The diagnosis P255D Code comes at the diagnosis time and this code is a supporting code for the automobile engineer to solve the car engine problem. Do not allow any meaning of the code for solving the car engine. There are several meanings but the automobile engineer needs to find the meaning of the code what is from your car manufacturer. You should not take any step for solving the car engine if you do not know how to solve the car engine problem. You may face new problem in the car engine if you follow wrong step for solving the car engine.