This P0731 Code is found in the car engine and you need to study the real meaning for solving the car engine. The engine code comes by the testing the car engine. You will get false meanings of the same engine code but do not allow any meaning of the code for solving the car engine. Real meaning of the engine code is very helpful for solving the car engine problem. Read the manual of the car engine and find the real meaning of the code by the name of the car and manufacturer. Once the car engine is ok, you need to take it for a test drive.