HMS 0700-0100-0001-0003: AMS Assist Motor Torque Control Malfunctioning
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HMS 0700-0100-0001-0003 means the AMS cannot control the assist motor by torque any more, and Bambu suspects the current sensor. Torque is measured as motor current, so genuine resistance in the filament path produces the same high reading as a broken sensor. Rule out the drag before you accept the diagnosis.
The assist motor is the one that pulls filament off the spool and keeps slack in the path. It works against whatever friction you have given it.
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Why current and torque are the same number
A motor pushing against resistance draws more current, so the AMS infers load from current. That inference is only as good as the sensor, which is why Bambu names it. It is also only as good as the assumption that nothing else changed — and the thing that usually changed is the path.
The test that costs nothing
Bypass the AMS and feed the same spool from the external spool holder. If printing is normal, the filament and the spool are fine and the fault is inside the unit. If it is still laboured, you have found real drag and the sensor was telling the truth. This single test decides whether to open anything at all.
Where the drag actually comes from
A spool that does not turn freely on its seat, a PTFE path with a tight bend behind the printer, and filament rubbing against the inside of its own coil all raise the current the motor needs. Tube condition and routing are covered in PTFE tube for 3D printers, and the hub that the path runs through is in the AMS hub.
What HMS 0700-0100-0001-0003 shares with the slip code
A motor that cannot regulate torque eventually loses grip, which is reported separately as HMS 0700-0100-0001-0001. If you are seeing both, treat them as one fault with two symptoms rather than two repairs.
The other half of the control loop
Torque control and speed control are separate loops with separate sensors, and the speed version is HMS 0700-0100-0001-0004. Which one appears tells you which half of the loop stopped reporting, and that is genuinely useful before ordering anything.
HMS 0700-0100-0001-0003 FAQ
Can I print while it shows?
Often yes, in single-material mode from the spool holder. Multi-material switching is what actually depends on this motor behaving.
Is the current sensor replaceable on its own?
No. It sits on the AMS board, so the practical repair is a board or unit swap through Bambu rather than a component.
Does cold weather cause it?
It can contribute. Filament is stiffer when cold and a stiff coil drags more, which raises the current the motor needs.
Would lubricating the path help?
A little, on the filament itself rather than on the gears. Keep grease away from the extrusion wheels, which rely on grip — see printers with an AMS for how the path is laid out.
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