Brother MFC-P2500 User Manual page 57

What do the LED indications mean
This section refers to the following LEDs on the printer control panel.
Alarm LED
The Alarm LED indicates a printer error status.
When the Alarm LED is on and the printer has detected and error condition,
refer to
4 and clear the problem and make the printer ready to print.
Data LED
LED
When the toner cartridge is empty,
referring to Chapter 3.
LED
On 
the 'Error Messages that Appear on the LCD Panel' section in Chapter
LED

On
Blinking
LED

On
Blinking
1-48
Status
The printer has detected an error.
Status
Print data remains in memory.
The printer is receiving data from the
computer.
Status
The toner cartridge is empty.
The toner cartridge is nearly empty.
replace the toner cartridge with a new one