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Siemens SINUMERIK Controller
Servo/Axis · Intermediate · 10-20 minutes
Siemens 840D 16903 - Channel program control: action <ALNX> not allowed in the
The relevant action cannot be processed now. This can occur, for instance, during read-in of machine data.
16903
Siemens 840D 16903 - Channel program control: action <ALNX> not allowed in the
Channel program control: action <ALNX> not allowed in the
The relevant action cannot be processed now. This can occur, for instance, during read-in of machine data.
Safety
- Refer to Siemens documentation
- Ensure qualified technician performs repairs
Common Causes
- Machine data (MD) is being read or written while the action is being attempted
- Control system is in startup or initialization phase when command was issued
- Program execution attempted during active parameter modification or system configuration
- Action conflicts with current machine state or operating mode
- Synchronization issue between NC kernel and action queue processing
Troubleshooting Steps
- 1Wait for machine data read/write cycle to complete before issuing the action command again
- 2Check if control system is still initializing; allow full startup sequence to finish before resuming program execution
- 3Verify the machine is in a stable operating state (not in diagnostics, setup, or configuration mode)
- 4Review the specific action %2 being attempted and confirm it is appropriate for the current channel %1 state
- 5If issue persists, perform a controlled system restart (Power Cycle or warm restart) and retry the operation from a safe point in the program
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Always verify with your machine manual or a certified technician before performing service procedures.