(BUG) 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.
  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.

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Update:

  1. I’m uploading a video so you can see what happens. This time I loaded the 20g filament in slot 2 and it ejected the filament in slot 1. Definitely not an issue with the slots themselves. Sorry in advance for the shake camera and long video! Skip to 2:00 to see the issue immediately. https://m.youtube.com/watch?v=bEggR6ImQx0&pp=0gcJCRsBo7VqN5tD

  2. Turning off the AMS setting to update remaining capacity fixes it.

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.

1 Like
3

Thanks just updated. Yes, it completely unloads the filament, I.e. no longer loaded in the ams feeder nozzle at all.

1 Like
4

Please tag this “bug report” (pencil icon on the thread title and select optional tag).

5

@mugglesmuggle I was trying to do that but I don’t see the ability to add an optional tag when I edit.

6

Working with Bambu support on this issue, they believe it has to do with the tight spool. Even with AMS setting to update remaining capacity off, this happend to me again so I loosend the spool and then it seemed to be fine. The weird thing is that it ejects a complelty different spool when this occurs, which they are still looking into. In the meaintine, if this happens to anyone - loosen the spool a bit and it should be fine.