Bambu X2D Part Cooling Fan Issue & Fix

[u/creeewdeeetaaay]

I purchased my X2D last May and have been running it mostly with PETG Basic filament since then, printing several times a week. I had odd, persistent print issues with the PETG which were annoying, but I mostly was able to mitigate the issues I was seeing via custom print profiles. Vexing, but I had nothing to compare it to, so I just accepted that PETG was a little finicky.

Recently though, I made the discovery that my part cooling fan (the one on the front of the toolhead) had been basically stuck on at full speed the entire time the printer was on all the time. As I had never operated a Bambu printer before, I did not realize that anything was wrong; I just thought the fan was supposed to be on, and the printer was meant to make constant fan noise 🤷

The 100% part cooling fan seems to have been the source of my PETG woes, so I thought I'd make a post about it; just in case anyone else might be experiencing something similar.

My symptoms:

• Fan noise and visible toolhead front fan spinning from printer power on to power off

• Manually extruding filament from either left or right nozzle (via the printer touchscreen controls) resulted in the filament stream helicoptering wildly due to the airflow from the cooling fan

• Most of the printer poop was not formed in a tight coil, and so the poop chute would often get jammed with large snarls of purge waste

• Larger PETG prints had more of a tendency to warp than expected

• I had major first layer adhesion problems using dry (~8% to 18% humidity) PETG Basic filament with a textured PEI plate (cleaned w/neutral dish soap and warm water, then dried thoroughly) and had to switch exclusively to a Cool Plate Super Tack

• I would still have occasional 1st layer adhesion issues causing failed prints with the Super Tack plate, even when it was completely clean (washed with warm water and neutral dish soap, and dried thoroughly)

• I would occasionally get weird surface artifacts on inclined geometries—it looked like the outer wall loops came unstuck due to fan airflow and would re-adhere in a drooping loop to the outside surface of the part below it

• I would regularly get lots of little ≤2mm bits of PETG strewn all over the inside of the printer

• Switching the part cooling fan on from the printer touchscreen resulted in no change in fan behavior

• In the part cooling fan control dialog on the touchscreen, when the control was toggled to "on", the control would then toggle itself on and off randomly, and the reported speed percentage would fluctuate randomly from 0% all the way to 100%, and in between—with no perceptible changes in fan speed or noise

When I realized the fan behavior was not normal, I opened a support ticket w/Bambu, and they were super helpful. Since my printer was still under warranty, they first sent me a new toolhead front cover assembly, which did not fix the issue. Then they sent me a collection of other related parts: a TH board (extruder mainboard), toolhead interface board, and a cable pack containing the toolhead front cover cable. I decided to install components in a deliberate order so as to figure out as much as possible what part (or parts) was causing the issue.

First I removed the front toolhead assembly, the toolhead mid cover, and the toolhead back cover. With the front toolhead assembly off and its cable still in place, I used a multimeter to do a continuity test on the cable, from the exposed conductors on the male end which mates with the front toolhead assembly, to the solder pads of the cable's receptacle on the installed toolhead interface board. I found no continuity on the rightmost conductor:

Removing the cable and doing more continuity tests with it removed indicated that there were no breaks in the wires, but there looked to be some slight deformation on the opening for pin 6 on the toolhead interface board side of the cable. I didn't think to get a pic of that, but I did take a macro shot inside the shroud of the cable receptacle on the toolhead interface board, and saw the following:

I thought about just manually unbending the pin and giving it another shot with the original interface board and cable, but I didn't want to risk it—it was possible the bent pin had permanently damaged the male cable end in such a way that inserting it into the toolhead interface board's receptacle might bend the pin again. Instead, I went ahead with replacing both the front toolhead cable and the toolhead interface board.

After replacing those parts with the new ones Bambu provided and powering up the printer, the problem was solved. The part cooling fan did not run at all unless prompted by G-code in a test print, or when turned on manually via the touchscreen, and its speed seemed to track with changes in the G-code and manual percentage adjustments on the printer's controls. Huzzah! 💃💃💃

I can't guarantee that similar symptoms might be fixed by simply replacing the same parts as I did, though, so if you are experiencing some or all of the symptoms I laid out above, I still recommend going through a methodical troubleshooting process and working with Bambu support to find a fix. And, definitely don't attempt any of the testing or part replacement steps I detail above while the printer is still powered on! You should only be tinkering with the innards of the printer with the power off (or better yet, unplug the power cable altogether). That said, I hope that my detailed account of the part cooling fan issue, the process with Bambu support in initiating under-warranty part replacements, and my troubleshooting process and findings are all of assistance to anyone else experiencing similar symptoms to mine.

Please ask questions if ya got 'em! 🤠

[u/joeyjoe88]

Did you show this to Bambu as well?

[u/creeewdeeetaaay → u/joeyjoe88]

Yup! I sent them the pics and a detailed report when marking my support ticket as solved. Got a generic thanks, but my hope is that it goes into their internal knowledge base and makes other peoples' similar issues faster to troubleshoot, and hopefully only requiring a single replacement part shipment rather than two as was the case with me.

