Generator was faulted for Undervoltage 1902. Faulted January 25th at 14:00/exercise. Generator also had the Code 0 alarm due to the service/maintenance history needing to be reset. I performed a maintenance reset and was able to clear the Code 0 Alarm. Once cleared, I started and ran generator while monitoring voltage and frequency output to be normal, 240v/60hz. I updated firmware from 1.48 to 1.51. Visually inspected brushes. No apparent issues. Simulated an outage. Generator operated properly. #2 Service. No further issues.