This engine P1721 Code lets you know about the problem of the car engine and engine area. You need to know the meaning of the code when you get the code. Meaning of the code should be taken from the car manufacturer. If your car manufacturer does not provide correct meaning of the code, you cannot fix the car engine easily and then you have to depend on the automobile dictionary meaning of the code for solving the car engine. The problem of the car engine is powertrain and the powertrain is not difficult to solve. You do not need to change or add any more component for solving the car engine.