Bambu Lab HMS error code 0700-4500-0002-0003 is an AMS buffer sensor fault within the 0700-4500 buffer subgroup. While 0002-0001 indicates a general buffer error, suffix 0002-0003 specifically points to a fault in the sensor that monitors the buffer state — the sensor is either not responding, reporting an implausible value, or is physically damaged.

What the Error Means

The buffer sensor monitors the tension and fill level of the filament accumulator. Without this sensor, the AMS cannot determine when to feed more filament into the buffer, leading to over-feeding (buffer full jam) or under-feeding (buffer empties, extrusion starves). Suffix 0002-0003 means the sensor circuit itself has a fault — independent of whether the buffer has filament in it or not. Causes include a disconnected sensor cable inside the buffer unit, a broken sensor lever, debris jamming the sensor mechanism, or a sensor that has failed electrically.

Step-by-Step Fix

1. Power off the printer and AMS before opening the buffer unit.
2. Locate the buffer sensor — typically a microswitch with a lever arm that is deflected by filament tension inside the buffer.
3. Inspect the sensor lever for physical damage (bent, broken, or seized). A lever that is stuck fully depressed or fully released will report a constant state regardless of actual buffer fill.
4. Clear any debris from around the sensor lever and confirm it moves freely through its range.
5. Check the sensor wiring connector inside the buffer unit. Reseat the connector firmly.
6. Close the buffer and power on. Initiate a load cycle and observe whether the buffer sensor now transitions correctly between empty and filled states.
7. If the sensor is mechanically intact and the wiring is secure but the error persists, replace the sensor assembly.

Parts Required

• AMS buffer sensor (microswitch assembly, model-specific)
• Tweezers for debris clearing

Contact Bambu Lab support to obtain the correct buffer sensor part for your AMS version and for guidance on its replacement.