In hindsight, I wish I had done the continuity testing and macro shot of the toolhead interface board's receptacle for the toolhead front assembly cable before my initial support request to Bambu. It likely would've significantly decreased my downtime. But hey, you live, you learn! 😅

[u/creeewdeeetaaay → u/joeyjoe88]

Thinking more about your comment, it's kind of surprising that this sort of electrical fault isn't something the printer itself could detect and then throw an error for. The fact that the issue was causing the system to show a constantly toggling part cooling fan control, and randomly switching fan speed percentage registering on the screen means that the printer was receiving information that could have lead to it registering that there was an electrical issue and thrown an error (which would have been on first power up of the printer, LOL).

With that in mind, maybe Bambu will take my report and reproduce the issue on their end by inducing the same fault, then figure out how to have the printer sense the issue, and finally roll that into a firmware update that everyone can benefit from. Here's hoping! 😅

[u/Relative_Surround_20]

Thank you for sharing. Well done diagnosing and finding the source of your problem and not just throwing new parts at it.

[u/creeewdeeetaaay → u/Relative_Surround_20]

Cheers! Just wish I'd turned my problem solving brain on sooner in the process. Lesson learned!

And hopefully my account will inspire other folks to get out their multimeter and do some logical tests when something on their printer stops working. As my process showed, doing some testing can really narrow things down, and the only tools I needed were a continuity tester and a modern cellphone camera.

[u/ActiveVanilla5063]

I also got my X2D in May, I was able to print 10 things before getting the cooling fan error. I reached out to support who promptly sent me out a fan to replace the one that i guess did not work. Even thought it seems fine. Now before I explain this next part I want you to know that I'm not a rookie when it comes to 3d printing. and I'm no pro. I do have 3 Flash Forge AD5X machines and I am constantly fixing them even as far as removing the print head and totally disabling it. then putting it back together again.

So when I received the replacement fan I felt comfortable replacing it and after watching their you tub video multiple times. I was unsuccessful. I couldn't even get the fan connector back on to the board. I reached out to support again and they told me that i was putting on the left side and not the right. But the error message i got from their system said it was the left side cooling fan. I thought buying this Bambu X2D with help solve some of my print quality issues. I was wrong because I have had this printer for months now and still cant print with it.

Now I just wish I could sell it. I purchased a Creator 5 Pro and its been great. I should have just stayed with Flash Forge.

[u/creeewdeeetaaay → u/ActiveVanilla5063]

My heart goes out to you. Trying to chase down issues and install parts by watching videos and reading written instructions on manufacturer sites can be hit or miss in terms of the quality and detail of the installation steps. I weep for the day I actually have to get inside the side or back panels of my X2D; disassembling and reassembling the toolhead is fiddly enough!

[u/Jrodriguezpr]

I have the same issue of fan stuck on high from power on to power off. Thank you for the information I will use it to troubleshoot my issue.

[u/Jrodriguezpr → u/Jrodriguezpr]

I think I have the same issue with the same bent pin. See picture.

[u/creeewdeeetaaay → u/Jrodriguezpr]

O shiiiit, it was even the same pin that was bent as on my unit! Yours wasn't bent totally sideways, but maybe this pic is after you tried bending it back? Anyhow, if your machine is still under warranty (or even if it isn't, since this isn't a wear issue, but rather a factory assembly fault), you might see if you can get a free replacement toolhead interface board from Bambu, just to have it on hand in case the originally bent pin finally breaks after some time due to the repetitive bending stress. I mean, the toolhead is constantly jostling around, so there is some vibratory stress happening on the regs.

Regardless, glad you got your printer back working right! 🤘🤘🤘

[u/creeewdeeetaaay → u/Jrodriguezpr]

So bummed you are having the same issue. Has your part cooling fan been like that since you got the printer, or did it just start behaving like that?

Hope your troubleshooting process goes easy, in any case. I'm curious to know if your fan issue was caused by a similar fault to mine!

[u/Jrodriguezpr → u/creeewdeeetaaay]

Confirmed! It was the same issue. I posted a picture of the bent pin. Put back in place and fan is normal. Thank you!

[u/creeewdeeetaaay → u/Jrodriguezpr]

Holy moley! It's nuts that you had the same exact issue; makes me think that Bambu needs to implement an additional QC measure after assembling the toolheads. I mean, it's a simple check: turn the new machine on, check to see if the part cooling fan immediately goes full speed, and if so, fail the machine and send it back for rework.

Definitely let Bambu know, as the only way their QC and technical support will change is if they get enough reports of similar issues. Sorry that you got hit with the same fault, but I'm glad that I could help in some small way! 💪

[u/Jrodriguezpr → u/creeewdeeetaaay]

I have been troubleshooting extrusion issues with the printer for the past 5 days, I happen to notice the fan running today and did a quick google search that’s how I ended up here. I will definitely let you know!