grblHAL Error 20
grblHALErrorPosition is kept
The line has a G or M code this controller doesn't know.
Position is kept. An error means the controller refused that one line or command, so nothing moved for it. (Hamrun's reading)
What to do
- Find the code on the line it stopped on (for example G41, M6 or G28.1 on some boards).
- Use the post-processor for your controller, or remove that command.
Official grblHAL message: “Unsupported or invalid g-code command found in block.” source
Got a different message?
Paste it into the decoder. Hamrun's editor checks your G-code before you run it, so a toolpath that leaves the machine's travel or a missing feed rate is caught before the machine stops.
Related codes
- GRBL 1.1 Error 20: The line has a G or M code this controller doesn't know.
- FluidNC Error 20: The line has a G or M code this controller doesn't know.
Official text copied from the grblHAL source on 2026-11-01. Steps and the position answer are Hamrun's reading unless marked “firmware says”. User reports are labelled CLAIMED.