OBD-II code family
Software Incompatibility With Battery Energy Control Module (U0312–U034C)
3 codes describing the same fault on 3 enumerated slots. The letter is the index your manufacturer assigned — it is not a physical difference, and it does not carry across makes.
What these codes mean
These codes describe one fault across several enumerated slots. The letter — A through C — is the index the vehicle manufacturer assigned to that energy control module, and it carries no meaning that transfers between makes. There is no industry-standard table mapping letters to physical positions, so the wiring diagram for your exact year, make and model is the only authority on which component your code refers to.
Because the letter is an index rather than a physical distinction, the diagnosis is the same for every member of this family. What changes between them is only which unit you are looking at once you have identified it from the service data.
A note on what the letter implies about your vehicle: low letters are fitted almost universally, while high letters only exist on vehicles that carry many of these components. If a code with a high letter appears on a vehicle unlikely to have that many, the code has most likely been misread or reassigned by the manufacturer — check it against your make before spending anything.
Which energy control module is mine?
There is no generic answer, and any source that gives you one is guessing. The letter is assigned by the vehicle manufacturer, and the same letter refers to different physical components on different makes — sometimes on different model years of the same vehicle. The only authoritative source is the wiring diagram or service information for your exact year, make, model and body style.
A manufacturer-specific definition always outranks the generic one. If your make publishes its own meaning for this code, use that and ignore the generic description.