Lee is on the money, if you had a boost pressure fault code hopefully one of the first things to check would be the accuracy of the boost pressure sensor and if good working off the data outputted thereafter.

The rail pressure sensor should be no different, you have an issue with the reading so the first thing to do is prove what you are being told via the scan tool is true.

After that you can rely on the data that is being send to you via the diagnostic tool.

Regards
Mark