27004

Check physical mode selector switch

Inspect the mode selector switch on machine control panel for mechanical binding, debris, or physical damage preventing return to neutral position.

Ensure machine is in safe state before manipulating mode switches

Verify switch contact operation

Use multimeter to check continuity across handwheel mode switch contacts while cycling switch positions to identify internal contact failure.

Check switch wiring diagram in electrical documentation for correct contact assignments

Monitor PLC input status

Navigate to Diagnostics > PLC > Inputs/Outputs and monitor the handwheel mode request input signal while operating the selector switch to confirm signal changes.

Replace faulty switch if confirmed

If switch contacts are faulty or mechanically damaged, replace the mode selector switch with identical Siemens-approved component per machine documentation.

Access PLC program online

Connect to PLC via STEP 7 or TIA Portal and go online with the PLC program to monitor mode group control logic execution.

Look for FB or FC blocks named MODE_CTRL, MODE_SEL, or similar in the program structure

Monitor mode group DB11 interface

Open DB11 (NCK interface) and monitor DBX0.3 (handwheel mode request) and related mode request bits to identify which signal remains active.

Do not modify DB11 values directly as this can cause NCK communication errors

Trace mode control logic

Use PLC program status to trace the mode control logic and identify latching conditions, interlocks, or timer functions preventing handwheel mode reset.

Reset latched conditions

Clear any latched mode conditions through HMI reset functions or by temporarily forcing the problematic logic elements to reset the handwheel request.

Check handwheel unit connections

Inspect all connections to the electronic handwheel unit including power supply, encoder signals, and enable/mode request lines for loose connections or damage.

Handwheel units typically connect via 15-pin D-sub or similar multi-pin connector

Verify handwheel enable signal

Navigate to Diagnostics > NCK > Handwheel and check the handwheel enable status and encoder signal quality indicators.

Disconnect handwheel unit power before checking connections to prevent damage

Test with handwheel disconnected

Temporarily disconnect the handwheel unit and attempt to clear alarm 27004 to isolate whether the fault is in the handwheel hardware or system logic.

Replace handwheel unit if faulty

If alarm clears with handwheel disconnected, replace the electronic handwheel unit with identical Siemens part number and reconfigure handwheel parameters if necessary.

Access NCK machine data

Navigate to Commissioning > Machine Data > Channel and locate mode group parameters MD11210 (MODE_GROUP_CHANGE_ENABLE) through MD11240 series.

Backup machine data before making any parameter changes

Verify mode group configuration

Check MD11210 is set to 1 to enable mode group changes and verify MD11220 (MODE_GROUP_MASK) includes handwheel mode bit if handwheel operation is required.

Review handwheel-specific parameters

Check handwheel configuration parameters MD30200-MD30240 series for proper axis assignment and enable settings that may affect mode group operation.

Reset and test mode transitions

After parameter corrections, perform NCK reset (Power On Reset) and test mode transitions between JOG, AUTO, and handwheel modes to verify proper operation.