Centauri Carbon 2: leveling fails with error 704 or 605 (bed pressure sensors)

Symptom

During auto leveling, the Centauri Carbon 2 stops with error 704 («Leveling failed») or 605 (pressure sensor data error); sometimes the nozzle probes the same spot again and again or keeps pressing down on the bed.

Likely causes, from most to least likely

1. The printer stands on an unstable or tilted surface, or on a table with wheels.
2. The bed is tilted: the three Z-axis mounting blocks are not at the same height.
3. Z-axis homing fails: if the error appears while homing, it is a Z-axis problem (error 304).
4. A bed pressure sensor cable is loose.
5. A pressure sensor or the strain gauge adapter board is faulty.

Checks to tell which one it is

• Note when it appears: during Z-axis homing (check the Z axis first) or during leveling.
• Press the four corners: the printer must not rock; if in doubt, test it on a hard floor, not on carpet.
• After homing from Home, compare the gaps between the three Z-axis mounting blocks and the bed brackets: they must be equal.
• Note where the nozzle stops or presses down: it helps to find the faulty sensor.

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

1. Put the printer on a firm surface

   Place it on a flat, stable surface with no wheels. If you are unsure, repeat leveling with the printer on the floor.

   Check: Leveling completes without error.

   If that does not fix it: Check the Z axis and the bed tilt (next steps).

2. If Z-axis homing fails (304)

   If the nozzle strikes the bed while homing, Elegoo points to the Z-axis optical limit switch; if the Z axis jams or does not turn, to the motor, its cable or the mainboard. With the printer off and unplugged, remove the back cover (16 screws, 2.0 mm key) and reconnect the Z motor cable on the mainboard.

   Check: Homing completes without knocks or jams.

   If that does not fix it: If it persists, Elegoo suggests swapping the Y and Z outputs on the mainboard to tell whether the motor or the board is faulty; with that result, contact their support.

3. Level the bed by hand if it is tilted

   With the printer off and unplugged, remove the bottom cover (ten screws, 2.0 mm key), loosen the Z synchronous belt tensioner, remove its spring and take the belt off; press the bed down until the three Z-axis blocks sit flush with the bottom, then refit the belt and tensioner. Then adjust the lock nuts under the bed with a sheet of paper, at the centre and the four corners, as in Elegoo's guide.

   Check: The three gaps are equal and the paper drags the same at the centre and the corners.

   If that does not fix it: Run auto leveling again (Settings → Calibration → Auto Leveling); if the error persists, check the sensors.

4. Reconnect the pressure sensors

   Switch off and unplug. Remove the six screws holding the bed and the PEI plate; hold the pin of each locking bolt with a 2.0 mm Allen key, remove the four collars with another, lift the bed and reconnect the sensor cables.

   Check: Leveling completes without 704 or 605.

   If that does not fix it: Find the faulty sensor (next step).

5. Find the faulty sensor

   If the nozzle always stops or presses down at the same spot, swap that pressure sensor with the adjacent one on the same side, cables included, and level again.

   Check: If the stopping point moves, that sensor is faulty; if it does not move, the strain gauge adapter board is.

   If that does not fix it: Order the faulty part from Elegoo; if in doubt, send them a video with the error, the print head and the bed in view, the serial number and the firmware version (Settings → About Printer).

Prevention

• Keep the printer on a firm, level table without wheels.
• If the first layer comes out uneven or the bed looks tilted, level it by hand before running auto leveling again.
• Clean the PEI plate and seat it flat before leveling.

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Printers it applies to

Elegoo Centauri Carbon 2.

Official sources

This guide summarises the official documentation linked here:

• Error Code 704 (Centauri Carbon 2 Combo) · Elegoo
• Error Code 605 (Centauri Carbon 2 Combo) · Elegoo
• How to manually level the heated bed (Centauri Carbon 2 Combo) · Elegoo
• Error Code 304 (Centauri Carbon 2 Combo) · Elegoo