The meaning of the car engine code is necessary to know and you will get the real meaning of the engine C1234 Code from online. The general meaning is automobile meaning what is not helpful for solving the problem. The catalytic converter has an oxygen sensor what is set in front and behind it. When the automobile is deep and running in shut loop mode, the upstream oxygen sensor waveform reading should alter. The engine C1234 code solves the synchronizer pin is unconfined using hydraulic pressure which is maintained by a dedicated solenoid. Taking the car for test is necessary.