HMS 1A00-1200-0002-0004: Hotend Rack Height Calibration Is Abnormal
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HMS 1A00-1200-0002-0004 means the height part of the rack calibration produced a result the machine will not accept, and Bambu asks you to check for foreign objects that may be causing the rack to jam. A rack that cannot complete its vertical travel measures a height that is not the real one.
Note that this is specifically height. The rack calibrates in more than one axis, and the code tells you which one failed.
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Clear the vertical travel, as asked
With the power off, move the rack through its height range if the mechanism allows and feel for the point where it stiffens. Debris that is harmless in one axis blocks another, which is why a rack that moves freely side to side can still fail this. Clear what you find with a pick rather than pushing it deeper, which is the same discipline the lock rod needs in HMS 1A00-1200-0002-0008.
Measure rather than guess
If the travel is clear and the result is still rejected, put numbers on it. A dial indicator on a magnetic base shows whether the rack sits where it should relative to its mounting, and a feeler gauge checks a gap you suspect has changed. Guessing at a height fault costs more time than measuring it.
Then the mounting
A rack that is straight but mounted loose settles under its own weight between calibrations, and the height it reports drifts accordingly. Work along the fasteners, tighten in sequence, and use medium-strength thread locker on any that keep loosening rather than more torque.
How HMS 1A00-1200-0002-0004 differs from an out-of-range result
An impossible number rather than an unacceptable one is HMS 1A00-1200-0002-0003, where Bambu suspects a deformed rack. This code is the gentler version: the measurement is wrong, not nonsensical, and jamming explains most of them.
After clearing it
Re-home, re-run the calibration in full rather than only the height step, and check a first layer before committing a plate. The camera-side failure is HMS 1A00-1200-0002-0001, and the general sequence is in calibrating a 3D printer.
HMS 1A00-1200-0002-0004 FAQ
Can I skip the height step?
No. Slot positions depend on it, and a wrong height is a collision rather than a bad layer.
What jams it vertically?
Purge fragments and printed debris that have fallen into the mechanism from above.
Do I need a dial indicator?
Not to clear debris. Only if the fault survives cleaning and you need to know by how much.
Could a firmware update help?
Occasionally, and it costs nothing to rule out first.
Two codes in this group carry identical wording. HMS 1A00-1200-0002-0009 is the second timeout code, and there is genuinely no difference in what you do about it.
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