HMS 0300-1800-0001-000C: eddy current sensor signal jump
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HMS 0300-1800-0001-000C means the eddy current sensor in the toolhead is producing a signal that jumps rather than moving smoothly. That sensor is how the printer knows where the nozzle is, magnetically, without touching anything. A jumping signal is the signature of a poor contact somewhere in that circuit, and only occasionally of a defective sensor.
Affected machines: A2L, H2S and P2S. The sensor sits alongside the nozzle and reads the metal of it, which means anything conductive that collects near the tip is in the measurement. Purge debris, a smear of melted filament and swarf from a scraped plate all count.
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Why contact beats sensor as an explanation
An eddy current sensor has no moving parts. It energises a coil and reads how the field changes when metal is near, so there is very little in it to fail outright. What does fail is everything around it: the connector at the toolhead board, the short loom to it, and the cleanliness of the area it is reading.
A jumping signal means the reading changes when it should not. Two causes produce that. A connector making intermittent contact, so the reading breaks and resumes. Or debris moving in the sensing field, so the reading genuinely changes because the magnetic picture changed.
Bed levelling fails, nozzle detection is erratic, or the printer reports a sensor signal jump
Intermittent connector at the toolhead, or conductive debris in the sensing area
- Power off and let the hotend cool completely.
- Clean around the nozzle and the sensor face with tweezers and isopropyl alcohol. Do not scrape metal against the sensor.
- Check that the nozzle is fully seated and tightened. A nozzle sitting proud changes what the sensor reads.
- Unseat and reseat the toolhead connector, looking for a pin that is not level with its neighbours.
- Run a bed levelling cycle and watch whether the failure repeats at the same point on the plate, which would point at the plate rather than the sensor.
- If the code persists with a clean, well-seated nozzle and a reseated connector, the sensor or its board is the remaining cause and that is a service item.
One easy mistake worth avoiding: a steel nozzle and a brass nozzle do not read the same to an eddy current sensor. If this started right after a nozzle change, run the machine’s own calibration before assuming anything has broken.
The non-responsive version of this fault is the eddy current sensor not responding. Our page on the hotend covers the assembly the sensor reads, and the troubleshooting index covers the rest.
HMS 0300-1800-0001-000C FAQ
Did my nozzle change cause this?
It can. A different nozzle material or a nozzle not fully seated changes what the sensor sees. Recalibrate first.
Can I clean the sensor face?
Gently, with isopropyl alcohol on a soft cloth. Never scrape it, and never use a metal tool on it.
Is this the same as the bed levelling sensor?
On these machines it is part of the same job. The eddy sensor is what makes touchless levelling possible.
Will printing continue with this code?
Levelling will be unreliable, so the first layer becomes a lottery. Fix it before starting anything long.
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