How to Check a Speed Sensor


You can save a lot of money in the long run by testing a 2 or 3-wire (Hall Effect) speed sensor yourself. Your car may begin to behave as though it has a faulty coil pack or throttle position sensor, and even after testing those components, you may still come up empty-handed. This is when you should test your two or three-wire speed sensor, as malfunctioning ones can also cause these problems. Another reason to test your 2 or 3-wire speed sensor is if your speedometer is functioning strangely or does not work at all.

How to Check a Speed Sensor

The guys at Autometer put created a couple of movies that walk you through the produces for each to demonstrate how to test a 2 or 3 wire speed sensor. There aren’t many tools required for the test, and they aren’t particularly specialized. A multimeter with clamp leads and a drill are the only instruments required to test a 2 or 3-wire speed sensor. The 3-wire speed sensor is externally powered; therefore, you’ll need some kind of power supply.

The two-wire speed sensor is tested first. These sensors are self-powered, which means that the revolutions inside the case generate the signal required to move the speedometer. They begin by connecting the red wire to the signal output and the ground lead (black) to the speed sensor’s ground. Because he is testing the 2-wire speed sensor outside of the car, he uses a high-powered drive device (a drill) to spin the sensor at the required RPMs to get a signal. If you want to test the vehicle, you’ll need to drive the wheels using the engine to generate enough RPMs to generate a signal. (DISCLAIMER: We do not advocate driving the vehicle anyplace if the speedometer is not working.) Using the drill to run the sensor demonstrates that as the drill’s RPMs grow, so does the voltage output of the sensor. This indicates that the sensor is working appropriately.

It is nearly as straightforward to test a three-wire (Hall Effect) speed sensor. Because the 3 wire sensors are externally powered, you’ll need a power supply of some sort if you’re testing outside of the vehicle. You’ll still use the clamp leads with your multimeter, and after connecting power and ground, you’ll connect the ground (black) lead to the external source ground and the red lead to the sensor’s output.