GRBL Alarms & Errors

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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.


Alarm CodeMessageDescriptionExample
1Hard limitHard limit has been triggered. Machine position is likely lost due to sudden halt. Re-homing is highly recommended.Example
2Soft limitSoft limit alarm. G-code motion target exceeds machine travel. Machine position retained. Alarm may be safely unlocked.Example
3Abort during cycleReset 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.
4Probe failProbe 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. Your bit is likely making contact with the touch plate or the circuit is completed before the bit is moving. Move the bit away from the touch plate.Example
5Probe failProbe fail. Probe did not contact the workpiece within the programmed travel for G38.2 and G38.4. Your bit is too far away from the touch plate. Move the bit closer, it should be within 6-12mm (1/4 -1/2in) away.Example
6Homing failHoming fail. The active homing cycle was reset.
7Homing failHoming fail. Safety door was opened during homing cycle.
8Homing failHoming fail. Pull off travel failed to clear limit switch. The machine is within the limit switches range when it tries to move away. Try increasing pull-off setting or check wiring.Example
9Homing failHoming fail. Could not find limit switch within search distances. Try increasing max travel, decreasing pull-off distance, or check wiring. The limit switch wasn’t triggered in the distances expected. If your z-axis is moving away from the switch when homing, check your firmware and confirm you have the correct profile for your machine.Example


Error CodeMessageDescription
1Expected command letterG-code words consist of a letter and a value. Letter was not found.
2Bad number formatMissing the expected G-code word value or numeric value format is not valid.
3Invalid statementGrbl ‘$’ system command was not recognized or supported.
4Value < 0Negative value received for an expected positive value.
5Setting disabledHoming cycle failure. Homing is not enabled via settings.
6Value < 3 μsecMinimum step pulse time must be greater than 3μsec.
7EEPROM read fail. Using defaultsAn EEPROM read failed. Auto-restoring affected EEPROM to default values.
8Not idleGrbl ‘$’ command cannot be used unless Grbl is IDLE. Ensures smooth operation during a job.
9G-code lockG-code commands are locked out during alarm or jog state.
10Homing not enabledSoft limits cannot be enabled without homing also enabled.
11Line overflowMax characters per line exceeded. Received command line was not executed.
12Step rate > 30kHzGrbl ‘$’ setting value cause the step rate to exceed the maximum supported.
13Check DoorSafety door detected as opened and door state initiated.
14Line length exceededBuild info or startup line exceeded EEPROM line length limit. Line not stored.
15Travel exceededJog target exceeds machine travel. Jog command has been ignored.
16Invalid jog commandJog command has no ‘=’ or contains prohibited g-code.
17Setting disabledLaser mode requires PWM output.
20Unsupported commandUnsupported or invalid g-code command found in block.
21Modal group violationMore than one g-code command from same modal group found in block.
22Undefined feed rateFeed rate has not yet been set or is undefined.
23Invalid gcode ID:23G-code command in block requires an integer value.
24Invalid gcode ID:24More than one g-code command that requires axis words found in block.
25Invalid gcode ID:25Repeated g-code word found in block.
26Invalid gcode ID:26No axis words found in block for g-code command or current modal state which requires them.
27Invalid gcode ID:27Line number value is invalid.
28Invalid gcode ID:28G-code command is missing a required value word.
29Invalid gcode ID:29G59.x work coordinate systems are not supported.
30Invalid gcode ID:30G53 only allowed with G0 and G1 motion modes.
31Invalid gcode ID:31Axis words found in block when no command or current modal state uses them.
32Invalid gcode ID:32G2 and G3 arcs require at least one in-plane axis word.
33Invalid gcode ID:33Motion command target is invalid.
34Invalid gcode ID:34Arc radius value is invalid.
35Invalid gcode ID:35G2 and G3 arcs require at least one in-plane offset word.
36Invalid gcode ID:36Unused value words found in block.
37Invalid gcode ID:37G43.1 dynamic tool length offset is not assigned to configured tool length axis.
38Invalid gcode ID:38Tool number greater than max supported value.