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Siemens SINUMERIK Controller
Program/G-code · Intermediate · 30-120 minutes
Siemens 840D 16939 - Channel action <ALNX> rejected due to active gear change
Siemens SINUMERIK 840D alarm 16939: Channel action <ALNX> rejected due to active gear change. This alarm indicates a program or channel-level error on the SINUMERIK control. The part program or machine function cannot be executed as commanded.
16939
Siemens 840D 16939 - Channel action <ALNX> rejected due to active gear change
Channel action <ALNX> rejected due to active gear change
Siemens SINUMERIK 840D alarm 16939: Channel action <ALNX> rejected due to active gear change. This alarm indicates a program or channel-level error on the SINUMERIK control. The part program or machine function cannot be executed as commanded.
Safety
- Refer to Siemens documentation
- Ensure qualified technician performs repairs
Common Causes
- Part program contains an illegal or unsupported command for the current machine configuration
- Channel or axis configuration does not support the programmed function
- Required machine option not enabled for the commanded function
- Axis assignment or transformation configuration error
- Program execution sequence error
Troubleshooting Steps
- 1Identify the program block that triggered the alarm — note the channel and block number.
- 2Review the commanded function against the SINUMERIK programming manual.
- 3Check if the required machine option is enabled for this function.
- 4Verify axis assignments and transformation settings are correct for the application.
- 5Consult the Siemens SINUMERIK alarm manual for alarm 16939 specific remedy.
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Always verify with your machine manual or a certified technician before performing service procedures.