HMS 0300-E000-0001-0004: Hotend Rack Motor Is Stalled
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HMS 0300-E000-0001-0004 means the hotend rack motor is stalled, and asks you to check for foreign objects blocking movement or possible collisions with the toolhead. The motor is powered and trying; something physical is stopping it.
Almost always it is a blob of purged filament that has welded itself somewhere it should not be. The rest of the time it is a cable routed into the path.
Where to buy
Look where you cannot see
A USB borescope gets behind the toolhead without dismantling it. On this fault that is the whole job: once you can see the obstruction, removing it is trivial.
Light it properly first
A rechargeable headlamp keeps both hands free and puts the light where you are looking instead of where the bench lamp points. Half of what gets called an invisible fault is an unlit one.
Get the debris out without levering on anything
A long precision hook and pick set reaches cold purge fragments wedged beside the rack. Levering with a screwdriver against a plastic housing turns a blockage into a broken bracket.
Then move it by hand before powering up
With the machine off, move the rack through its travel by hand. It should be smooth end to end. A tight spot you can feel is the thing the motor was fighting.
How HMS 0300-E000-0001-0004 differs from an open circuit
A motor the machine cannot reach is HMS 0300-E000-0001-0001. A stall means the electrical path is fine and the mechanical one is not.
What keeps causing it
Purge debris accumulating near the rack, which the rack guide code HMS 0500-0300-0001-000D also touches on. Method is in troubleshooting and the nozzle side in nozzle cleaning.
HMS 0300-E000-0001-0004 FAQ
Can I force it by hand?
Move it gently with the power off. Never force it.
What is usually in the way?
Cold purged filament. It welds itself into corners.
Will a restart clear it?
Only if the obstruction has moved. Usually it has not.
Could the motor be failing?
Possible, but a stall points at the mechanism first.
Debris stops more than one mechanism in the toolhead. HMS 07FE-8000-0001-0001 means extruder switching is abnormal, and it names the flow blocker and filament jammed inside the head as the two places to look.
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