Bambu Lab HMS error code 0300-0200-0001-0003 indicates that the nozzle thermistor circuit has shorted. Unlike error 0001-0001 (open circuit), a short circuit means the thermistor is reporting an implausibly high temperature — often reading at or near its maximum range — because two conductors in the circuit have made unintended contact.

What the Error Means

Within the 0300-0200 hotend thermal subgroup, suffix 0001-0003 points to a short circuit condition in the thermistor. This can be caused by a damaged thermistor where internal insulation has broken down, wiring that has been pinched or burned causing the insulation to fail, or a connector with bridged pins. Because the printer cannot trust nozzle temperature readings in this state, it refuses to operate the hotend heater.

Step-by-Step Fix

1. Power off the printer and allow the hotend to cool to room temperature. Do not attempt inspection while the hotend is hot.
2. Remove the toolhead cover for your printer model and visually trace the thermistor cable from the heater block to the toolhead PCB connector.
3. Look for areas where the cable may have been pinched by the toolhead assembly, rubbed against a metal edge, or burned by contact with the heater block surface.
4. Unplug the thermistor connector from the toolhead PCB. Use a multimeter in resistance mode and measure across the two thermistor pins. At room temperature a healthy thermistor reads 80–120 kΩ. A reading close to zero (short circuit) confirms the fault.
5. Inspect the connector itself for bridged or bent pins. If the pins look fine, the thermistor body or wiring insulation has failed and replacement is needed.
6. Install a new thermistor, ensuring the tip is fully seated in the heater block pocket and all wiring is routed away from sharp edges or hot surfaces.
7. Power on and verify the temperature reading is stable and within expected range at room temperature before running a preheat.

Parts Required

• Hotend thermistor (NTC 100K, compatible with your Bambu Lab toolhead)
• Multimeter for resistance measurement
• Small flat-head or cross-tip screwdriver for connector inspection
• Cable management clips or Kapton tape to reroute the replacement wire safely

If the replacement thermistor produces the same short-circuit error, the fault may lie in the toolhead PCB or wiring harness — reach out to Bambu Lab support for further diagnosis.