Bambu Lab HMS error code 0300-0300-0001-0001 signals a fault in the part cooling fan circuit. The 0300-0300 subgroup covers toolhead fan systems, and this error indicates the printer detected a problem with the part cooling fan — either it failed to start, stopped unexpectedly, or its speed feedback is outside the expected range.

What the Error Means

The part cooling fan is monitored by the printer firmware via a tachometer signal. Suffix 0001-0001 in this subgroup typically indicates the fan speed is not being detected at all — meaning the fan is not spinning or is spinning too slowly to generate a tach signal. This can be caused by a fan obstruction, a failed bearing in the fan motor, a disconnected cable, or a blown motor driver on the toolhead PCB.

Step-by-Step Fix

1. Power off the printer and let the hotend cool before accessing the toolhead.
2. Visually inspect the part cooling fan blades for filament debris, dust buildup, or a string of plastic that has wrapped around the shaft and locked the rotor.
3. Clear any obstruction from the fan blades and shaft with a pair of tweezers. Be careful not to damage the blades.
4. Manually spin the fan blades with a fingertip — they should rotate freely with very little resistance. Stiff or grinding rotation indicates a bearing failure.
5. Check the fan cable at the toolhead PCB connector. Reseat the connector and confirm no pins are bent or pushed back.
6. Power the printer on and navigate to the diagnostics screen to run the fan test. Confirm the part cooling fan spins at full speed.
7. If the fan does not spin or produces a grinding noise, replace it with a compatible model-specific spare.

Parts Required

• Part cooling fan (toolhead-specific for your Bambu Lab model — check the official spare parts listing)
• Tweezers for debris removal
• Small Phillips or hex screwdriver for fan access

If the fan tests healthy but the error recurs during printing, the toolhead PCB fan driver may be intermittently faulty — contact Bambu Lab support for a toolhead PCB evaluation.