Internal Error

What does 8491 mean?

An unspecified internal error has been detected within the Safety PLC, indicating a potential hardware or firmware defect that impacts core functionality. This type of error can lead to unpredictable behavior and compromise the safety integrity level of the system. Prompt resolution is required to prevent hazardous conditions.

• Unrecoverable hardware fault (e.g., processor, memory, internal communication bus) within the safety PLC.
• Corrupted system software or firmware preventing fundamental operation.
• Transient electrical disturbance or power anomaly affecting critical internal circuits.
• Over-temperature condition causing component instability or failure.
• Wear and tear of components over time, leading to intermittent or permanent failure.

Click steps to track your progress.

1. 1

   Access the safety PLC's diagnostic buffer (e.g., via TIA Portal online diagnostics) for any specific sub-error codes or additional information.

2. 2

   Perform a hard power cycle of the safety PLC by completely removing and reapplying the 24VDC supply voltage at terminals L+ and M.

3. 3

   Check the stability and voltage level of the 24VDC power supply to the safety PLC, using a multimeter or oscilloscope.

4. 4

   Ensure the operating temperature within the control cabinet and around the safety PLC is within the manufacturer's specified range (e.g., -20°C to +60°C).

5. 5

   Attempt a full memory reset (e.g., "MRES") on the safety PLC, followed by a complete re-download of the safety project and, if applicable, firmware.

6. 6

   If the internal error persists after these steps, replace the safety PLC CPU module with a new, identical spare.