Fault 0a7991 Best - Siemens

This one habit prevents 80% of 0A7991 occurrences.

| Symptom | Solution | | :--- | :--- | | Fault 0A7991 appears | Check p0840 (ON/OFF1) = 1 | | Fault occurs during p1910 | Ensure no active OFF2/STO | | Fault occurs after reset | Perform p0970 factory reset | | Fault remains after all checks | Measure 24V DC on control terminals | siemens fault 0a7991 best