Modern technology affects everything that we use. Almost every part of your car engine including the electronic engine control (ECC) utilizes information from the speed sensor. Depending on the make and model of the car some speed sensors are more refined and expensive. All they do is they give vital information on the engine speed of the car. You need to know that when a problem strikes, a faulty speed sensor can cause all manner of problems.

So what exactly is a speed sensor and what does a speed sensor do? Different types of vehicle speed sensors exist and are designed for different kinds of vehicle. In modern vehicles, the speed information is used to share information between the various car modules.

Always make sure that your sensor is giving the right information and is well synchronized with the car electronic engine control system. To fully grasp the vehicle speed sensor technology, we will have a look at how a speed sensor works.


What is a Speed Sensor

​A Vehicle Speed Sensor (VSS) measures vehicle’s speed. The sensor measures speed by calculating the actual gear ratio of the transmission while the car is in motion. Two sets of speed sensors are installed on every car to get the input and the output shaft speed.

​How does it Work

​The two synchronized sensors are not supposed to be out of alignment. If misalignment occurs, it may affect the operation of the car’s entire transmission. The data collected by the two transmission sensors is sent to the powertrain control module (PCM). The PCM will compare the two sets of readings and calculates the gear to engage for efficient driving.

The actual gear ratio reading is checked against the desired gear ratio. If the two ratios do not match the PCM will send an error code, and the check engine light will illuminate. If the readings are synchronized the car will move on to the next gear and your driving experience will be seamless.

How Does it Help

  • The Power steering gets its information from the Vehicle’s speed sensor for it to function properly. It regulates the power steering pressure at low speeds to make it easier to make quick manoeuvres, especially when slowing down or parking your vehicle.
  • The Anti-Lock Braking System (ABS) uses information from the speed sensors to determine if the wheels are locked up before releasing pressure from the wheels to maintain the stability of the car.
  • Cars with air suspension systems use the speed sensor readings to determine the ride height. This helps in lowering or raising the vehicle depending on the speed of the car, therefore, improves vehicle stability and handling.
  • Automatic transmission vehicles use the vehicle speed sensor to shift to the next gear automatically. This depends on the car’s transmission gear ratio readings while in motion.
  • While cruising, the cruise control system uses the sensor readings to activate or deactivate the system to maintain a constant speed.
  • All the electrical components of the system utilize the information coming from the seed sensors so that your car can function in an ideal atmosphere.

Speed sensors like any other car part are bound to fail or give wrong readings. For you to know if your problems are related to a faulty speed sensor, you will notice the following issues.

Improper Shifting

Gear shifting may be abrupt, rough, or faster than normal. An automatic transmission car is meant to have a smooth shift if everything is working okay. This bad gear shift can lead to failures of other components such as hydraulic lines and valves.

Improper Shifting

Cruise Control Fails

​When wrong readings are thrown out of the speed sensors the powertrain control module (PCM) will send an error code, and eventually shut down the Cruise control unit as a safety measure.

Cruise Control Fails

Check Engine Light Illuminates

When sensors fail, the PCM will throw an error code which will, in turn, illuminate the check engine light. You can use a vehicle diagnostic scanner to read and reset the error code. If the problem persists, do not hesitate to contact a certified mechanic to restore the speed sensors.

Check Engine Light Illuminates


Motor Vehicle Speed Sensors are either mounted in the transmission control or on the rear differential unit. The ones found in the transmission are gear driven, while the ones mounted on the differential are operated by the function of a trigger wheel mounted with the ring gear. Regardless of where the speed sensor is installed, they all perform the same task.

​Speed sensors are complex parts of the whole transmission system. When faced with the dilemma of a speed sensor error, having tried basic troubleshooting and it fails. Take your car to a mechanic who will probe it further. Share with us on what problems you encountered when your speed sensors failed by commenting and giving more views on what you think.

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Chief editor at Paul's Gigantic Garage. I came up with this blog to help you to sort out some basic problems your car may be facing and in turn, save lots of cash by some of my DIY tips that I hope will get your car out of its current situation. I also had in mind motor enthusiasts who for the love of cars who are constantly looking for information about cars on the latest trends, questions, fixes, driving, tricks, and accessories.


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