Unfortunately custom fault codes list would not help here as RealDash does not find any error codes.
To troubleshoot this, your would need to enable debug logging:
How to send a debug log - General / Frequently Asked Questions - RealDash Forum
Then use the Quick Settings ‘Read Error Codes’ option and upload the debug log from the settings.
In addition we would need to know what is the expected result (the error code) that should come up when errors are read.