The “MCU mcu shutdown: ADC out of range” message causes Klipper to halt the Elegoo Neptune 4, Neptune 4 Pro, Neptune 4 Plus, or Neptune 4 Max immediately. Klipper monitors every configured temperature sensor continuously, and when any reading falls outside its configured minimum or maximum ADC threshold, it shuts down to prevent uncontrolled heating or missed runaway conditions.

What the Error Means

ADC (analog-to-digital converter) out of range means that the voltage the MCU reads from a thermistor is below or above the expected range for any plausible real-world temperature. The most common cause is a thermistor that has completely disconnected or broken — an open circuit produces a rail-high voltage, which maps to a temperature far outside any valid range. A short circuit produces a rail-low reading. On the Neptune 4 and 4 Pro, the print head flat ribbon cable is the most frequent failure point: the ribbon cable carries both the hotend thermistor signal and the heated bed thermistor signal along the X-axis carriage, and flex fatigue or improper seating after maintenance causes these signals to drop out. A shorted heater element can also pull the ADC value out of range. On the Neptune 4 Plus and Max, the flat cable routing is different and requires the Plus/Max-specific disassembly approach documented in ELEGOO’s wiki.

Step-by-Step Fix

1. Power off the printer immediately and let all heated components cool before touching any internal wiring.
2. Locate the print head flat ribbon cable (the thin flexible cable that connects the print head to the main carriage electronics). On the Neptune 4 and 4 Pro, this cable runs along the X-axis gantry.
3. Re-seat both ends of the flat ribbon cable: the connector at the print head board and the connector at the X-axis carriage board. Improper seating is the most common cause of this shutdown on these models.
4. Re-plug the hotend thermistor connector and the heated bed thermistor connector at both the print head board and the mainboard. Even a slightly unseated connector produces an ADC fault.
5. Restore power and wait approximately one minute. Watch the Klipper web interface (Fluidd or Mainsail) for temperature readings — both the hotend and the bed should show a stable room-temperature value close to ambient.
6. If the shutdown recurs on the same sensor, the thermistor itself has failed. Replace the faulty thermistor (hotend or bed, whichever is showing the out-of-range reading) and re-run the check.
7. Neptune 4 Plus and Max owners should follow the Plus/Max-specific flat cable routing guide on the ELEGOO Wiki, as the disassembly sequence differs from the base Neptune 4.

Parts Required

• Replacement NTC100K hotend thermistor (if thermistor test fails)
• Replacement heated bed thermistor (if bed sensor is the fault)
• Print head flat ribbon cable (if cable is physically damaged)

Contact ELEGOO support if the ADC out of range shutdown recurs after replacing the suspected thermistor and confirming secure cable connections.

Frequently asked questions

What does Elegoo n4-adc-out-of-range mean?

The "MCU mcu shutdown: ADC out of range" message causes Klipper to halt the Elegoo Neptune 4, Neptune 4 Pro, Neptune 4 Plus, or Neptune 4 Max immediately. Klipper monitors every configured temperature sensor continuously, and when any reading falls outside its configured minimum or maximum ADC threshold, it shuts down to prevent uncontrolled heating or missed runaway conditions.

How do I fix Elegoo n4-adc-out-of-range?

Klipper's ADC out of range error shuts down the Elegoo Neptune 4 series when a temperature sensor reads outside safe limits. Reseat the flat ribbon cable or replace the faulty thermistor to restore operation.