Error code 304 on the Elegoo Centauri Carbon 2 Combo is a Z-axis homing fault. The printer attempted to home the Z-axis but the photoelectric limit switch did not trigger at the expected position, which can cause the nozzle to continue descending and strike the build plate. Stop any ongoing homing immediately if you see this error mid-sequence.

What the Error Means

The Z-axis uses a photoelectric (optical) limit switch to detect when the carriage reaches the home position. Error 304 fires when the firmware commands a home and the switch signal never changes state — meaning the optical beam is either unbroken when it should be blocked, broken when it should be clear, or the switch is not sending any signal at all. Causes include a loose or damaged limit switch cable at either the switch end or the motherboard port, a physically misaligned or damaged photoelectric switch, and a faulty Z-switch input port on the motherboard. A related symptom is the nozzle descending without stopping, so monitor the first homing attempt closely.

Step-by-Step Fix

1. Command the printer to home the Z-axis and watch the behavior. If the nozzle moves toward the bed and shows no sign of stopping, press the emergency stop on the touchscreen immediately to prevent a bed crash.
2. Power off the printer and unplug it from mains power.
3. Remove the 16 screws securing the back cover using a 2.0 mm Allen key, then lift the back cover away from the frame.
4. Locate the Z-axis photoelectric limit switch cable and the Z-axis motor cable on the motherboard. Disconnect and firmly re-seat both connectors.
5. Inspect the switch cable along its length for cuts, kinks, or damaged connector pins. Replace the cable if any physical damage is visible.
6. Restore power and navigate to the printer’s diagnostic menu (or use the homing command). Watch the LED indicator on the motherboard at the Z-switch port — if it illuminates when the carriage physically blocks the switch beam, the port is functioning correctly.
7. If the port indicator works but the error persists, the photoelectric switch itself has failed. Replace the Z-axis photoelectric limit switch and cable assembly, then re-home to confirm the fix.

Parts Required

• Z-axis photoelectric limit switch and cable (replacement, if switch is faulty)
• 2.0 mm Allen key

If error 304 remains after replacing the switch and reseating all connectors, the Z-switch input port on the motherboard may need replacement — contact ELEGOO support for further guidance.

Frequently asked questions

What does Elegoo 304 mean?

Error code 304 on the Elegoo Centauri Carbon 2 Combo is a Z-axis homing fault. The printer attempted to home the Z-axis but the photoelectric limit switch did not trigger at the expected position, which can cause the nozzle to continue descending and strike the build plate. Stop any ongoing homing immediately if you see this error mid-sequence.

How do I fix Elegoo 304?

Error 304 on the Elegoo Centauri Carbon 2 Combo means the Z-axis homing switch is not triggering. Reseat or replace the photoelectric limit switch and cable to restore normal operation.