Anyone have a Toolhead Front Cover Has Fallen Off fault that was false. If yes, was it random or at same step in print process?
I’m getting one after the print is technically complete but toolhead is not completely parked yet.
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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.
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You are talking the Middle Housing correct? Front housing being held on by magnets but rear uses screws also.
One thing to be aware of is that there is a distinct possibility that Toolhead Front Cover Has Fallen Off is a catchall for any number of faults on the frontside hardware of the Toolhead. That toolhead is jam packed with circuits and I am on printer #2 because support could not find a bad board. I’d rather my printer would work than go through a board swapping exercise.
Back when my first printer started doing this same fault, but up front at PRINT START I got in this back and forth about the problem was MANIFESTING itself as a toolhead fault even though there was no real TOOLHEAD fault. That’s an important point to remember, Manifesting as X is different than Is X
Software has bugs and I think the definition of a bug is that it does something unexpected. So, getting these Front Cover has Fallen Off faults is bug behavior so you don’t necessarily want to take it too literally.
Think about it, I’m on printer #2 and it is manifesting the same fault. Different period in the print sequence…but same fault on two printers??
The upside for me as an owner is this is Bambu Lab code on Bambu Lab hardware. The software manifesting as Toolhead Has Fallen is pure, 100% Bambu Lab code.
I’m not sure I fully follow your point. Are you suggesting this is essentially a software ghost, where the error message doesn’t reflect the actual fault? If so, that’s definitely possible and supports my earlier point that this could all be resolved with a firmware update. However, it doesn’t change the practical remedy.
To expand on my theory, when I mention the Toolhead being stressed, I’m referring specifically to the circuitry inside it. The PCBs and cables have already been replaced, so that leaves us with a mechanical misalignment that might be triggering an incorrect error message.
I found that I would get random “The cover has fallen off” alerts on my PS1 when I had certain items plugged into the control board USB socket. I didn’t ever really dig into finding out what was causing it as I stopped using that port to power a LED thermometer and haven’t had a problem since.
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Yes to the software ghost. What JonRaymond said.
That Hall switch is miniscule and during the troubleshooting effort that resulted in sending me a new printer and shipping the problem printer back, I ultimately replaced every single part in the toolhead.
You ain’t living until you try and make a video of the Hall switch magnet moving on the hall switch associated with the filament runout/break detection…
Here is Hall switch that triggers a Real fault
This is the TH Board that Hotend, Extruder, Cover all plug into. The socket I have circled in green, Wooo-Weee that socket, 4 of them will fit on your thumbnail. The board that cable plugs into is on the side of the extruder and a little bit bigger than your thumbnail.
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For my “spoof” attempt. Here is where I tried to place the magnet. These two parts are the actual parts that I replaced. The magnet is one of two sizes I tried. It had no effect which lead me to initially believe the hall sensor was faulty.
Alternate view of the middle housing.
Zoomed in view.
A better view.
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Mine was significantly lower tech.
I took clear packing tape, the stuff that is about 2" wide, taped the front cover, middle cover, and back cover together to insure zero movement.
I’ve always heard that the basic definition of a software bug is when the code written exhibits unexpected behavior.
From my perspective, when the cover and its magnets are incapable of moving yet you consitently get a movement fault, you’ve got buggy software.
To me just another argument in favor of ditching these tiny connections and in the case of the cover, maybe a direct contact spring loaded limit switch
I would concur. Hall sensors have their place. Especially when one is talking about non-contact sensing such tracking the belt or an index wheel on a printer. In that use-case, its perfect because one can produce a tracking mechanism on a moving object without designing more mechanical parts. However, in the case of a cover switch, there is no advantage, just downside. A limit switch is exactly the right solution for the right problem.
Its precisely these sorts of design decisions that make one wonder what was going through the designer’s minds when they came up with this.
I know the answer to that one.
It’s cool and neato tech. Won’t be the first or last time I’ve seen things implemented for no other reason than it is a neat solution.
