Possibly broke the Z limit switch

[LarryM]

Use this:

[Guide] Using Grbl to debug your homing switches

If you are having difficulties with your homing switches you can do a quick test with Grbl to see what the state of the homing switches is from Grbl’s point of view. NOTE: In order to use this procedure you need to have grbl Version 0.9j or later installed on your Arduino. To do so, you use the Grbl status immediate command ? (question mark). This command asks Grbl for its current value of some of its state information. For the purpose of this article we are interested in the homing switch stat…