The GRBL firmware has a whole list of Alarms and Error codes that you can encounter when running your CNC. gSender will always display a question mark when there’s an alarm which you can hover over for more information about why it happened and errors will appear as a hovering box in the bottom corner of the visualizer.
Alarms
| Alarm Code | Message | Description | Example |
| 1 | Hard limit | Hard limit has been triggered. Machine position is likely lost due to sudden halt. Re-homing is highly recommended. | Example |
| 2 | Soft limit | Soft limit alarm. G-code motion target exceeds machine travel. Machine position retained. Alarm may be safely unlocked. | Example |
| 3 | Abort during cycle | Reset while in motion. Machine position is likely lost due to sudden halt. Re-homing is highly recommended. May be due to issuing g-code commands that exceed the limit of the machine. | |
| 4 | Probe fail | Probe fail. Probe is not in the expected initial state before starting probe cycle when G38.2 and G38.3 is not triggered and G38.4 and G38.5 is triggered. | Example |
| 5 | Probe fail | Probe fail. Probe did not contact the workpiece within the programmed travel for G38.2 and G38.4. | Example |
| 6 | Homing fail | Homing fail. The active homing cycle was reset. | |
| 7 | Homing fail | Homing fail. Safety door was opened during homing cycle. | |
| 8 | Homing fail | Homing fail. Pull off travel failed to clear limit switch. Try increasing pull-off setting or check wiring. | |
| 9 | Homing fail | Homing fail. Could not find limit switch within search distances. Try increasing max travel, decreasing pull-off distance, or check wiring. |
Errors
| Error Code | Message | Description |
| 1 | Expected command letter | G-code words consist of a letter and a value. Letter was not found. |
| 2 | Bad number format | Missing the expected G-code word value or numeric value format is not valid. |
| 3 | Invalid statement | Grbl ‘$’ system command was not recognized or supported. |
| 4 | Value < 0 | Negative value received for an expected positive value. |
| 5 | Setting disabled | Homing cycle failure. Homing is not enabled via settings. |
| 6 | Value < 3 μsec | Minimum step pulse time must be greater than 3μsec. |
| 7 | EEPROM read fail. Using defaults | An EEPROM read failed. Auto-restoring affected EEPROM to default values. |
| 8 | Not idle | Grbl ‘$’ command cannot be used unless Grbl is IDLE. Ensures smooth operation during a job. |
| 9 | G-code lock | G-code commands are locked out during alarm or jog state. |
| 10 | Homing not enabled | Soft limits cannot be enabled without homing also enabled. |
| 11 | Line overflow | Max characters per line exceeded. Received command line was not executed. |
| 12 | Step rate > 30kHz | Grbl ‘$’ setting value cause the step rate to exceed the maximum supported. |
| 13 | Check Door | Safety door detected as opened and door state initiated. |
| 14 | Line length exceeded | Build info or startup line exceeded EEPROM line length limit. Line not stored. |
| 15 | Travel exceeded | Jog target exceeds machine travel. Jog command has been ignored. |
| 16 | Invalid jog command | Jog command has no ‘=’ or contains prohibited g-code. |
| 17 | Setting disabled | Laser mode requires PWM output. |
| 20 | Unsupported command | Unsupported or invalid g-code command found in block. |
| 21 | Modal group violation | More than one g-code command from same modal group found in block. |
| 22 | Undefined feed rate | Feed rate has not yet been set or is undefined. |
| 23 | Invalid gcode ID:23 | G-code command in block requires an integer value. |
| 24 | Invalid gcode ID:24 | More than one g-code command that requires axis words found in block. |
| 25 | Invalid gcode ID:25 | Repeated g-code word found in block. |
| 26 | Invalid gcode ID:26 | No axis words found in block for g-code command or current modal state which requires them. |
| 27 | Invalid gcode ID:27 | Line number value is invalid. |
| 28 | Invalid gcode ID:28 | G-code command is missing a required value word. |
| 29 | Invalid gcode ID:29 | G59.x work coordinate systems are not supported. |
| 30 | Invalid gcode ID:30 | G53 only allowed with G0 and G1 motion modes. |
| 31 | Invalid gcode ID:31 | Axis words found in block when no command or current modal state uses them. |
| 32 | Invalid gcode ID:32 | G2 and G3 arcs require at least one in-plane axis word. |
| 33 | Invalid gcode ID:33 | Motion command target is invalid. |
| 34 | Invalid gcode ID:34 | Arc radius value is invalid. |
| 35 | Invalid gcode ID:35 | G2 and G3 arcs require at least one in-plane offset word. |
| 36 | Invalid gcode ID:36 | Unused value words found in block. |
| 37 | Invalid gcode ID:37 | G43.1 dynamic tool length offset is not assigned to configured tool length axis. |
| 38 | Invalid gcode ID:38 | Tool number greater than max supported value. |