Siemens Fault 0a7991 Now

In pumping applications (vertical turbine pumps, centrifugal pumps), 0A7991 often points to vapor lock or cavitation. The drive attempts to spin the impeller, but gas bubbles in the fluid compress rather than transfer torque. The motor sees no load (low torque, zero speed) – triggering the fault.

A: If the PLC has OB 122 and remains in RUN, you may be able to clear the fault by correcting the external wiring or replacing the module online. If the CPU is in STOP, you must perform a memory reset or power cycle after fixing the cause. siemens fault 0a7991

Scenario: A food processing plant using a SINAMICS G120 to drive a dough mixer reports recurring fault 0A7991 every morning at first start, but runs fine rest of the day. Solution :

Investigation:

Solution:

Result: Fault 0A7991 eliminated.

If the fault is intermittent: