Has anyone else found themselves with prints ‘failing’ at 99% due to the ‘unable to pull back filament’ error, but cancelling the print and selecting ‘Unload Filament’ in Bambu Studio works just fine?
It seems strange that one would work while the other throws an error…
P1S
AMS
PETG-BASIC (GRAY)
Yes I have had this happen. Annoyingly, if you are printing from makerworld it also means you can’t rate the print above 3 stars because it’s logged as a failed print.
Yes, i was getting this error in the early stages of the filament runout sensor switch sticking. I would tap the toolhead wnd it would complete the print as normal. Finally one day it would not clear so i remove the extruder.
I had to file the sides so the switch would move freely again. Still in service after 2200hrs.
One of the PTFE guides helps, as well as a “fix” for the AMS internals. Used to get them non-stop, after those two smooth sailing, cant remember the last time i had one.
I had failed to pull back errors when I got my first X1C/AMS and so I started using spool weights. Haven’t had a pull back error since on all my machine. Are spool weights the answer for everyone? I don’t know but it’s worked for me.
Sorry to reply after such a lapse.
It sounds like this would explain why all four spools of my AMS are subject to the problem. (Wouldn’t make sense for all four retractor motors to fail at once when slot 2 gets the majority of the work.)
Can you provide a resource for how to perform this fix? Or clarity on which part the ‘filament runout sensor switch’ is?
I’ve had the toolhead fully disassembled plenty of times, I just need to know the nomenclature.
Is it this part?
and this guide?
Which “fix” for the AMS internals are you referring to?
I will re-install my PTFE guide. It was difficult to remove, so I was leaving it off.
This is the sensor i was having trouble with. I repaired the old one and I’m stilll using it. But i also order a new one and tried it. Since it fixed my problem i decided to see if i could fix the old one and i did.
If I have to do it again i would just get a new one.
Here are the two fixes after which i never had a pull back error on P1 or X1:
Yes I had it happen. The problem was solved by installing a new filament cutter. The solution was suggested by someone on this forum. I don’t remember his name. I’m very grateful for the suggestion.
@dixonsally @Barryg41 @maximit @JonRaymond @RMB
Hi All.
Sorry if I’ve responded to some of you twice. The bot suggested I just name you all on a single reply, so that’s what I’m doing.
All of you have offered help, but thus far I’m still stuck.
As per @Barryg41 I replaced the sensor switch.
As per @maximit I have installed a PTFE guide on the toolhead inlet, the internal 4x PTFE guide, and the clip-on buffer output guide from @SPStudio. So far the issue continues. I’m going to continue to add these fixes. (Unfortunately my digital caliper died so I can’t accurately measure my 6-pin cable head for the next fix in line.)
@JonRaymond , I have not yet looked into spool weights. I will try that next.
@dixonsally, I have replaced the filament cutter as well to no avail.
I also confirmed that all my PTFE tubes are of Bambu Labs origin. (I have others sitting around, but I note that the BL versions have a larger inner diameter, so I’ll stick with those.)
I’ll update once the spool weights and the remainder of the fixes from @SPStudio have been tried.
In the meantime, are there other suggestions out there?
Have you tried a Support ticket? This forum is great, along with the Wiki, but if you’re going to start throwing parts and mods at an issue I would think the smartest move would be getting a proper diagnosis first. Sometimes the error codes aren’t exactly aligned with the real cause.
Just a comment on the spool weights. I use desiccant spool containers for two reasons. One is for the extra desiccant in the AMS and the other is to make sure the spool halves never come apart.
Never thought about the extra weight.
In fact, this is the ONLY mod i use on my printer setup.
Original PTFE tubes in both printer and both AMSs. Original extruder and hotend.
All original fans with no mods.
Never get an error.
2400hrs. She has been a very good printer. 
It just works.
I had this happen to me and it was driving me bat ■■■■ crazy. I installed a side spool holder that interfered a little bit with the tube going free m the block on the back of the Bambu X1C. That tube needs to be free where it can expand and contract and move. If you interfere with that tube in any way shape or form, filament will load then it will unload it will load it will unload, but you can manually feed it in and it’s fine. The minute I took that side spool holder off that wrapped around the back Where it interfered with that tubes, free moving, my problem went away. Take a look and watch that tube During a normal print that tube on the left-hand side, if you’re looking at the printer from the front, will expand out and expand in during the print that’s what it’s supposed to do. I interfered with that.
The PTFE coming out of the Buffer is critical in the filament feed as you found out, anything that restricts the slide movement can cause hiccups and throw errors like clogged nozzle etc. Problems often have people pointing at the extruder and AMS. It’s handy to know, and easy to check.
@Barryg41 @JonRaymond @michael.ray.neal @GenericUser @maximit @RMB
I have started a support ticket as per @GenericUser’s suggestion.
They doubled down on the need to ensure the buffer inlet and output PTFE tubes are happy. Then I asked the big question: “Why, if this is due to resistance along the PTFE tube path, does the printer successfully execute the ‘Unload Filament’ routine each and every time? Would the ‘Unload’ procedure not encounter the very same amount of resistance? Why then would this continue to succeed while the retraction procedure in the printing workflow continues to fail?”
They suggested it will be fixed in the next firmware release. I can’t tell if they’re just placating me or if my point is actually valid. Can you all confirm that the issues you experienced were the same? (Specifically that the prints fail at 99% but the ‘unload filament’ button works fine?)
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