I bet Bambu Lab has spent a chunk of money on this particular bleeding edge tech that they didn’t need to spend.
I just sent a second reply asking What next? as in their first reply, they wanted my address so they could send spare parts. Last time that happened a couple of days later a UPS box full of parts showed up.
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Interesting.
MT9105 hall sensor (in used) is a linear one, which output is analogue voltage depends on magnetic flux strength. This device graded as 5V5 max, so it’s likely to run @3V3, sharing the power rail off the controller on toolhead board.
This hall sensor was set to detect magnetic flux change from 1 magnet to 2 stacking magnets.
I agree possible firmware fix can remedy this problem by reduce the detecting threshold voltage output of the hallsensor. Like, 2V threshold down to 1.8V threshold for example.
I suspect that power glitch produced by your led strip got into the output of the sensor somehow and upsetted it a little bit. But not really sure if this was the case.
In another thought, neodymium magnet starts loosing it’s magnetic strength when heating up to or over 80deg C. This effect is permanent. I think this could be the case.
Side story: I learned this hard truth when putting neodymium / hallsensor inside motorcyle engine.
You can upgrade to my solution, I use zip ties lol. I click it as tight as it will go and cut off the extra. Make sure the connector is on the lidar side so it won’t hit anything. They are super tight but you can still slide it off the bottom and slide it back on if you need to take the cover off.
No Lidar on a P1S but the more I wrestle with this fault, the more I think it is a catch-all for a multitude of faults.
My first printer, it gave me the Front Cover fault which was bogus, but before the printer ever started melting plastic so I was dead in the water.
This is after the print has completed and even the Wiki alludes to the possibility it is spurious because in the troubleshooting they say it may be spurious and so, reset it and see if it will start back printing.
Hard to read parts but
240/240 layers, time left -0 minutes, Even says Finished and the toolhead has retreated back to its “Parked” position. Total pain because you have to intervene to close-out the print and get it to 100% which is also permission to print.
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There definitely appears to be some interaction with the USB port inside the front of the printer. I have been getting these errors consistently but only on one 1 printer. I had one of those Big Tree Tech screens plugged into the printer that was failing. I just removed it and suddenly my printer started working and there so far have been no more reported toolhead cover issues
Welcome to the community!!!
The USB port on the printer has only two wires connected: +5VDC and GND. In short, it functions solely as a power outlet, nothing more.
The description you provided is consistent with a device that is either drawing too much power and/or causing feedback on the ground plane. However, it is inconclusive whether the fault lies with the device itself or the printer’s interface panel, which may have a faulty ground or power connection. Diagnosing this can indeed be tricky.
To simplify, the USB 1.0 and 2.0 specifications call for a standard 5 volts at 1 amp, equating to 5 watts of power. While some implementations provide more power, they technically violate the spec.
Tests you may want to consider
If you’re curious to investigate further, it would be valuable to perform some simple tests and share your results with the community. Here are the recommended tests:
- Test the device with a separate power source
- If possible, connect your device to a separate USB power source to verify that it functions correctly.
- Test with a different USB cable
- Use a different USB cable, ensuring it works with a known power source, then retest with the new cable. USB cables are notoriously inconsistent in quality.
- Use a USB power tester
- Purchase an inexpensive USB tester for more detailed diagnostics.
- Steps:
- Plug the tester into the USB port using a short USB extender for visibility.
- Connect a known device that consistently draws power, such as a USB light.
- Record the power draw when the light and tester combo are plugged into a known, functioning USB power source.
Sharing results from your tests would be greatly appreciated and a benefit to the community in understanding and resolving similar issues. 
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Recommended USB Power meters that are too useful and too cheap to NOT have in one’s tool bag.
Click here for links and photos to recommended USB Testing devices
Although anyone who knows how to use a multimeter can perform the tests that these devices use, these devices are easy and convenient and small enough to even keep on a keychain.
Here are the devices I use, they provide so much utility and are so cheap, I keep a couple on hand precisely for diagnosing issue USB power issues. I think I have one in every drawer of my office and shop. 
