If the TIA Portal or STEP 7 project has a module configured (e.g., 16-channel DI) but a physically different module (e.g., 8-channel DI) is plugged in, the CPU will generate Fault 0A7991 during startup or I/O update.
When the drive outputs torque > p2175 but speed remains < 5% of setpoint for longer than p2177 or p2178, the system triggers 0A7991. siemens fault 0a7991
Instead of waiting for F07991, configure warning A07991 with a lower threshold: If the TIA Portal or STEP 7 project
| Step | Action | |------|--------| | 1 | Clear mechanical obstruction. | | 2 | Increase torque limit (temporarily for testing). | | 3 | Check brake control logic & power supply. | | 4 | Perform encoder test (p2500, p2504). | | 5 | Recalculate motor parameters (p304, p305, p311). | | 6 | Disable "stall detection" temporarily (p2178) for diagnosis only. | Instead of waiting for F07991, configure warning A07991
Note: Do not disable stall protection permanently unless advised by Siemens support.
Before diving into the causes, it is important to recognize how this fault manifests in a live production environment:
Insufficient power to a remote I/O station (e.g., ET 200M) can cause modules to power cycle, leading to startup errors that manifest as 0A7991.