"Reduced Engine Performance", '08 S80 (after emission test)
 

Starting the car after the emission test, the engine was not working well and provided the message "reduced engine performance". I tried restarting numerous times, but it did not self-correct.

I then disconnected the battery cables and touched them together for a minute to reset the computer. The car started and ran well and continues to do so since (3-4 outings).

However, I'm concerned what caused the original message. I've searched threads, but not found a solution. Any ideas? Is this likely to happen again? Could the emission test plugging in to the car have caused the problem?

Thank you in advance for all comments and help!