Custom Snapmaker U1 Firmware

Faulty Toolhead Bypass

This firmware adds a Firmware Config recovery option for Snapmaker U1 printers that hit error 0003-0523-0000-0002 because one toolhead thermistor is faulty.

It is based on Snapmaker’s official guide:

• https://wiki.snapmaker.com/en/snapmaker_u1/troubleshooting/bypass_a_faulty_toolhead

Warning

This bypass is only intended to let the printer boot and keep using the remaining toolheads until the damaged part is replaced.

• Do not heat or print with the faulty toolhead while the bypass is enabled.
• Disable the bypass again after the repair is complete.

Configure

1. Enable Advanced Mode on the printer screen.
2. Open http://<printer-ip>/firmware-config/.
3. Go to Settings -> Troubleshooting.
4. Use the row for each affected toolhead: Faulty Toolhead 1, Faulty Toolhead 2, Faulty Toolhead 3, or Faulty Toolhead 4.
5. Change that row from Normal to Bypass Thermistor.
6. Firmware Config will restart Klipper automatically.

To undo it after replacing the faulty part, set each affected toolhead row back to Normal.

What It Changes

For the selected toolhead, the override:

• remaps the extruder temperature sensor_pin to PC5
• raises the extruder max_temp to 999
• sets the extruder max_power to 0.000001 because Klipper rejects 0
• sets the matching nozzle cooling fan heater_temp to 999
• sets the matching nozzle cooling fan fan_speed to 0
• changes the last stepped_temp_table entry from 260, 0.9 to 260, 0

Toolhead mapping:

• Toolhead 1 -> [extruder] and [heater_fan e0_nozzle_fan]
• Toolhead 2 -> [extruder1] and [heater_fan e1_nozzle_fan]
• Toolhead 3 -> [extruder2] and [heater_fan e2_nozzle_fan]
• Toolhead 4 -> [extruder3] and [heater_fan e3_nozzle_fan]

Implementation Note

Inference from the official guide and the stock U1 printer.cfg:

• The official guide says to change the temperature sensor pin suffix to PC5.
• Stock U1 configs use per-toolhead MCU pin names (e0:PA2, e1:PA2, e2:PA2, e3:PA2).
• This firmware therefore implements the remap as e0:PC5, e1:PC5, e2:PC5, or e3:PC5 for the selected toolhead.

The active override is installed into:

/oem/printer_data/config/extended/klipper/

Filename pattern:

• faulty_toolhead1.cfg
• faulty_toolhead2.cfg
• faulty_toolhead3.cfg
• faulty_toolhead4.cfg

Multiple faulty-toolhead overrides can be enabled at the same time if more than one toolhead is affected.