What is a Speed Sensor?

If you previously thought that speed sensors measured the speed of your car, well, we are sorry to let you down.

The speed sensors on your car actually measure the speed of the wheel rotations of your car while it’s driving. They do so by measuring the speed of the reluctor wheel which is located in the transmission.

In modern cars, there are two speed sensors:

Input shaft speed sensor: the ISS monitors the speed of the transmission input shaft
Output shaft speed sensor: the OSS measures the speed of the output shaft

No matter the location, speed sensors help the car’s computer decide when to shift gears.
Speed sensors are also important for maintaining stability, because they can tell the vehicle computer when to release pressure to a certain wheel while the ABS is activated.

In summary, they measure the actual gear ratio of the transmission while it’s in use. If the actual gear ratio is different from the desired gear ratio, then an error code will be activated and the check engine light will turn on.

If the sensors fall out of alignment, or experience other electrical issues, a similar error code will be activated, and the check engine light will turn on.

Common Symptoms of Speed Sensor Failure

The speed sensors in your car are very important. Because they help control the shifting of gears in your transmission, and the ABS, driving your vehicle with a bad speed sensor could mean that your car’s performance drops off drastically, or that the ABS system will malfunction, or not function completely.

Here is a list of things to look out for, as they might mean you need speed sensor repair:

• Speedometer stops function, or functions erratically.
• The odometer does not function.
• Car shifts gears roughly, or hesitates or jumps gears.
• The vehicle idles incorrectly.
• Cruise control does not function.
• The vehicle rumbles, or suddenly loses power.
• The check engine, brakes, or ABA warning lights are illuminated.

If your car has any of these symptoms, it could mean that the speed sensors need repair. Although your car will still operate with malfunctioning speed sensors, it is not recommended that you delay with this repair.

Failed speed sensors will worsen over time, and will affect the performance of your car. After a while, due to their important role in the ABS of your vehicle, driving your car could become a safety hazard.

How To Fix Broken Speed Sensors

First, a complete diagnostic test will be run on the car. The reason being that a failing transmission also causes similar symptoms to failing speed sensors. Essentially, the mechanic needs to diagnose for certain that the issue you are having is with the speed sensors.

Once they have determined the problem is indeed related to the speed sensors, they will execute the following steps in order to replace the speed sensors:

1. The car battery is disconnected, and the car is jacked up.
2. The malfunctioning speed sensor is located and removed.
3. A brand-new speed sensor is installed and connected.
4. The vehicle is lowered, and another diagnostic check is performed.
5. The vehicle is test-driven and scanned for proper operation of the new sensors.

If your car has been driving badly, and some symptoms from above sound familiar, we recommend you schedule your car for service. If you enjoyed this article or learned something new, let us know. We would love to hear from you!