I encountered a “failure to retract filament” error on my X1C and am going through the maintenance for making sure everything is cleared. I have verified that everything from the AMS to the print head is clear of broken filament pieces. In working at the print head, now, I am having trouble removing the print head’s filament sensor for inspection and possible cleaning.
I ran into two issues.
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I cannot seem to get the sensor removed from the extruder assembly. I removed the two front 1.5 mm screws but the sensor unit refuses to slide out to the side as shown in the WIKI photos and multiple YouTube videos I have seen. It appears to be either a very tight fit or there is some other trick that I have not picked up on.
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The cable from the filament sensor to the print head appear to be “potted” at the print head side. The connector appears to be encased in an elastometric coating of some sort that prevents me from easily disconnecting the cable. The maintenance guides refer to using a heat source on the sensor cable but the photos are not clear or close up enough to see that it is what I am seeing. (The other cables were easy to disconnect.) Again, I have not noticed this in photos and videos. Is this something new? (The printer was purchased from BL in late January.)
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I also found that the left side of the print head cover was warped. It is not a functional issue but it took me some time to find out exactly where the whole extruder assembly was hanging up as I removed it. This is not a problem for me but thought I would mention the warping I see on one side of the cover.
Does anyone have any suggestions specifically for issue #1 where I cannot pull the filament sensor out of the main extruder assembly? If I can that part out, I may not need to worry too much about the connector potting (#2) hurdle.
John
The Sensor can be a little stubborn, the first time I removed it I used a tiny flat-blade and asked forgiveness after. It should be ok to look down the bore and see if there is anything obvious while its in place so don’t trouble yourself too much. The metal activation arm should move freely, you can use a bit of filament to check.
The white sealant is a bugger to remove, it can be worked away with the handy flat-blade again. Some people suggest a little heat to soften it but I did mine cold and it worked.
As for the cover, if its defective try sending a support ticket in and follow their lead.
The fail to retract can be a few things, it looks like you’ve got most of the way diagnosing, the wiki is a great source of info.
Thanks for the reply. I did not try to force the filament sensor out of the extruder assembly. Instead, I used a flashlight to look through the filament path and it looked clean. dusted it even though there was no visible dust or filament bits to be seen. I also blew out the path with an air-brush compressor.
I decided not to disconnect the filament sensor cable since I had already done the cleaning and everything looked clean. I simply reassembled everything and powered up the printer. (The printer only has about 60 hours of print time on it and about 30% of that was using PAHT-CF. The rest has been split between PLA and PETG.)
Now I seem to be chasing ghosts. I am now getting an error message to pull out the filament that is in the external filament holder on the back. There is no filament there and never has been. Yet it wants me to manually pull back on that filament. It thinks I have PAHT-CF loaded from the back. I have not used that path but PAHT-CF was the last filament I printed from the AMS before all this started.
As a double check, I powered the printer down and disconnected the AMS cable and the AMS PTFE tube. I gently manually fed PLA filament in at that point until it appeared at the PTFE tube entrance on the print head. There was no resistance going all the way through. There were no short lengths of any other filament pushed through the system before the PLA came out.
That leaves the question: which and where is the sensor that thinks I should be pulling filament from to clear the external filament feed? Note: I do NOT have a “Y” adapter on this printer to be able to use both the external feed and the AMS. I have only ever used the AMS.
John
WRT filament from the external spool holder, I had that error when I did not properly complete the unloading cycle. Manually feeding filament from the external spool holder all the way to the extruder, using the display to extrude a little bit of filament and then running the unloadibg routine as per display instructions resolved it.
Thumbs pressed and 
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Eno
Eno,
That seems to have done the trick. 
Thanks!
I disconnected the AMS and loaded filament via the external spool. It extruded a bunch of filament, cleaned the nozzle and waited. I then asked it to unload the filament. It cut the filament and then asked me to pull it back via the external spool. After doing so, all of the error messages went away.
Since I was doing other maintenance, I lubricated the lead screws and am now running a full machine calibration. Everything seems to be working.
After calibration finishes, I will power down, reconnect the AMS and run a couple of test prints to make sure the AMS is also clear. I think I already had it clear but who knows, I may have missed something since I am still pretty new to the world of 3D printers.
Thanks again for the clear instructions for getting the filament sensor back in sync with everything else.
John