You need to know the exact meaning of the engine C1921 Code and the right meaning of the code is a necessary thing for fixing the car engine problem. You can easily find the meaning online but do not allow automobile dictionary meaning for solving the car engine problem. However, you can fix the car engine problem if you have all tools and expertise for solving the car engine problem. Do not follow wrong meaning of the code for your car engine. You must find the engine code related with your car manufacturer. Do not drive the car with any problem in the car engine.