The meaning of the C1221 Code is helpful but make sure that you have used correct method for finding the right meaning of the code. Do not worry if you do not how to find the meaning. An automobile engineer knows how to find meaning of the code. An automobile engineer finds the meaning of the code related with the model and brand. The automobile dictionary meaning of the code is C for Chassis Code Problem is controller area network wiring bus and modules. 1 for MFG – Manufacturer Specific. 2 for Accelerator Pedal Position (APP) Sensor 1 Performance. 2 for Air Conditioning (A/C) Clutch Feedback Circuit High Voltage and 1 for TFP Valve Position Switch-Drive Without Drive Ratio.