The Importance of a Good Output Speed Sensor
Your vehicle’s speed sensor, which is also called a vehicle speed sensor (VSS) or transmission output shaft speed sensor (OSS), tells your powertrain module how fast your car is traveling. This sensor is important for a lot of things, including regulating your speedometer and cruise control.
While the various speed sensors in your car have different functions, they all work in a similar way. They read a reluctor wheel or exciter ring that is mounted on whatever rotating equipment they are monitoring and produce an AC voltage signal to the PCM.
What is an output speed sensor?
Despite the name differences, speed sensors are all pretty much the same in modern vehicles. The Society of Automotive Engineers defines them as devices that measure the number of revolutions or distance traveled per unit of time and send that information to one or more onboard computers (also known as control modules).
There are two different speed sensors in your transmission: the input shaft speed sensor and the output shaft speed sensor. Both send their data to the powertrain control module of your vehicle. The PCM needs both input and output shaft speed data to calculate the correct gear ratio.
The input shaft speed sensor (ISS) and the output shaft speed sensor (OSS) are both magnetic pickups that provide transmission output shaft rotation speed to the powertrain control module of your vehicle. That data is used by the PCM to determine when to shift, adjust the torque converter clutch and display vehicle speed on the transmission-specific speedometer.
Both sensors work in the same way, using a reluctor wheel or exciter ring to read the speed of whatever they are monitoring. The PCM compares the readings from these sensors to the engine rpm data photosensitive sensor that it receives from the throttle position and crankshaft position sensor. If the speeds do not match, the PCM will set a trouble code in the diagnostic computer.
How does an output speed sensor work?
There are a few different types of speed sensors used in modern cars, including wheel speed sensors, camshaft position sensors and crankshaft position sensors. All of these sensors, despite their unique differences, function in the same basic way. A speed sensor uses a Hall effect sensor to read the movement of a reluctor ring that’s placed on whatever rotating equipment is being monitored. When the reluctor moves against a magnet in the Hall effect sensor, it creates a magnetic flux that varies the output signal of the sensor. This signal is then transmitted to the car’s onboard computer, which uses it to control other systems and functions.
The two transmission speed sensors in your car, the input shaft speed sensor and the output shaft speed sensor, are both a type of Hall effect position sensor. The transmission input shaft speed sensor and the output shaft speed sensors are both used to send rpm data to the powertrain control module so it can apply the correct gear ratio. Without the proper functioning of these sensors, your car’s automatic transmission won’t work correctly.
If one of the transmission speed sensors goes bad, your car might experience problems such as a rough or late shifting. A bad speed sensor can also cause your vehicle’s speedometer to display inaccurate readings. To prevent this, it’s important to replace a defective speed sensor as soon as possible.
What are the symptoms of a faulty output speed sensor?
A broken output speed sensor can cause erratic speedometer readings or even stop it from functioning altogether. Many systems in your vehicle depend on signals from the speed sensor, including the anti-lock braking system, ignition timing, transmission system, and cruise control. If you notice any of these symptoms, take your car to a professional mechanic right away.
You may also notice that your engine rumbles or idles irregularly when you start it, or that your car is burning more fuel than usual. This is caused by the engine control unit (ECU) receiving incorrect signals from the speed sensor.
Faults in the sensor can be caused by debris or dirt that has entered the case of the sensor, or by a loose connection. Moisture can also be a problem since it can affect the sensor’s ability to transmit signals.
It is important to make sure that your speed sensors are clean and free from debris. You can check them yourself using a multimeter. First, remove the sensor from its case. Find the black ground wire and the white signal output wire. Connect one lead of the multimeter to each of these wires, and set it to alternating current. Then, put a drill bit in the sensor’s gear slot until you hear it click into place to simulate a movement.
How much does it cost to replace an output speed sensor?
The speed sensor relays information about your vehicle’s rotational speed to the transmission control module, so the PCM can properly shift output speed sensor the metal gears of your transmission system. Without a reliable signal from the speed sensor, the PCM can cause improper shifts, which can damage the transmission and other car parts.
The cost of a new output speed sensor will vary depending on your specific make and model, as well as the labor rates in your area. However, a typical replacement should cost around $50.
As your car accelerates, the speed sensor detects the changes in rotational speed and sends this data to the transmission control unit, which then relays this information to your speedometer. A faulty output speed sensor can cause the speedometer to display inaccurate or erratic readings, which can be frustrating for drivers.
It’s important to replace a faulty vehicle speed sensor as soon as you notice any problems, such as trouble braking or odd sounds coming from the brake pedal. The longer you wait, the more expensive it will be to fix the issue.
Vehicle speed sensors are fairly durable, but they are subject to a lot of stress from road debris and other components in your vehicle. That’s why it’s important to check your speed sensor often for signs of wear and tear.
