Siemens Fault 0a7991 New! Link

Fault Report: Siemens Fault 0A7991

Disable the Identification ManuallyIf you do not wish to run the identification (e.g., during bench testing or Factory Acceptance Tests (FAT)), change these parameters: siemens fault 0a7991

• In TIA Portal, add Organization Block OB 122 to your program.
• Leave it empty or add minimal error handling logic.
• Download to CPU. The PLC will now remain in RUN even if the fault recurs, allowing for safe shutdown.

If you do not wish to perform the identification (e.g., during bench testing without a motor), you can disable it via the Siemens Parameter List: In TIA Portal, add Organization Block OB 122

If the alarm does not disappear or prevents the drive from running, use the following methods to resolve it: 1. Complete the Identification Routine If you do not wish to perform the identification (e

• Mechanical check: Shaft rotates freely when cold.
• Parameter check: Motor data correct.
• Live data: On cold start, torque peaks to 180% but speed sticks at 0 RPM for 3 seconds, then fault trips.
• Root cause: The dough hardens overnight. The standard torque limit (p1520 = 150%) and detection time (p2177 = 2s) are insufficient to break the cold dough.

9. Collect info before contacting support

Prepare:

• PLC in STOP or intermittent STOP: The CPU may transition from RUN to STOP mode if the OB 122 (I/O access error organization block) is not programmed. If OB 122 exists, the PLC may stay in RUN, but the affected I/O channel will show invalid data.
• SF (System Fault) LED Blinking/Steady: The red SF LED on the CPU and on the affected I/O module will illuminate.
• BF (Bus Fault) LED Activity: If the fault is related to PROFIBUS/PROFINET communication, the BF LED will flash, indicating a bus-related issue.
• Inconsistent Process Values: Sensors or actuators connected to the affected channel may produce erratic readings, defaults (e.g., 0 or 7FFF), or fail to respond.
• TIA Portal Online Diagnostics: When going online in TIA Portal, the diagnostic buffer will show entry "0A7991" with a timestamp, often accompanied by additional details like "Module is faulty or not available."

Manual Override (Disable):If you cannot run the identification (e.g., during a Factory Acceptance Test without a motor), you can force the alarm to clear by manually changing settings: Set p1900 = 0 (Inhibits Motor ID). Set p1300 = 0 (Switches to V/f standard control mode).