The F01003 error code in your Siemens Sinamics G120 drive indicates an acknowledgement delay when accessing memory. This means the drive tried to read or write data from its memory, but the memory unit didn't respond within the expected time.

Here are some possible causes of the F01003 error:

• Memory hardware issue: There could be a problem with the G120's internal memory itself, such as a faulty memory chip.
• Communication error: The communication link between the control unit (CU) and the memory unit might be malfunctioning.
• Software glitch: A temporary software issue within the drive could be causing the delay.

Here's how you can troubleshoot the F01003 error:

1. Power cycle: A simple power reset can sometimes resolve temporary glitches. Completely turn off the drive and all connected equipment, wait for a few seconds, and then power everything back on.
2. Check connections: Ensure all cables connecting the memory unit to the CU are properly secured and not damaged.
3. Clear fault memory: The drive might store additional information about the error.