Error message

HMS_0300_0300_0002_0002 The speed of hotend fan is slow
” The speed of the hotend fan is slow. It may be stuck and need cleaning. “

What it is

There is a speed feedback signal from the hotend fan. The hotend fan (or called heatbreak fan) is used to keep the filament outside the nozzle cool and solidify. If the hotend fan speed keeps low, then the hotend heatsink temperature will rise and cause the filament to soft and then jam inside the heatbreak.

Below are the possible reasons:

  1. The fan blade is stuck by something ( like filament ) and cannot spin freely
  2. Poor contact between the hot end fan and the TH mainboard connection
  3. The fan is faulty
  4. The TH board is faulty

Safety warning and Machine state before starting operation

When cleaning the fan, the fan may start spinning suddenly and cause injury. But as there is no switch that can turn on/off the hotend fan, using a pen or screwdriver to do the following steps is recommended.

Troubleshooting guide

Step 1

Set the hot end temperature to 0 °C. When the hot end temperature drops below 50°C, the hot end fan will automatically shut down (the fan turns on automatically when the hot end reaches 50°C and turns off automatically when it falls below 50°C).

Step 2

Take off the front cover, and use a pen or a screwdriver to spin the fan blade, to see if the fan blade was stuck by something. If yes, please remove it.

Step 3

After cleaning up the mess, reconnect the 4-PIN connector on the hot end fan. Set the hot end temperature to 51°C. The hot end fan will start running again (if it is not stuck or broken) and see if this HMS message disappears.

If have a P1P printer, please be careful not to plug the hot end fan in the wrong way.

Correct installation

Step 4 

If you have a spare hot end fan or a complete hot end assembly (with the fan), you can replace it with a new fan to see if it can fix the problem.

Step 5

If you still can’t solve this problem. It is recommended that you re-plug the 10-pin connector. And check whether there is any sign of damage on the 10-pin plug.

If the error still exists after re-plugging the two connectors multiple times, please take photos of the plug of the 10-pin connector and the hot end fan, upload log files, and contact the customer support team.

If your X1 series printer has a V9 TH board, please replug both ends of this FPC. (Because the BTB socket is small, the installation of the FPC is a bit tricky. It is recommended that you only plug and unplug one end at a time and do not press too hard.)

X1 series  V9 TH board

Replacing the toolhead TH board assembly (V8)| Bambu Lab Wiki

Replace the toolhead boards (V9) | Bambu Lab Wiki

If your printer model is P1P, please replug both ends of this FPC.

TH board of P1P printer

PCBs on the toolhead of P1P | Bambu Lab Wiki

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