You should be careful if your car is faulty and you should check the car for solving the problem of the B1721 Code. This code comes on the code reader of the engine. While car engine is diagnosed, then the car code comes and you should solve the problem. You can solve the problem if you have experience and have all machines. The dictionary meaning of the code is B for Body Code Problem is antilock brake system, electronic suspension and steering systems. 1 for MFG – Manufacturer Specific. 7 for Auxiliary Emission Controls. 2 for Air Conditioning Clutch Feedback Circuit High Voltage and 1 for TFP Valve Position Switch-Drive Without Drive Ratio.