The B1391 Code is an error code of an engine and this code is difficult to describe till you know the name of the model and manufacturer. The code may have different meanings. The key multi-displacement scheme is turned off contradictory pairs of cylinders, letting the engine to have 3 diverse settings and movements. The B1391 code had an extravagant diagnostics way, with showing engine worry codes on the air training show. However, the method was worrying, mistaken by customers, and a rash of random failures led to the expertise being rapidly discharged. You should take a test drive to understand well of the engine problem solved or not.