The C1721 Code is related with the car engine and meaning of the code helps to identify the real meaning. Solving the car engine, you need to get the meaning of the code properly. Like the all car engines, this car engine method works specifically established hydraulic lifters what known as switching roller followers for the engine C1721 code intake and drain valves. The lifters can be distorted by disengaging an inner locking pin. The locking pin is detached using solenoids to change oil compression fed into the lifter. After fixing the car engine, take the car for a test drive.