Speed Sensor Check

Jack up front of car and support with safety stands. Block rear wheels and set parking brake.
Connect voltmeter positive probe to yellow/black wire terminal at control box connector. Connect negative probe to a suitable ground.
Start engine. Select second gear and accelerate slowly while observing voltmeter.
Voltmeter should show battery voltage above 20 MPH. Below this speed, no voltage should be shown.
If voltage is present at the wrong speed, replace speed sensor. If no voltage is present, check fuse and related wiring and repair as necessary.