The error engine P0821 Code is helping content what you need to use for solving the car engine. The meaning of the code is found from the car manufacturer and if you know the name of the car and manufacturer, read the engine manual. Do not try to solve the car engine without getting any information of the car engine. Do not try to solve the car engine by yourself. You must allow automobile engineer to fix the car engine. The real meaning of the code gives real information only and the automobile engineer knows the process of solving the car engine and find the real meaning of the code.