While you may not know, transmission speed sensors are vital devices in the smooth running of your modern car. In this article, I will talk about the transmission speed sensor connector, its types, how it works, and faulty symptoms.
What Is Transmission Speed Sensor?
Transmission speed sensors are small electronic devices you mount on an electrical connector in your transmission. The other end of the sensor is connected to car computers such as the ECM and PCM.
The main purpose of the speed sensor is to measure the rotational speed of different transmission parts. After it gathers this data, it sends it to your car computer.
Then, the ECU analyses this information and uses it to regulate and adjust the parts that make your vehicle move. Some of these parts include your ignition and injection timer, combustion chamber air-fuel ratio, and the shift points of the transmission.
Other Functions of the Transmission Speed Sensor
In addition to speed checking, if you’re using an automatic, the sensor tells your car transmission when to change gears. It also helps the engine alert some parts, such as the anti-locking system and ABS, when to act. This phenomenon mostly happens when one of your car wheels rotates faster than others.
Also, the sensor helps your speedometer and odometer get the correct speed and distance readings, respectively.
Note that your car generally has two transmission speed sensors. One for the shaft input speed and the other for its output speed.
Your car ECU must get the reading of these computers, to compare them to determine an accurate action. If one fails, you can expect an improper functioning of the entire transmission.
A car speed sensor
Types of Transmission Speed Sensor
While there may be many types of speed sensors, I will discuss the main two, plus their pros and cons.
Magnetic Transmission Speed Sensors
Also known as reluctor sensors, magnetic sensors use magnetism principles and are the oldest. They feature a coil and a magnet, which you attach to your car transmission or any rotating object. Once your car transmission shaft rotates, the attached magnet also rotates. This rotation of the magnet creates a magnetic field that generates a current of a certain voltage to the coil. Here, the magnetic voltage created is equivalent to the speed of the transmission rotation. This sensor type is simple, reliable, and cost-effective. However, signal interferences can affect it, and it’s not very accurate at low speeds.
Hall Effect Transmission Speed Sensors
Then you have Hall Effect sensors, which are the newest in modern cars and use the Hall Effect. Instead of a metallic coil, they have a semiconductor chip to detect changes in magnetic field, plus a magnet. When transmission rotates, the magnetic field changes, generating a current on the chip. Your system then uses this voltage to know how fast your transmission rotates. Such sensors are very accurate even at low speeds, and interferences do not affect them much. But, despite their accuracy and reliability, they are more expensive than the magnetic type.
A type of rotational sensor
How Does the Transmission Speed Sensor Work?
Despite there being two main types of transmission speed sensors, their working principle is the same.
As we established earlier, it measures the input or output speed rotation of the transmission. An input or output transmission speed sensor usually comes with a gear that rotates as the shaft does.
Then it also has a magnet sensor to detect the rotation of this gear.
As your transmission rotates, it also makes the attached sensor gear rotate. This effect creates a varying magnetic field that the sensor detects.
Consequently, the resulting magnetic field produces voltage signals of different frequencies and sizes depending on your transmission speed.
Your sensor interprets this voltage as your car’s speed and sends it to your computer, making other parts act accordingly. For instance, if the speed is high, the ECM increases fuel injection for more power.
How to Test Transmission Speed Sensor
Like any other part, your transmission sensor can also run into problems that may prevent your car from running smoothly. Luckily, I have researched and scripted some steps you can use to test it. But before then, you must have some tools and materials to make your work easier. Some of the tools you may need include:
- Jack and Jack stands
- Protective gear such as goggles and gloves
- Multimeter gauge
- Service manual for your car model
Ensure safety
Trusting you have all the materials, your very first step before you can run the test is to ensure safety. You need to start by parking your car on flat/level ground and engaging the parking brake.
Then, wear your protective gear, such as goggles, an apron, and gloves, to prevent accidents. Lastly, disconnect your car battery to prevent any hazardous shock or short circuits.
Disconnect your sensor
Once you adhere to my safety recommendations, disconnect the sensor from the transmission. Be careful not to damage the sensor or bend and twist its wires. Inspect it for corrosion of its terminals or any visible damage when through.
Use a multimeter to test it.
As you may know, a multimeter tests the continuity or resistance of a wire or a device. Therefore, I hope you gathered it so that you can use it to know your speed sensor status.
First, use the multimeter knob to set it to Ohm/ resistance measurement. Then check your car manual to know the resistance range you should expect from your sensor Ohm reading.
From there, connect the multimeter probes with the two terminals of the sensor and observe the reading on the display.
If the resistance range you get on the screen does not coincide with the range from your manual, then your device is faulty.
Here, I recommend consulting a mechanic for repairs or replacement. However, if the Ohm reading is ok, go to the next testing step.
Using a multimeter
Check the wiring
Like all other systems in your car, the speed sensor connects to other systems via a wiring harness. For this reason, if it’s not functioning, you need to check the connected cable. Look for damage, fraying, sharp bends, cuts, exposed conductors, or general wear and tear. If your speed sensor wiring has an issue, you must replace it to ensure accurate sensor function.
Clear error codes
Remember that a faulty sensor may show indications such as the check engine light. Unfortunately, these errors do not disappear just because you uninstalled the speed sensor. For this reason, you have to clear them using an OBD-II scanner. The device clears error codes and resets your car computer, ensuring proper monitoring.
An OBD scanner
Reconnect the sensor and test
After you have addressed your sensor wiring issues, you will have to reconnect it to its original position. Remember, you may also change the sensor, but buy a compatible one. When reconnecting, ensure it’s tight and snug enough to prevent it from coming off and other resulting issues. Take your car for a ride to ascertain its wiring is functioning properly. While driving, pay attention to shifting smoothness and ensure there is no check engine indicator light.
What Are the Symptoms of a Faulty Transmission Speed Sensor?
The most common symptom you can expect from a faulty speed sensor is transmission issues. For example, you may experience abnormal gear operation, plus hard and delayed shifts.
Then, you may notice your check engine light illuminating when the sensor sends an incorrect reading to the ECM.
Another problem is inaccurate speedometer reading, or the device stops working altogether, which can spell safety problems. Also, if your car has ABS, you may notice it malfunctioning or not engaging.
Lastly, it may cause the cruise control to stop functioning and idle stalling in some cars.
Conclusion
I believe you can use my research to know how your speed sensor works and also how to check if it’s functional.
