The dreaded F dl error code

Believe I have searched every forum with no success.

Done the remove power, power up after 1 and 24 hours.
Have replaced the door latch, the error code.
Replaced the CCU unit, error code.
Cleaned all the connectors with CRC QD Electronic Cleaner, the error code.
Diagnostics will only run to the first step: C:00 Door Lock

At a loss for anything else to check on this machine

Any suggestions, except picking it up ~ 2" and dropping it - I did see this somewhere, would be massively appreciated

Thanks,
rpcole