Scheme for checking the speed sensor
1. Connect (+) batteries with 1 sensor output, and (-) battery terminal 2. (+) connect the output of the voltmeter to terminal 3, and (-) voltmeter output - with output 2, according to the diagram.
2. Turn the shaft - the voltmeter should show a voltage ranging from 0 to 11 V 4 times per 1 revolution. Otherwise, replace the sensor.