SO3 CM4 GRBL 4.1 Homing Errors Suddenly

My EARLY SO3 running GRBL 4.1 and CM4 stopped homing properly today with ZERO changes.

The Z axis moves up a few MM, stops briefly, then moves up a few more MM rapidly, then stops. I get multiple errors in CM:

  1. Limit Switch Error Z
  2. GRBL ERROR: Homing Failed, pull off didn’t clear
  3. Homing Cycle Failed

If it gets to the Z axis limit switch it bounces off of it repeatedly.

I have checked everything I can think of with no success.

Anyone have any ideas?!

Gotta ask…are you sure the switch hasn’t failed? Looks like the switch has failed “closed” - check and be sure it actually works?


As @mikep noted it sounds as if the switch has failed — see if your board has lights for the switches — if so, the appropriate light should light when the switch is closed.

Contact us at and we’ll do our best to help you sort this out.

1 Like

You were dead-on; z-axis limit switch is dead.
My frustration clouded my troubleshooting.

You were dead-on. The z-axis limit switch is not responding.
My frustration clouded my troubleshooting.

1 Like