Fan error: hotend fan running slow (0300-0300-…) or part cooling fan stopped (0300-0400-0002-0001)

Symptom

The printer warns that the hotend (heatsink) fan is slow or stopped, for example 0300-0300-0002-0002, or that the part cooling fan is slow or not spinning (0300-0400-0002-0001). With the hotend fan stopped, the heatsink heats up and the filament can soften and clog.

Likely causes, from most to least likely

1. Blades blocked by filament strings, dust or other debris.
2. Fan connector loose or badly seated.
3. Faulty fan or one fitted the wrong way round: the hotend fan has a correct orientation and causes an error if reversed.
4. Failed toolhead (TH) board or extruder connection board.

Checks to tell which one it is

• Remember that the hotend fan switches off below 50 °C and runs from 50 °C upwards: it is normal for it to be still with a cold nozzle.
• With the fan stopped, turn the blades slowly with a pen or screwdriver: they should spin without catching.
• Set the nozzle to 51 °C and see whether the hotend fan starts.
• On the X1, P1, P2S and H2 series, test the part cooling fan from Control → Fans → Part Cooling Fan.

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. Clean the blades

   Set the hotend temperature to 0 °C, turn the part cooling fan off from the printer and wait for the toolhead to cool. Remove the front cover (magnetic on the X1, P1 and P2S; on the H2 series follow the disassembly guide) and clear strings and dust with a pen or tweezers, keeping your fingers out.

   Check: The blades spin freely.

   If that does not fix it: Check the connector (next step).

2. Reconnect the fan

   With the printer off, unplug and firmly replug the fan connector (the hotend fan uses a 4-pin connector on the X1 and P1). Pull the connector straight out from the board without twisting it.

   Check: After power-on, the alert is gone.

   If that does not fix it: Check the toolhead board connection (next step).

3. Check the toolhead board (X1 and P1)

   Check the connection between the extruder connection board and the TH board; on the X1 with a V8 board, check whether the 10-pin connector is loose or damaged and reseat it.

   Check: With the nozzle at 51 °C, the hotend fan spins and the alert disappears.

   If that does not fix it: Replace the fan (next step).

4. Replace the fan

   If you have a spare fan, or a complete hotend with fan, fit it; the hotend fan must face the right way. On the X1 and P1 the part cooling fan is built into the front cover and the whole cover is replaced; on the H2 series the fan is replaced on its own.

   Check: The fan spins without odd noises and the alert does not return.

   If that does not fix it: If nothing fixes it, the TH board and extruder connection board need replacing: contact Bambu Lab support.

5. On the A1 and A1 mini

   Set the hotend to 0 °C, check with a pen that the hotend fan blades turn, switch the printer off and reconnect the hotend fan cable; then power on and heat to 51 °C.

   Check: The hotend fan spins once it passes 50 °C and the alert disappears.

   If that does not fix it: Replace the hotend fan and, as a last resort, the TH board, or contact Bambu Lab support.

Prevention

• Check the fans weekly and clean them with compressed air with the printer off, holding the blades so they do not spin.
• Wait for the toolhead to cool before touching it.
• When replacing a fan, note its orientation before removing the old one.

Still not fixed?

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Printers it applies to

Bambu Lab X1 Carbon, X1, X1E, P1S, P1P, P2S, H2D, H2D Pro, H2S, A1 and A1 mini.

Official sources

This guide summarises the official documentation linked here:

• HMS_0300-0300-0002-0002: The speed of hotend fan is slow. · Bambu Lab
• HMS_0300-0400-0002-0001: The Part Cooling Fan speed is too slow or stopped. It may be stuck, or the connector may not be plugged in properly. · Bambu Lab
• Bambu Lab X1 Maintenance Recommendation · Bambu Lab
• A1 Maintenance Guidelines · Bambu Lab