If the car engine has any problem, you need to fix the car engine and if the car engine is checked and found the engine U1231 Code, you should allow the meaning of the engine code. The engine code is important thing for solving the car engine problem. The automobile dictionary meaning of the code is u for Network Code Problem is climate control system, lighting, airbags, etc. 1 for MFG – Manufacturer Specific. 2 for Accelerator Pedal Position (APP) Sensor 1 Performance. 3 for Cruise Control Servo Indicates Low and 1 for TFP Valve Position Switch-Drive Without Drive Ratio.