Q: window motor doesn't always work on 2001 Buick Century

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
Sometimes the front left window will not go up or down
(3) Answers
Most likely a faulty window motor. The only way to know for sure is to remove the door panel and test the motor while it is not working.