Can you tell me what the fault code B10D7 means on a Ford Transit?

If your Ford Transit shows fault code B10D7, it means there is an issue with the key programming for the passive anti-theft system (PATS) or a problem with the body control module (BCM). This could result in your Transit being immobilized, as the system may not recognize the key as compatible. Typically, the BCM reads the key in the ignition key cylinder during programming, and if it's a valid PATS key, it saves it in memory. The B10D7 code points to a failure in this process, which could be triggered by a long period of battery disconnection or a dead battery. A blown fuse can also cause this error, so check those first, possibly fuse 20 which is shared with ABS. Ensure all cables are good and connections are secure. If those are not the issue, inspect the sensors near the key barrel (such as the antenna at the switch) after confirming the key itself is not the problem.