Brother DCP-L8400CDN Service Manual page 450

1.3.34 Display of device error codes (Function code 82)
<Function>
This function is used to display the latest error code on the LCD.
<Operating procedure>
(1) Press the 8 and 2 keys in this order in the initial state of the maintenance mode.
"MACHINE ERR XXXX" is displayed on the LCD.
(2) Press the X key to return the machine to the initial state of the maintenance mode.
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