If you have multiple identical axes, you can swap the cables or drives. If the alarm stays on the Z-axis, the problem is the motor or cable; if it follows the drive, the amplifier is the culprit.
The discrepancy between the command pulse and the position feedback pulse (from the encoder) has exceeded the allowable limit (set by parameter 1828). In simple terms: the CNC told the Z-axis to move, but the feedback says it didn't move properly (or at all). fanuc 414 servo alarm z axis detect error