I have been waiting for someone else to bring this up. Yes, I have been experiencing this issue.
For comparison, my issue is a little different than what you described but it is the same error. It was happening only half the time. In my case it occurred at the start of the print sequence during bed leveling. About 70% of the time, the error appeared after the nozzle homed, and snapping and unsnapping the tool cover remedied it. The other 30% of the time, the error happened while the printer was warming up, right when the nozzle was set to extrude the purge line. The same remedy worked there as well. It sounds like your error is happening at a different stage.
I have had this problem recently, July through October. And after spending over $78 in rebuilding the tool head, the problem did not resolve itself. This, with the help of Bambu’s tech support team. Totally worthless!!!
However, I can share at least partial success. Although I never got a straight answer from tech support—when do they ever give a straight answer—the disassembly of the tool head revealed a possible remedy.
I replaced the following:
Toolhead Middle Housing $9.99
Front Housing Assembly - P1 Series $19.99
Extruder Interface Board - P1 Series $9.99
TH Board - P1 Series $39.99
TH Board FPC Cable - P1 Series $7.99
After I replaced those and the problem continued, Bambu graciously sent me a Toolhead Middle Housing valued at $10. Which was the only thing I did not replace at that point. That did not fix the problem either.
Replacing the toolhead was a complete waste of money!!!
Possible Remedy
I had left the screws off the housings just so I could avoid stripping them during my trial and error. After 3 months, the problem spontaneously cured itself. So last weekend I took the screws I had left to the side for diagnostics and and after the printer appeared to be stable, I reinstalled them. On the very next print one minute later, “Toolhead Front Cover Has Fallen Off”. So on a hunch, I removed the screws from the middle housing but left the plastic in place. It has now been working fine for the last 5 days without incident, no thanks to Bambu Lab and my wallet being $78 lighter.
Possible Theory
The Toolhead sensor operates via a Hall sensor (magnetic switch). The magnetic tool cover is supposed to push enough magnetic flux forward to trigger the Hall sensor, confirming the cover is attached. When snapping the cover on and off seemed to reset the circuit, I initially thought it was a circuit board or cable issue. Wrong again. The real problem, I believe, is that over time the plastic tool head cover warps slightly. (Yes, I even tried installing a magnet inside the middle housing cover to spoof the Hall sensor—no effect.)
This is something that could be easily corrected with a firmware adjustment, but we all know Bambu’s stance on that: pound sand. My current theory is that leaving the screws off the middle cover reduces stress on the housing and mitigates the alignment issue.
Not that I can verify any of this, of course. The logs are encrypted, and Bambu refuses to grant access to the data. For now, I’m still testing, but the printer seems to be working—at least until the next issue rears its head.
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Suggestion to diagnose and fix this issue
While my experience is certainly not proof, it is an inexpensive and easy thing to try out. I might suggest that you remove the screws from the housing. If memory serves there are four in the back and four in the middle. Don’t worry that the cover will fall off, they snap in tightly and I had no problems. Try to momentarily unsnap the cover just to ensure that the covers are not sticking to the nozzle head thus ensuring that there is no stress on the housing. Then see if the printer issues that message again. If it doesn’t, then just leave the screws off. I placed them on a magnet so I wouldn’t lose them BTW and I suggest anyone trying this to do the same.
Good luck🍀and let the community know how you faired.