grbl/doc/csv/alarm_codes.csv

1	1	Hard limit	Hard limit has been triggered. Machine position is likely lost due to sudden stop. Re-homing is highly recommended.
2	2	Soft limit	G-code motion target exceeds machine travel. Machine position safely retained. Alarm may be unlocked.
3	3	Abort during cycle	Reset while in motion. Grbl cannot guarantee position. Lost steps are likely. Re-homing is highly recommended.
4	4	Probe fail	If 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.
5	5	Probe fail	If the probe fails to contact the workpiece within the programmed travel for G38.2 and G38.4.
6	6	Homing fail	If the active homing cycle was reset.
7	7	Homing fail	If the safety door was opened during homing cycle.
8	8	Homing fail	Pull off travel failed to clear limit switch. Try increasing pull-off setting or check wiring.
9	9	Homing fail	Failed to find limit switch within travel. Defined as `1.5 * max_travel` on search and `5 * pulloff` on locate phases.