Brother HL-5130 - Toner Empty message; Replacing the toner cartridge

HL-5130/5140/5150D/5170DN SERVICE MANUAL
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2.3.3 Cassette sensor / Paper empty sensor (HL-5140/5150D/5170DN)
Detect if the paper tray is installed. They also detect if there is paper in the paper tray.
Fig. 3-38
2.3.4 Paper eject sensor
Detects if paper is ejected from the fixing unit.
Fig. 3-39
Paper empty sensor
Eject sensor PCB ASSY
Fixing unit
Cassette sensor PCB ASSY
Cassette sensor