How to Test for a Bad Vehicle Speed Sensor

What You'll Need
Multi Meter
Scanning Tool

The vehicle speed sensor sends a signal to the onboard computer about the current speed of the vehicle. A vehicle speed sensor that is defective can cause serious problems with the way that the car operates. These problems are not only attributed to the speedometer. You will see problems with the cruise control, transmission, ABS, and even power steering problems. Here are some ways to test the vehicle speed sensor to determine if it is faulty. 

Step 1: Check Sensor Reluctance

There are two ways that you can determine whether a variable reluctance sensor is bad. The first way is by checking the Ohms that the sensor is relaying. If you notice some resistance then the winding is good. Another test is to plug in a scanning tool directly into the car's computer. Drive the vehicle and monitor the data that is being sent by the sensor. 

Step 2: Test Sensor Mag Resistive

If your car has a magneto type resistive, there are digital signals that are sent to the car's computer. To test this type of sensor you will need to use a scanning tool again. You can also do this manually by unplugging the sensor and turning the key to "on". Use a meter to see if there is any power going to the sensor's cable under the transmission.