2020 Subaru Legacy Speed Sensor

What is a speed sensor and what does it do?

Imagine driving down a winding road, the wind in your hair and your favorite song playing. But how do you know you're cruising at just the right speed? Enter the speed sensor—a small yet mighty component that plays a pivotal role in your driving experience. This clever device measures how fast your vehicle is traveling and sends that information to the engine control unit (ECU) and various other systems. Without it, your speedometer would be little more than a decorative dial.

But the speed sensor does much more than just keep tabs on your speed. It’s like the conductor of an orchestra, ensuring that different parts of your vehicle work in harmony. For instance, in automatic transmissions, speed sensors provide critical data to the transmission control module (TCM). This allows for seamless gear shifts, making your ride smoother and more efficient. And when it comes to safety features like anti-lock braking systems (ABS), the speed sensor is a hero in disguise. It constantly monitors wheel speed, preventing lock-ups during sudden stops and helping you maintain control in slippery conditions.

Types of speed sensors

1. Wheel speed sensors
Located at each wheel, these sensors monitor wheel rotation and are vital for ABS and traction control systems.

2. Transmission speed sensors
Found in the transmission, they measure the speed of input and output shafts, aiding in optimal gear shifting.

3. Vehicle speed sensors (VSS)
Often mounted on the transmission, they provide overall vehicle speed data to the speedometer and ECU.

4. GPS speed sensors
Use satellite signals to determine speed, commonly found in navigation systems.

Symptoms of a bad speed sensor

The signs of a bad speed sensor are crucial indicators that can significantly affect vehicle safety and performance. These signs highlight the importance of proactive vehicle maintenance and the need for drivers to be attentive to their car's behavior. Here are the key issues you might encounter:

• Erratic speedometer: An inaccurate speedometer can lead to unsafe driving practices, as you May not be aware of your actual speed, increasing the risk of accidents.
• Transmission issues: Rough or delayed shifting can indicate deeper transmission problems, which, if left unaddressed, can lead to costly repairs.
• Check engine light: The activation of this light is a crucial alert from the vehicle’s diagnostic system. Ignoring it can result in more severe engine or system failures.
• ABS problems: Malfunctions in the ABS can compromise braking safety, making it critical to address speed sensor issues promptly.
• Decreased fuel efficiency: Poor fuel economy affects not only your wallet but also increases emissions, making it an environmental concern.