The meaning of B1421 Code is required to identify for resolving the difficult of the engine. The body part of the engine seems the main problem and for solving this problem, you do not need to change any component. You need to read the manual as well as know the model and manufacturer. However, you can easily solve the problem by the professional and do not try to solve the problem by yourself if you do not have all necessary component or tools. About the B1421 code, it would be worthy to inspect cautiously the wire harness close the intake various bracket.