After doing a UEM re-set, my car immediately displayed a check engine light and my car felt a rough idle. I un-powered the battery, and that re-set the light engine light only to come back on after driving a mile or so.

A code tester from Auto Zone displayed the code of #5 cyclinder mis-firing. I repalced the spark plugs as advised by Auto Zone, but still have symptoms of running on 4 cyclinders vs 5 and check engine light remains on.

What electricaly could I have interefered with to cause the failing of the #5 cylinder of my car immediately after I did UEM re-set test?

Your time/input is greatly appreciated.

Thanks

Not sure why it would have happened, but it sounds like a coil pack going my the sound and code.

First of all, I hope you've fixed your problem. My check engine light turned on for about a week and Volvo diagnosed it's misfired in cylinder #4. They performed a leakdown test and found lost of PSI in 4th and 5th cylinder. They quote me over $3000 to fix the problem. Please let me know how did you fixed your problem.

Ouch! Sorry to hear of the diagnosis. I got the random misfire code and was lucky that it was no worse than a new spark plug not working. If it's not the plugs or the coils, it may, unfortunately, be what the dealer told you. Do you have a trusted independent mechanic? That would probably save a good bit off the $3G estimate, but I'm afraid I can't contribute any substantive advice. Good luck and please keep us posted. You might also want to start your own thread here or in the general performance folder to get more attention to the specific issue.
Cheers,
Ed