AMS Ejects Adjacent Filament When a Roll Is Nearly Empty

Bambu Lab AMS Troubleshooting
1

Issue

I’m experiencing a strange issue where the AMS is ejecting filament unexpectedly. All filaments used are Bambu brand, either PLA or PETG.

Steps to Reproduce

  1. All AMS settings are enabled (insertion update, update on startup, update remaining capacity, and AMS filament backup).
  2. Four rolls of filament are loaded in the AMS: three are full/near full, and one has ~20 g remaining. Order:
  • Slot 1: full
  • Slot 2: full
  • Slot 3: ~20 g
  • Slot 4: full
  1. Power cycle the printer (turn off, then on).
  2. All filaments are detected correctly, but the roll immediately to the left of the ~20 g roll gets fully ejected.

Troubleshooting Done

  • Disassembled the AMS and confirmed all Bowden tubes are clear.
  • Re-tested with different slot orders:
    • Slot 4 loaded first (full), then slot 3 (full), then slot 2 (full), then slot 1 (~20 g).
    • In this configuration, the roll in slot 2 was ejected instead.

It seems the presence of a nearly empty (~20 g) roll is causing the adjacent slot to eject, which seems unusual.

Suspected Cause

My suspicion is that the “Update Remaining Capacity” setting, when paired with the ~20 g roll, may be triggering this behavior. I will test with that setting disabled to see if the issue persists. However, this appears to be a bug.

System Information

  • Printer: Bambu Lab P1S
  • AMS: 1 unit
  • Filament:
    • Bambu Basic PLA (white, blue)
    • Bambu PETG (black)
    • Bambu PLA Galaxy Green (~20 g remaining)

Notes

  • The issue occurs during filament detection (e.g., on startup), not during active printing.
2

You might want to update your report with the firmware version (please don’t say “the latest version”, that isn’t a choice on a bug report form). It’s easier to collect the firmware and AMS version numbers from Bambu Studio instead of the device screen.

Also to clarify for their report, by eject do you mean it totally unloads the filament so it is no longer in the AMS feeder nozzle at all and the filament end is dangling loose around the spool? If so that sounds like a serious bug.

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