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Access PLC diagnostics and monitor DB19.DBX0.0-0.5 (mode selection bits) to verify only one mode is requested at a time. Check for simultaneous active mode signals.

Review PLC program logic (OB1/FC/FB blocks) controlling mode switching to ensure proper interlocking exists between AUTO, MDA, and JOG mode requests with sufficient delay times (minimum 100ms between mode changes).

Verify mode enable acknowledgment signals in DB21 are being properly reset before initiating a new mode request. Check DB21.DBX0.0-0.5 acknowledgment bits match DB19 requests.

Test mode switching manually from HMI in both directions (AUTO to JOG and JOG to AUTO) while monitoring PLC signal timing with online diagnostics to identify sequence violations.

Ensure machine is in a safe state with no axes moving during mode switching tests.

Check NCK load (CPU utilization) in diagnostics menu under 'System Data > NCK'. If NCK load exceeds 80%, investigate cycle time issues or optimize part program to reduce processing demand.

Verify communication between HMI and NCK by checking 'Diagnostics > Communication' for timeout errors or buffer overflows. Look for alarms in 10xxxx or 60xxxx range indicating communication problems.

Perform a cold restart of NCK (power cycle) to clear communication buffers. Navigate to 'Startup > Control Boot' and execute controlled shutdown followed by power cycle.

Save all current settings and active programs before performing NCK restart. Coordinate with production as this will interrupt all operations.

Check system data for parameter corruption by backing up and comparing MD settings with known good configuration. Review MD11210 (PLC interface mode) and MD11200 (basic interface configuration) for correct values.

Verify current user login level has sufficient authorization for mode switching. Log in with manufacturer or service level (password level 3 or higher) and attempt mode change again.

Check MD11210 $MN_PLC_BASIC_PROG_FUNCTION_MASK bits 0-2 to ensure mode switching via PLC interface is enabled. Bit value should allow both continuous and JOG mode activation.

Changing MD11210 requires NCK reset. Document original value before modification.

Review safety integrated configuration (MD36600-36610 series) if Safety Integrated is active. Verify that no safety-related mode restrictions are blocking JOG or continuous mode operation.

If alarm persists, perform system software consistency check via 'Startup > System Data > Consistency Check' and review commissioning files for corrupted archives or incomplete software installation.

System consistency check may take 5-10 minutes and temporarily disrupt operations.