<p>I've just changed the motherboard on my Ender 3 Pro with a MKS GEN_L v1.0 and flashed the latest Marlin version on it.</p>
<p>I've calibrated my bed manually using the default XY and Z auto home commands on OctoPrint and a piece of paper.</p>
<p>I'm happy with the calibration, however whenever I launch a print the Z axis moves up from the calibrated position by about 4 mm and starts extruding.</p>
<p>I've checked my Z endstop status with <code>M119</code> and it's triggered at the right calibrated position.</p>
<p>How can I correct this?</p>

[{'answer_id': 15506, 'author': 'octopus8', 'author_id': 26170, 'author_profile': 'https://3dprinting.stackexchange.com/users/26170', 'pm_score': 0, 'selected': False, 'text': '<p>If you are already sure that homing is performed correctly and in valid position, then there are few reasons why printer may start printing in unexpected position.</p>\n<p>Do the following checks to narrow down the actual one:</p>\n<ul>\n<li><p><strong>steps/mm</strong>: use <a href="https://marlinfw.org/docs/gcode/M503.html" rel="nofollow noreferrer"><code>M503</code></a> (or <a href="https://marlinfw.org/docs/gcode/M092.html" rel="nofollow noreferrer"><code>M92</code></a> without parameters) to check if currently configured steps/mm match <a href="https://blog.prusaprinters.org/calculator_3416/#steppermotors" rel="nofollow noreferrer">your hardware setup</a> for each axis</p>\n</li>\n<li><p><strong>offsets:</strong> use <a href="https://marlinfw.org/docs/gcode/M503.html" rel="nofollow noreferrer"><code>M503</code></a> (or <a href="https://marlinfw.org/docs/gcode/M206.html" rel="nofollow noreferrer"><code>M206</code></a> without parameters) to check that there are no offsets configured</p>\n</li>\n<li><p><strong>backoff:</strong> look in <em>Configuration_adv.h</em> for following line:</p>\n<pre><code>//#define HOMING_BACKOFF_POST_MM { 2, 2, 2 }  // (mm) Backoff from endstops after homing\n</code></pre>\n<p>(Having the backoff set is nothing wrong, actually. But be sure to also check final positioning in the generated file.)</p>\n</li>\n<li><p><strong>slicer\'s Start G-code:</strong> review slicer configuration, if there is nothing suspicious injected to the print file, which could temporarily overrid printer setup - esepecially <a href="https://marlinfw.org/docs/gcode/M428.html" rel="nofollow noreferrer">M428</a>, <a href="https://marlinfw.org/docs/gcode/M206.html" rel="nofollow noreferrer">M206</a>, <a href="https://marlinfw.org/docs/gcode/G092.html" rel="nofollow noreferrer">G92</a> <em>(set position is normal for E in relative extrusion mode, but suspicious for X,Y,Z)</em></p>\n</li>\n<li><p><strong>generated file:</strong> review initial part of generated G-Code file, if there are any similar surprises, and if on initial layer section there is expected move to valid Z position before extrusion is made</p>\n</li>\n</ul>\n'}, {'answer_id': 15516, 'author': 'Pierre', 'author_id': 26601, 'author_profile': 'https://3dprinting.stackexchange.com/users/26601', 'pm_score': 3, 'selected': True, 'text': "<p>I've actually found what the issue was. It turns out that my Z steps were way out of whack (i.e. 4000 steps/mm instead of 400). Apparently, that's the default value in GitHub for version 2.0 of Marlin. Not sure if that's a typo or a valid value, anyhow setting it to 400 fixed it.</p>\n"}]
['https://3dprinting.stackexchange.com/questions/15503', 'https://3dprinting.stackexchange.com', 'https://3dprinting.stackexchange.com/users/26601/']