Control method for output signal of automobile urea quality sensor

The invention relates to an automobile urea quality sensor output signal control method, which comprises the following steps that a urea quality sensor is arranged in a urea box, and a certain amount of urea solution is filled in the urea box; a power supply of the urea quality sensor is switched on, and the urea quality sensor works normally and records voltage energy signals converted from five continuous ultrasonic echo signals; if the number of the energy signals higher than the threshold value line in the five signals recorded continuously is larger than or equal to 3, it is judged that the output signals of the sensor are reliable, and the ECU outputs the actually-calculated urea concentration value, and if the number of the energy signals higher than the threshold value line in the five signals recorded continuously is smaller than or equal to 2, it is judged that the output signals of the sensor are not reliable, and the sensor outputs invalid signal codes; and the electronic control unit ECU outputs