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Access Siemens HMI > Diagnostics > Machine Data > Search for MD $MA_SAFE_POS_LIMIT_PLUS and MD $MA_SAFE_POS_LIMIT_MINUS for the affected axis (e.g., $MA_SAFE_POS_LIMIT_PLUS[AX1]).

Cross-reference the current parameter values against machine documentation and physical axis limits. Verify that PLUS limit is less than the maximum positive travel and MINUS limit is greater than the maximum negative travel in machine units.

Ensure safety boundaries do not conflict with valid working envelope.

If parameters are incorrect, modify them via HMI or Siemens SINUMERIK Operate interface. After adjustment, perform a power cycle (warm restart) to reload machine data into NCK memory.

Execute a reference run (machine zero offset) using MD $MA_HOME_SWITCH_TYPE and verify axis returns to valid position within the new safe limits.

In Siemens HMI Diagnostics > Actual Values, monitor the position actual value (VAL) for the affected axis during manual jog. Compare NCK position display against a dial indicator or external measurement device to confirm position discrepancy.

Do not exceed safe limits during testing; stop immediately if alarm recurs.

Check MD $MA_REFPOINT_POS (reference point position) and verify the axis was properly referenced after power-up. If reference offset is incorrect, re-execute homing cycle using G74 or machine reference point button.

Inspect encoder connectors (X-axis, Y-axis, Z-axis feedback cables on drive terminal) for corrosion, loose contacts, or damage. On SINUMERIK 840D, verify resolver or encoder signal in Diagnostics > Drive > Actual Values > Feedback Voltage.

If position error persists, perform an axis compensation run or recalibration using Siemens commissioning tools. If encoder failure is suspected, replace encoder and re-reference machine zero.

Immediately stop all machine motion and check for physical obstructions, broken mechanical stops, or deformed limit switch brackets on the affected axis. Visually inspect end-of-travel mechanical hard stops.

Do not attempt to move the axis if mechanical damage is suspected; risk of further equipment damage.

In HMI Diagnostics > Drives > Servo Control, verify servo loop gain (MD $MA_SERV_CNTRL_GAIN) and position loop closed-loop error (MD $MA_POS_ERR_LIMIT). High position lag or servo faults indicate loss of axis control authority.

Check for active axis velocity limit overrides (MD $MA_MAX_AXI_SPEED) and verify soft limit enable status (MD $MA_LIMT_AXI_SWITCH_ON = 1). Confirm backlash compensation MD $MA_BACKLASH is properly configured for the axis ballscrew.

If mechanical stops are intact and servo is responsive, manually jog the axis away from the overtravel limit, then re-execute reference cycle. If alarm persists, contact Siemens field service for servo calibration and mechanical inspection.