These tools reveal many of the Sins the USB power connector often has. 
The RuiDeng (RD Tech) UM25C USB Meter Tester(first sold around ~2016) is the granddaddy of all the USB power meters.
This meter is made by over a dozen Chinese makers under different brand labels and can be had from anywhere between $10-$30 depending on whether you buy them from Ali Express or Amazon. The original was Blue but other colors(Yellow & green) have things like USB-C and Power Delivery or Bluetooth interface to display and record results on your phone.
They all have the same recognizable plastic housing and are easily recognizable(see photo).
Although I have much more expensive versions of these testers, I recommend this one in particular because it has the simplest functionality and is the easiest to use. My other testers are more robust but require more technical knowledge, this is one even my wife can operate. 
A good alternative is this MakerHawk device which is even simpler and cheaper. The point is, just get something(anything) that will give you a readout, it doesn’t have to have five 9’s of precision either.
https://www.amazon.com/dp/B07FMQZVW2/
You’ll need a “Known” Device to Draw Power
The second thing you will need is something to draw power that is not the device you are testing. Remember: Power is not pushed, it’s drawn and something has to be in the circuit drawing power for the meter to measure. The device you choose will serve as your reference device, but it must have a constant power draw with no variability such as dimmers or switches. I use simple USB lights. Here are two variants that I keep in my toolbox for this purpose.
There have been other reports of aftermarket devices tapping power from that and generating a fault.
Installing the Biqu LED light has caused problems.
Seems like there is very little, if any free power available from that device with the USB port and so it is probably dragging down the voltage and causing phantom faults if I remember that members comment correctly.
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Presently going through this issue on a P1S with 518 hours on it. Bambu was quick to send out the TH Board, Extruder Connection board and FPC Cable in an effort to remedy the problem. However, upon installation of the new parts the problem persists. I can’t start a print and the head will stop in the Park position. I have triple checked all connections /screws and all appear to be correct. I then found this post and tried the suggested solutions mentioned with no luck. Presently waiting to hear back from Bambu as to how to proceed. It is possible I am overlooking something or have incorrectly installed the parts. If I find a solution I will post the results.
I wish I could give an easy fix but if you read the post from the beginning this particular post, which I initiated, was when the print was technically complete at between 96% - 99%. I would clear the alarm, click the arrow and print progress would go to 100%. Lather, rinse, repeat. I ditched the BIQU light and problem went away.
But very early in my Bamnbu Lab printing adventure I had exactly what you describe. Right down to inability to even start a print and including that business with it going to the park position.
Word of advice, if you have a decent build plate on printer, take it off and replace it with one you can stand to damage.
Ultimately, after spending about 5 - 6 weeks trying to resolve the problem they took my printer and sent me a new one. I hope you kept the shipping box.
Unfortunately, they were unable to fix the problem by swapping out the various parts of the toolhead.
The repeatability/consistency of the fault, when it would happen, the park business, everything screamed software/firmware problem. But because of their desire to keep their proprietary software proprietary you are unlikely to see some email with a flash file/update as an attachment.
They would rather send a new printer.
It pretty much was a pain in the behind to get a single email each day for a month telling me “Try this” when it did not help.
I would suggest, in the off chance that you have some accessory that pulls current that you added, take it off. The second time I had the “Cover has fallen” I think it was due to the BIQU light pulling power from board behind the touchpad.
I just started having the “cover off” problem after adding their Panda Touch screen. I’m going to try powering it externally and see if it stops happening.
Yes, I had to replace the toolhead and mothboard (where the toolhead plugs into it).
My nozzle got bent, my new 0.6 hardened…
Only got the first 3D printer (P1S) in November 2024, and this was 2 weeks ago…
I got my printer from 3D Prima Technology UK LTD, and they sorted it out with Bambu for me… But my nozzle I got from Bambu said it was a usable part, so I could get a replacement for it… But 3D Prima Technology UK LTD was quality and sorted it out for me…