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Bambu Lab · FDM 3D Printers
AMS Filament Backup - Filament Buffer Tube Has Excessive Slack
Quick Answer
Error code 0500_0400 on your Bambu Lab FDM 3D Printers means: AMS Filament Backup - Filament Buffer Tube Has Excessive Slack. This is usually fixable — see the step-by-step guide below.
Likely Causes
  1. PTFE tube between AMS and tool head has a loop or kink creating excess filament in the path
  2. Retraction settings causing filament to bunch up in the buffer tube
  3. AMS hub feeding filament faster than the extruder is consuming it
  4. PTFE tube is too long for the printer configuration
How to Fix It
1
Check the PTFE tube routing from the AMS to the tool head for loops or kinks
2
Unload the filament completely and verify the PTFE tube is the correct length for your setup
3
Verify the filament path is clear by blowing air through the tube
4
Reseat the PTFE tube connectors at both the AMS hub and the tool head
5
If using a third-party PTFE tube, ensure it matches the Bambu Lab specification (2mm ID / 4mm OD)
Pro Tip
This fix requires some technical knowledge. If you're unsure about any step, consider contacting support or a qualified technician.
Parts You May Need
Replacement PTFE tube (Bambu Lab OEM recommended)
PTFE tube couplers
Related Error Codes
0300_01000300_02000300_03000300_04000500_0100
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