A faulty speed sensor shouldn't be ignored as it can cause transmission and drivability issues. It can also make the .Check Engine. light turn on. But not all vehicle speed sensor problems call for replacement, so it's a good idea to test the sensor first before deciding to replace it with a new one.
In case you need a little help, here are the steps on how to check the sensor and how to replace it the moment you find out that it is really the culprit:
What you'll need:
- Jack stands
- Wheel blocks
- Voltage meter
- New speed sensor (if necessary)
Step 1: Raise the vehicle.
Park the vehicle in a flat, level ground, turn the engine off, and employ the emergency brake. Allow the vehicle to cool down completely.
Get the wheel blocks and position them around the rear wheels. Go in front of the vehicle and raise it using a jack. Securely lower it onto the jack stands, making sure there is enough space for you to slide underneath the vehicle, on your back.
Step 2: Locate the speed sensor.
The sensor, which is a plug-type part with an electrical connector on its side, is usually screwed in the passenger side, to the rear section of the transmission. But since the location of a transmission output speed sensor may vary from one vehicle to another, it is wise to check your repair manual first to know its exact location in your model.
Step 3: Check the signal from the computer to the sensor.
To do this, you have to unplug the sensor's electrical connector from the wiring harness and detach the harness. Put the ignition to the .ON. position. Without starting the engine, insert the probes of the voltage meter. Take note of the voltage output at the connector; it should produce at least 5 volts. If you fail to record any voltage, then there sure is a problem with the signal coming from the on-board computer. If this is the case, the vehicle needs to be serviced by its dealer and checked using the appropriate diagnostic equipment.
If the on-board computer isn't the culprit, proceed to the next step.
Step 4: Take out the speed sensor.
Detach the electrical connector from the sensor and take out the sensor from the transmission. Depending on the vehicle, you can remove the sensor by either loosening the bolt that secures it to the transmission or turning the sensor counterclockwise until it is released.
Step 5: Check the sensor.
Put the sensor on a flat surface and slowly turn it by hand. Check for the pulsing AC voltage using the voltage meter. It should record from 0 to 0.5 volts. Absence of voltage indicates a defective sensor.
Step 6: Install the new sensor in place.
Set the new sensor where the old one is positioned. Secure it by either putting back and tightening the bolt that holds it to the transmission or turning the sensor clockwise until it's tight.
Step 7: Finish off the speed sensor installation.
Reconnect the electrical connector by pushing it in place until it clicks. Get out from underneath the vehicle and lower the jacks until the wheels now touch the ground.