Both errors are signalling a temperature problem in fuser assembly.
The solution below applies to several Brother models. Depending on the model, the reset procedure may be different.
Brother Error 6A means that the thermistor located in the fuser assembly did not detect that required temperature had been reached in valid time.
First you can try entering in maintenancemode and clearing the error. If that does not work, that means that the thermistor, the lamp, or the whole fuser assembly must be replaced.
Error 6E is similar. 6E is diplayed when thermistor detect that the fuser temperature is not going up at least at 2°C every for 5 seconds.
As for 6A, first reset the code. If the error does not clear the fault can concern the thermistor, the fuser lamp or the power supply to the fuser assembly.
To reset the error code follows these steps:
1. Press MENU *,2,8,6,4 . Press keys within 2 seconds.
2. The machine beeps and display shows “maintenance".
3. Look for Init or Reset on menu, and enter the corresponding parameter.
4. To exit press 99.
This procedure above usually works on MFC-8xxx model. On other models you may need to do the following:
1) Unplug machine.
2) Hold down menu key. Plug in machine.
3) Release menu key.
4) Enter 91
5) Enter 99
1) Disconnect the printer power cord.
2) Hold down the menu key while plugging in machine at same time.
3) Enter 99 while holding down menu key
4) After menu says " wait" push the stop/exit button to get out of the maintenance mode.
If that does not work, it means that the fuser assembly must be replaced. Here the part for MFC-8440: Genuine Brother Mfc8440 Fuser Assembly.