Unable to clear P1927-62 on Ford Focus Mk2 1.6 TDCI

I have a 2005 Ford Focus Mk2 1.6 TDCI showing a P1927-62 error code from the PCM that I can't get rid off.

It seems I can clear the error with FORScan, but it comes right back. I have tried changing the Fuel Additive Tank (FAT) as well as the Fuel Additive Control Module (FACM), but this doesn't make any difference. As part of changing the FAT, I have also run the service procedures for priming and refilling the FAT, but this doesn't make any difference. I have also tried resetting the PCM.

I don't understand what could be causing this error even with another FAT and another FACM. It also puzzles me that the error code is in the PCM, not the FACM. Could something be wrong in the PCM?

Any ideas or advice would be appreciated.
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