What are the Symptoms of a Failing Transmission Speed Sensor?

1. Cruise Control Fails

The main function of the speed sensors is to monitor the output and input shaft speed. But that's not the only function of these sensors. They also check cruise control. Cruise control is a system that controls the vehicle's speed automatically. Its proper functioning depends on the data from the transmission speed sensors. If it fails to work, then it means the sensors have malfunctioned. The PCM will transmit an error code to ECU, which will shut down. If that happens, it would be better to contact your mechanic immediately to have your vehicle checked.


Here’s How to Test Your Transmission Speed Sensors

Let’s do this!

Testing Transmission Speed Sensors

  1. Using an OBD2 scanner, check to see if there are any error codes related to the transmission speed sensor.
  2. If there are, there’s your problem. The part will need to be replaced.
  3. If there aren’t any codes, or if your car is from the Regan years, you’ll need to physically test the sensor.
  4. For better clearance, lift up the front end of your vehicle.
  5. Locate the transmission speed sensors, they’ll be near the front and rear of the transmission housing. Consult the repair manual for your car.
  6. Place bucket or oil drain pan underneath the sensor, there will be some oil that drains out.
  7. Disconnect the sensor from the housing on the transmission, as indicated in the repair manual for your car.
  8. Disconnect the sensor’s wire coupling.
  9. Turn the key to the ignition on, but engine off, position (one key click past Accessory)
  10. Using the multimeter’s voltmeter connect the probes to the ground and reference wires in the connector.
  11. If no voltage is received, the sensor is faulty.  
  12. If voltage is received, you may need to have the car diagnosed by a qualified tech.

Replacing Your Transmission Speed Sensors 

  1. Having found the sensor or sensors to be faulty, remove the connector between the sensor and the vehicle’s wiring.
  2. Using the proper socket, remove the faulty sensor.
  3. Connect the new sensor to the vehicle’s wiring.
  4. Install the new sensor.
  5. Lower your car.
  6. Start the engine.
  7. Take a test drive.
  8. Check to make sure the transmission shifts properly.
  9. Check to make sure the cruise control works properly.
  10. Wait to see if the check engine light goes off.
  11. If everything is a-ok, you’re golden. 

Congrats, you did it!


Next Step

Schedule Vehicle Drivetrain Inspection

The most popular service booked by readers of this article is Vehicle Drivetrain Inspection. Once the problem has been diagnosed, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. YourMechanic’s technicians bring the dealership to you by performing this job at your home or office 7-days a week between 7AM-9PM. We currently cover over 2,000 cities and have 100k+ 5-star reviews… LEARN MORESEE PRICING & SCHEDULING

2. Cruise Control Does Not Work

Since the transmission speed sensors monitor the input and output shaft speed, it also plays a part in monitoring the cruise control. When the sensors fail to deliver accurate data to the onboard computer on your car, truck, or SUV, the powertrain control module (PCM) will send an error code to the vehicle’s ECU. As a safety precaution, the ECU will shut down the cruise control and render it inactive. If you notice that your cruise control does not engage when you press the button, contact a mechanic so they can inspect the vehicle and determine why the cruise control is not working. It may be due to faulty transmission speed sensors.

How Often Do You Need To Test Your Transmission Speed Sensor?

Automakers build these sensors with a long lifecycle, the only reason you’d need to test or change the transmission speed sensor would be because it began to malfunction again. 


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