured I'd throw this info out there just in case someone knows offhand. Will update with more information when I can.