Why is my phone no longer vibrating?

I recently replaced the battery, screen/glass, and charging assembly on my Pixel 2. Everything seems to be fine, except for a single issue— my phone is no longer vibrating for haptic feedback, message notification, or phone calls.

Because there were no new units available, I ordered a used charging assembly for my repair. I imagine the most likely reason for the issue I’m experiencing is that a) I have a bad vibration motor on the new-to-me charging assembly, or b) I messed something up during installation, which is causing my vibration motor to malfunction.

But that said, I’m not actually sure what’s wrong, how to diagnose it, or what to do in order to fix it. Any thoughts or guidance on how to deal with this issue?