HI Ed. The diagnostic system would not fail. As a component of cars, it's a fairly large item (not necessarily physically large though). The whole system might fail say for instance in a case of a flood, but day in/day out, no. Parts of the system can and do fail on cars all the time. It sounds like...

Hm, not much meat on those bones... I'd take it back in and get to the next step. Then when it turns out to be something else, ask for a refund or partial refund for the MAP sensor replacement.