Weird G29 behavior

[tsteever]

When performing the procedure my arm drops, then the Z descends and then moves back up before moving down again to probe the bed. The weird part is that I thought that is was supposed to move down and when the probe touches go back up and then descent again at a lower rate for accuracy. On my printer the probe never touches the bed before it moves back up. The slower decent does probe the bed.

Is this normal?

[Roxy]

What happens if you manually trigger the switch before it moves very far? Does it recognize the switch got pressed?

[tugeagon]

I had a similar issue, it ended up being the wiring to the switch was getting pulled while extending the arm. Marlin thought it was triggered so it never touched the glass.