The Neptune 4 Plus runs the same customized Klipper firmware as the rest of the Neptune 4 lineup. Elegoo’s own wiki states plainly that “the Neptune 4 series uses the Klipper system” and warns that flashing firmware through Fluidd instead of Elegoo’s own repair packages “will brick your printer,” since the board runs a locked-down, non-standard Klipper build rather than stock Klipper. This article draws on Elegoo’s wiki pages filed under the Neptune 4 Plus product entry and its shared troubleshooting pages with the Neptune 4 Max. That sharing turns out to be the most important fact about this printer’s error system: most of the fault pages are literally titled “Neptune 4 Plus & Neptune 4 Max,” meaning Elegoo treats the two large-bed variants as one troubleshooting surface rather than writing separate documentation for each. Where the Plus differs from the Max on the wiki’s own index, it is mostly a difference in which pages got linked from which product page, not a difference in actual bed size or heating behavior.
MCU shutdown and thermal faults
MCU mcu shutdown: ADC out of range appears when a heater’s reported temperature exceeds its configured minimum or maximum limit, which Elegoo attributes to an abnormal reading between the hot end and hot bed thermal sensors, most often a damaged thermistor. The documented fix sequence: power off and reseat the connector in the affected area, wait about a minute before powering back on (this can clear the fault on its own), check for bent pins on the connector, inspect the hotend and bed thermal wiring for damage, and if the bed wiring is the suspect, move the bed to reduce cable bending in that area and see if the fault clears. If none of that resolves it, Elegoo’s page directs users to check the nozzle and bed temperature readings through the printer’s Klipper web interface (Fluidd) and to submit a photo if the nozzle temperature displays as negative.
Heater extruder not heating at expected rate is documented on the combined “how should I do with these error messages” troubleshooting page for the Plus and Max. Steps include confirming the printer’s voltage switch is set correctly (with the power off and unplugged before adjusting it), checking the ceramic heater plug and the adapter board pins for looseness or damage, and checking the mainboard’s ceramic heater wiring. If all of that checks out, Elegoo says the hotend, extruder cable assembly, or adapter board need replacing.
Please run ‘SDCARD RESET FILE’ or ‘FIRMWARE RESTART’ to resume.!! Extrude below minimum temp is caused, per Elegoo, by either an inappropriate slicer setting on the model file or a damaged or loosely connected extruder thermistor cable. The fix path is to reprint the bundled test file (or re-slice with Elegoo Cura or Elegoo Slicer’s default settings) first, and if that doesn’t help, physically open the extruder to check and reseat the thermistor cable’s pin connection.
Stepper driver faults
TMC stepper_y reports error: DRV STATUS: 401b0103 otpw=1 (OvertempWarning!) can show up on the touchscreen during printing or immediately after power-on. Elegoo’s steps: re-flash the firmware to restore default motor current settings (in case those were altered), loosen the X/Y belt if it’s over-tightened, check whether the Y motor plug is loose or damaged, and check whether the mainboard’s chassis-bottom cooling fan is spinning (that fan only starts once the nozzle hits 50 degrees C).
TMC stepper_y reports error: DRV_STATUS: 801900e0 s2vsb=1 (LowSideShort_B) points to poor contact at the Y motor connector or a damaged Y motor, cable, or mainboard. Troubleshooting has you check the connector on both the motor side and the mainboard side, then, if unresolved, swap the X and Y motor connectors as a diagnostic: if the error follows the motor to the X axis, the Y motor and cable need replacing; if it stays on Y with the swap in place, the mainboard needs replacing.
TMC stepper_z reports error DRV_STATUS40190010 s2vsa=1 (LowSideShort_A!) follows a similar diagnostic pattern for the dual Z motors: reseat the connector at the Z motor and at the mainboard, then disconnect one of the two Z motors at a time and jog Z from the touchscreen’s Prepare menu to isolate which motor or cable is at fault, or confirm it’s the mainboard if the error persists with both disconnected.
TMC Stepper_X / Y 00000002 drv_err=1, documented on the combined troubleshooting page, is addressed by powering off and checking whether the X-axis motor plug is loose or damaged, then reseating it.
TMC Extruder…lowside short (also from the combined page) is resolved the same way: power off, then check whether the extruder plug at the marked position is loose or damaged.
Input shaper and accelerometer faults
Y axis vibration detection failed / Y-axis sensor status is abnormal, and on Fluidd the equivalent Failed to set ADXL345 register / !! invalid adxl345 id, occur during input shaper calibration. Elegoo lists four causes: a loose Y-accelerometer connection, a damaged accelerometer or cable, the printer not having been restarted after a firmware update, or mismatched motherboard and touchscreen firmware versions. The documented steps: power off and check/reseat the Y-accelerometer cable, restart the printer if firmware was recently updated, and verify the motherboard and touchscreen firmware versions are a matched pair (Elegoo publishes a specific pairing list, for example mainboard v1.2.2.64 with touchscreen UI 1.2.11, v1.2.2.65 with UI 1.2.12, and so on through v1.2.3.2). If none of that clears the fault, the page says the Y-accelerometer or its cable likely needs physical replacement.
X-axis vibration detection failed / X-axis sensor status is abnormal follows the same troubleshooting shape: reseat the extruder cable (straightening any bent pins), reconnect the input shaper port plug on the motherboard side after removing the bottom cover, restart after any firmware update, and check firmware version compatibility using the same pairing list as the Y-axis fault. Elegoo attributes lingering cases to a faulty extruder cable or the adapter plate where the accelerometer sits.
