This code C1906 is a common code in many car engines and it is necessary to find the real meaning of the code. You may find the real meaning of the code from online and in the car engine manual. This same code has different meanings what you may find also online. Do not follow those wrong meaning of the code for solving the car engine problem. You must find the real meaning of the code what is linked with your car. Your car developer has set that meaning. Other car manufacturers have set meanings of the code what you must not follow for your car engine.