HMS 0300-0800-0001-0001: Motor-Z open circuit
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HMS 0300-0800-0001-0001 means a Z motor reads as an open circuit. The bed will not rise or fall, so the printer cannot home Z and will not start a print. As with the other open-circuit codes, a broken connection is more likely than a dead motor, and the connectors at the base of the machine are where to look first.
Affected machines: A2L and P2S. These machines drive the bed on lead screws with their own motors, and the loom to them runs down the frame past everything that vibrates. The Z motors are also the ones people disturb when clearing a crash or removing the bed.
Where to buy
Finding which motor, and which wire
The code names the circuit, not the corner. The fastest way to narrow it down is to compare: unplug each Z motor at its connector and measure across the coil pairs. The bad one stands out immediately, because a healthy stepper reads a few ohms and a broken circuit reads nothing at all.
If every motor measures healthy, the break is between the plug and the board. That is usually a pin that has backed out of its housing, and it is worth pushing gently on each wire at the back of the connector before ordering anything.
Bed does not move, Z homing fails, or the printer stops with Motor-Z open circuit
Broken connection in the Z motor circuit, occasionally a failed winding
- Power off at the wall and let the bed rest on its stops before working underneath it.
- Unplug each Z motor at its connector and inspect the pins in both halves.
- Measure resistance across each coil pair at the motor. A few ohms is healthy; an open reading identifies the faulty one.
- If the motor reads healthy, reseat the plug and measure again at the board end to isolate the cable.
- Fit the correct replacement for your model, keeping the coupler position on the lead screw as it was.
- Re-level the bed after the repair, because any work on a Z motor moves the reference.
Do not skip the re-level. A coupler that goes back a fraction of a turn out of place changes where the nozzle meets the plate, and the first layer will tell you about it in a way the error log will not.
The related fault is abnormal Motor-Z resistance, which points at the motor rather than the wiring. Our page on the lead screw covers the mechanism this motor drives, and the troubleshooting index covers the rest.
HMS 0300-0800-0001-0001 FAQ
Can I print with one Z motor working?
No. The bed would tilt as it moved, and the firmware stops before that happens.
Which Z motor does my machine take?
They differ between the A2L and the P2S. Match the part to the model rather than to the look of the motor.
Do I need to re-level afterwards?
Yes, every time. Any work on a Z motor or coupler changes the reference the mesh was built against.
Could the lead screw be the problem?
Not for this code. A stiff screw gives a stall or a stuck-motor error, not an open circuit.
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