Print job and G-code faults
Several fault messages are documented as spanning the entire Neptune 4 family, not just the Plus and Max, and Elegoo’s own pages say so explicitly by listing “Neptune 4, Neptune 4 Pro, Neptune 4 Plus, Neptune 4 Max” under the page title.
Please run “SDCARD RESET FILE” or “FIRMWARE RESTART” to resume. Extruder not configured is attributed to model files sliced by unofficial software or insufficient memory in Fluidd. Fix steps: print the bundled USB test file to confirm the printer itself is fine, re-slice with Elegoo Cura or Elegoo Slicer’s default settings, and check Fluidd’s storage and delete unnecessary G-code files if space is tight.
Please run ‘SDCARD RESET FILE’ or ‘FIRMWARE RESTART’ to resume,!! Move exceeds maximum extrusion stems from selecting the wrong printer profile when slicing, or not enabling relative extrusion in the slicer. Elegoo’s fix: confirm the printer type against the SN sticker on the bed (NEP 4, NEP 4 Pro, NEP 4 Plus, or NEP 4 Max), correct the slicer profile if it’s wrong, enable relative extrusion, and update to the latest firmware if the problem persists.
Please run ‘SDCARD RESET FILE’ or ‘FIRMWARE RESTART’ to resume.!! Unable to parse move is blamed on a corrupted G-code file with illegal characters, or an abnormal firmware configuration file. The fix path is to print the bundled test file, re-slice with default settings and an all-ASCII filename, and update the fix pack plus motherboard and touchscreen firmware if the test file also fails.
MCU mcu shutdown Rescheduled timer in the past and MCU mcu shutdown invalid oid type are both attributed to third-party plugin installs overloading the MCU or incorrectly modified firmware settings. Both are addressed the same way, by reloading the fix pack and updating motherboard and touchscreen firmware together (Elegoo links separate instructions for the Neptune 4/Pro pair versus the Plus/Max pair, since the repair packages are model-specific downloads). The invalid OID type page also recommends reinstalling the eMMC image file if firmware reflashing doesn’t resolve it.
MCU rpi shutdown: Unable to open spi device shows up on boot along with an inability to reach the system interface, and Elegoo attributes it to firmware that was incorrectly burned or is missing entirely. The fix is a full re-flash using the model-specific repair and firmware packages; Elegoo’s download page lists a distinct Neptune 4 Plus repair package (Neptune 4 PLUS_1.2.2.65_1.2.12) separate from the Neptune 4 Max one, even though the troubleshooting steps read identically.
“SDCARD_RESET_FILE” and “SD Card reset”, from the combined troubleshooting page, both trace back to slicer configuration problems (wrong printer profile selected) or a damaged proximity switch or breakout board connection. Fixes include reslicing with Elegoo Cura’s defaults, updating firmware, checking connector pins for damage, and checking the proximity switch plug. If hardware is confirmed faulty and the printer is under warranty, Elegoo will issue a replacement breakout board, proximity switch, and extruder cable.
Timer to close, shown during printing, is attributed to third-party plugins overloading the mainboard, incorrectly modified firmware settings, or a corrupt G-code file. Elegoo’s fix is to update the fix pack plus motherboard and touchscreen firmware and reprint, and if the error recurs, to send Elegoo support the printer.cfg, klippy.log, and moonraker.log files pulled from Fluidd along with the SN code and the G-code file that triggered it.
Connectivity and firmware faults
Internal error during connect – can’t convert negative number to unsigned appears immediately on power-on, either on the touchscreen or in Fluidd. Elegoo’s stated cause is installing firmware not provided by Elegoo, since flashing through Fluidd (rather than Elegoo’s own repair/motherboard/touchscreen packages) can brick the board; third-party firmware carries the same risk. The fix is to reflash using the official repair package, motherboard firmware, and touchscreen firmware, and if that fails, reinstall the image file via eMMC adapter.
Connect moonracker timeout (Elegoo’s own spelling of “Moonraker”) is addressed with the same repair-firmware-then-mainboard-and-touchscreen-firmware update sequence as the MCU shutdown fault above.
HTTP 500, seen specifically when uploading a file to the printer through OrcaSlicer, is attributed to network instability. Elegoo’s suggested fix is changing “localhost” to “0.0.0.0” in moonraker.conf via the web interface and retrying.
Touchscreen stuck on loading screen / motherboard firmware version missing is linked from the Neptune 4 Plus error code index, though the page itself is titled for the Neptune 4 and Neptune 4 Pro specifically. Causes span hardware (damaged eMMC module, motherboard, or touchscreen; a short in an externally connected accessory like the USB drive, filament runout sensor, or gantry LED) and firmware (incorrectly modified settings, a crashed motherboard firmware, or an unofficial firmware install). The multi-step fix involves unplugging external accessories one at a time to isolate a short, reloading the fix pack, reflashing the motherboard firmware over USB-C if needed, reinstalling the image file, and as a last resort swapping the eMMC module, motherboard, or touchscreen.
The Neptune 4 Plus’s error corpus overlaps heavily with its Max sibling, since Elegoo documents many of these faults on shared “Plus & Max” wiki pages. See the Elegoo Neptune 4 Max Error Code Index for the handful of codes indexed only on the Max’s own product page.