SV0406 Reference Position Return Error fault in Fanuc drive

SV0406 Reference Position Return Error fault in Fanuc drive

Description

SV0406 differs from SV0405. While SV0405 means "I failed to find the reference," SV0406 means "I found the reference mark, but it wasn't where I expected it to be." During the Homing cycle, the machine hits the deceleration dog, slows down, and looks for the grid pulse. If the distance traveled between the dog switch and the grid pulse varies significantly from the previous setting, the CNC flags this as a reliability risk. It thinks the switch moved or the motor skipped a pole.

Cause

• Dirty Switch: The deceleration dog switch is sticky. It released late, changing the distance calculation.
• Grid Mask: The switch is placed too close to the encoder's Z-pulse. This is the "One Revolution" issue. If the switch releases exactly on top of the Z-pulse, the system might pick the next pulse, shifting the home by one screw pitch.
• Belt Slip: Mechanical slippage caused the physical relationship between the switch and motor to change.

Solution

1. Shift Dog: Physically move the deceleration cam/dog slightly (2-4mm) along the rail to change the timing of the switch release relative to the motor rotation.
2. Check Parameter 1850: This parameter (Grid Shift) might be set incorrectly, putting the electrical grid right on the edge of the switch release point.
3. Clean Switch: Ensure the plunger moves instantly.