| 摘要 |
PROBLEM TO BE SOLVED: To provide a urea water concentration erroneous diagnosis prevention system which can prevent the erroneous diagnosis of a urea water concentration caused by foams.SOLUTION: When detecting a urea water concentration in a urea water tank 16 at an ultrasonic propagation velocity, the urea water concentration is repeatedly detected in a stationary state and a transition state of an operation of an engine, the maximum urea water concentration in each state is stored, normality and abnormality are sequentially detected by comparing the maximum urea water concentration which is stored at the switching of the states and an abnormal threshold, and the normality and abnormality of the urea water concentration is determined from a determination result of the normality and abnormality of the continuous past states. |
