The B1243 Code has a number of meanings and to get the exact meaning of the code, it is needed to recognize the model and manufacturer of the engine. It is necessary to know the meaning and reading manual is a good way to understand the meaning. Deactivation of cylinders is realized by freeing a synchronizer pin that usually interlocks the cam rocker arms and follower. B1243 code resolves the synchronizer pin is released using hydraulic pressure which is organized by a dedicated solenoid. The catalytic converter has an oxygen sensor in behind and in front it. When the vehicle is hot and running in locked loop mode, the upstream oxygen sensor waveform reading should vary.