HMS 0300-0800-0001-0003: abnormal Motor-Z resistance
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HMS 0300-0800-0001-0003 means the Z motor is measuring outside the resistance the firmware expects. That is a different message from the open-circuit code: the circuit is complete, but the winding is not what it should be. A loose connector cannot produce this, so the motor is usually the answer.
Affected machines: A2L and P2S. The Z motors carry the bed and everything on it, run hot on long prints, and stall against a crash rather than slipping. Between them, those three facts explain most winding failures on this axis.
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What the reading should look like
A healthy stepper has two coils with almost identical resistance, typically a few ohms each. The useful test is not the absolute number but the comparison: the two pairs on one motor should match each other, and the motors on a machine should match each other too.
Measure cold. Winding resistance rises with temperature, and a motor measured immediately after a long print can read high enough to look faulty when it is not. If a reading looks marginal, let the machine sit for half an hour and repeat it.
Printer stops with abnormal Motor-Z resistance, sometimes after a crash or a long print
Partially failed stepper winding, occasionally a marginal connector
- Power off at the wall and let the printer cool to room temperature before measuring.
- Unplug each Z motor and measure resistance across both coil pairs.
- Compare the two pairs on the same motor. A difference of more than a fraction of an ohm points at the winding.
- Compare that motor with the other Z motor on the machine. The odd one out is the one to replace.
- Check each pin against the motor body. Any continuity there means a winding has shorted to the can.
- Fit the correct replacement for your model, set the coupler at the original height, and re-level the bed.
If both motors measure the same and the code persists, the fault is the board’s measuring circuit rather than the motor. That is a service item, not a part swap, and replacing motors will not clear it.
The companion fault is Motor-Z open circuit, which points at the loom instead. Our page on the lead screw explains the load this motor carries, and the troubleshooting index covers the rest.
HMS 0300-0800-0001-0003 FAQ
What resistance is normal for a Z stepper?
A few ohms per coil, and the two coils should match. The match matters more than the number.
Why does a warm motor read differently?
Copper resistance rises with temperature. Measure cold or you will condemn a healthy motor.
Can a crash cause this?
Yes. A hard stall drives current into a stationary winding, and that is how many of these failures start.
Should I replace both Z motors at once?
Not necessary. They are independent, and a matched pair is not required on these machines.
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