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Check DIAGNOSIS screen > #300-#307 (DGN for I/O status) to verify which axis limit switch is active. Look for OT- signal for the indicated axis n showing '1' status, confirming hardware switch activation.

Check POSITION screen (ABSOLUTE, MACHINE coordinates) to determine exact axis position. Compare against parameter #1320-#1327 (stored stroke limit negative) to verify axis is beyond expected travel range.

If machine has absolute encoder (serial or Ai), place mode selector to JOG and carefully jog axis in positive direction away from limit switch. Monitor DIAGNOSIS screen to confirm OT- signal turns off as axis clears the switch.

Proceed slowly with manual feed override reduced to 10-25%. Ensure no mechanical obstructions exist before jogging.

After clearing hardware limit, execute reference position return (zero return) for the affected axis to re-establish machine coordinates. Verify reference position parameter #1815 (reference position return check) = 0 or 1, then verify stored stroke check parameters #1320-#1327 are correctly set to prevent recurrence.

Visually inspect the negative hardware limit switch and actuating dog/cam on the affected axis. Verify switch mounting bracket is secure and switch has not shifted from original position. Check for physical damage or debris blocking switch.

Perform inspection with machine power OFF and axis mechanically locked out per LOTO procedures.

Check DIAGNOSIS screen > #300-#307 I/O status while manually (hand wheel or MPG) moving axis near limit position. Verify OT- signal transitions cleanly at expected position and corresponds to parameter #1320-#1327 stored stroke limit setting.

If switch position is incorrect, mechanically adjust limit switch or dog/cam position to provide adequate overtravel margin beyond normal programmed working envelope. Ensure minimum 5-10mm clearance from maximum programmed travel to hardware limit activation.

Adjustment requires mechanical access. Follow machine builder specifications for proper limit switch positioning and adjustment procedures.

After adjustment, verify stored stroke limit parameters #1320-#1327 (negative limit) and #1321-#1328 (positive limit) match actual hardware switch positions. Set parameter #1320 (axis n negative) to position approximately 2-5mm before hardware switch activation point.

With axis positioned well within normal travel range, check DIAGNOSIS screen > #300-#307 to verify OT- signal status is '0' (inactive). If signal shows '1' when switch is not mechanically activated, confirms electrical fault.

Check limit switch wiring at switch terminals, machine I/O terminal block, and CNC I/O module (JD1A/JD1B connector). Verify 24VDC supply voltage present and return signal continuity. Check for damaged cables, loose connections, or moisture ingress causing short circuits.

Use multimeter to verify 24VDC I/O signals. Do not bridge or jumper limit switches to bypass alarm without proper authorization and risk assessment.

Temporarily swap or disconnect the suspect OT- switch and monitor DIAGNOSIS screen #300-#307 signal status. If signal remains active with switch disconnected, fault is in wiring or I/O card input circuit. Check PMC ladder (I/O LINK screen) for input address assignment and signal routing.

Bypassing hardware overtravel protection removes critical safety function. Only perform for diagnostic purposes with machine safeguarded and under controlled conditions.