Grbl enters an alarm state when it detects a serious issue that could compromise safety or accuracy. Alarms stop all operations and require user intervention before continuing.
Alarms help prevent damage to your machine or workpiece. After resolving the issue, you must unlock Grbl with the $X command before resuming normal operation.
Alarm Code Reference
| Alarm Code | Name | Description |
1 |
Hard limit triggered | A hard limit switch was activated, indicating the machine hit a physical limit. This triggers an immediate stop. Homing is recommended afterward to re-establish position. |
2 |
Soft limit alarm | The machine attempted to move beyond its configured soft limits. The position is retained and can be safely unlocked. Check your travel limits and commands. |
3 |
Reset while in motion | Grbl was reset while executing motion. The position is likely lost and homing is recommended to re-establish accurate coordinates. |
4 |
Probe fail (triggered early) | The probe was already triggered before the probing move began. Check probe wiring or mechanical setup. |
5 |
Probe fail (not triggered) | The probe did not trigger within the set distance during a probing move. This may indicate a connection issue or a missed surface. |
6 |
Homing fail (not enabled) | Homing cycle was requested but the homing feature is not enabled in settings ($22). Enable it to use homing. |
7 |
Homing fail (no switch hit) | The machine could not detect a limit switch within the homing seek distance. Check switch wiring or mechanical operation. |
8 |
Homing fail (pull-off not cleared) | The pull-off motion did not clear the limit switch after triggering. This may suggest mechanical binding or switch problems. |
9 |
Homing fail (safety door opened) | The safety door was opened during a homing cycle. The operation is aborted to ensure safety. Close the door and retry. |
10 |
Homing fail (travel exceeded) | The pull-off move exceeded machine travel limits. The homing switch may be in an unreachable location. Adjust your homing settings or reposition switches. |
Clearing an Alarm
-
Identify the alarm code. Grbl will return an
ALARM:Xmessage. -
Fix the root cause. This might involve checking connections, switches, or software commands.
-
Unlock Grbl. Send
$Xto unlock the controller after resolving the problem. -
Re-home the machine (if required) to re-establish an accurate position.