SV0405 Reference Return Fault (Grid Search) fault in Fanuc drive

SV0405 Reference Return Fault (Grid Search) fault in Fanuc drive

Description

SV0405 occurs during the "Zero Return" or "Homing" sequence on machines equipped with physical limit switches (dogs). When you command a Reference Return, the axis moves to the deceleration switch, slows down, and then searches for the "Grid Zero" pulse on the encoder. SV0405 triggers if the Reference Return sequence was initiated but failed to complete correctly. The machine is effectively saying, "I tried to find Home, but the signals didn't make sense."

Cause

• Switch Failure: The deceleration dog switch stuck closed, or opened too late.
• One-Rev Signal Missing: The encoder failed to output the Z-pulse (marker pulse) required to establish the precise home point.
• Speed Too High: The "Reference Counter" capacity was exceeded because the axis didn't slow down fast enough after hitting the switch.
• Start Position: Attempting to home the machine when it is already sitting *on top* of the limit switch.

Solution

1. Move Axis: Jog the axis to the center of travel (away from the switches) and try again.
2. Check Decel Switch: Go to the Diagnostic screen (X-bit status). Press the physical switch on the rail. Does the bit flip from 0 to 1? If not, the switch is bad.
3. Clean Switch: Often, chips get packed around the plunger, preventing it from springing back.
4. Grid Shift: If the motor was replaced, the Grid Shift parameter might need adjusting to align the electrical zero with the mechanical switch position.