• Code: U4-1
• Description: Fuser On Time fail
• Causes: -During the Warm-Up period, the Control Thermistor does not detect the Ready temperature even when the specified time is passed after the Main Lamp is ON. -During the Standby period, the Control Thermistor does not detect the specified temperature even when the specified time is passed after the Main Lamp is ON. -During the Standby period, the Control Thermistor does not detect the specified temperature even when the specified time is passed after the Sub Lamp is ON. - During idling after power-on, the Control Thermistor does not detect the idling stop temperature even after the specified time is passed. -During print, the Control Thermistor does not detect the specified temperature even when the specified time is passed after the Main Lamp is ON. -During print, the Control Thermistor does not detect the specified temperature even when the specified time is passed after the Sub Lamp is ON.

• Code: U4-2
• Description: Over Heat Temp fail
• Causes: - The Control Thermistor detects a temperature higher than the specified value. - The Lamp Change Thermistor detects a temperature higher than the specified value.

• Code: U4-3
• Description: Center STS fail
• Causes: The Center STS broke.

• Code: U4-4
• Description: REAR STS fail
• Causes: The REAR STS broke.

• Code: U4-5
• Description: P/R STS fail
• Causes: The P/R STS broke

• Code: U4-7
• Description: Cold-Sagging recovery fail
• Causes: The Center STS/FS1 detects that it does not recover from Cold-Sagging after the specified time is passed.

• Code: U4-8
• Description: Hot-Sagging recovery fail
• Causes: The Center STS/FS1 detects that it does not recover from Hot-Sagging after the specified time is passed.

• Code: U4-9
• Description: Fuser Fan fail
• Causes: The Fuser Fan broke.