Hey I found it. I knew I had it someplace.
Anyway, in case someone else wants to check their Pfaff 2170, the steps are:
1. Go to Main Menu
2. Press red button at bottom of screen
3. go to Machine test
4. Type in code 4021
5. press OK at bottom of screen
6. Go to Operating Times
It's listed by Days:Hours:Minutes:Seconds
I don't know if it'll work on other Pfaffs.