The car engine may make problem what can be more serious later. The car engine P1812 Code is found by the test of the car engine and following the right meaning of the car engine code, it becomes easier to fix the car engine. The general or automobile dictionary meaning of the code helps to know about the problem in general basis. The automobile dictionary meaning of the code is p for Powertrain Code Problem is related engine, transmission and emissions systems. 1 for MFG – Manufacturer Specific. 8 for Ignition System Or Misfire. 1 for Low Coolant Circuit and 2 for A/C System High Pressure High Temperature.