Understanding Your Car’s Speed Sensor
In most cases, you’ll probably never need to think about your vehicle’s speed sensor (VSS). Like most of the parts and systems under the hood, as long as it’s working properly, you can basically forget about it. Plus, the VSS typically won’t wear out over time, so it won’t usually need to be replaced like a car battery, air filter, or spark plug. That said, it can malfunction. When it does, the failure will affect either your cruise control, speedometer, or anti-lock brake system (ABS).
Below, I’ll briefly describe what your vehicle’s speed sensor does and how it works. After reading this article, you’ll understand why it’s a critical element that plays an important role in how your car preserves your safety on the road.
What Does A VSS Do?
In a nutshell, it monitors how fast your car is moving. It accomplishes this through the use of electrical pulses. Specifically, the unit produces a series of pulses based upon the speed at which the wheels are turning. Those pulses are delivered to a central computer. The computer monitors the rate at which wheels are turning in order to adjust the output of the speedometer and cruise control system.
Technically, the VSS is normally positioned on the transmission. Separate monitors are attached directly to the wheels (referred to as “wheel speed sensors” or alternatively, WSS). It’s the WSS that monitors the rate of the tires and reports the data to the computer which controls the anti-lock brakes.
Now, let’s focus on the anti-lock brakes for a moment. The purpose of the system is to prevent the brakes from locking up. The WSS helps the ABS by identifying variations in the individual wheel speeds. If they’re spinning at different rates, that implies a lock-up. With that data (delivered by pulses from the WSS), the computer can make modifications in order to compensate.
What Happens When It Fails?
If the VSS or WSS malfunction, it can cause your car’s speedometer to output inaccurate data. For example, you might be traveling at 55 mph, but your speedometer may only indicate 20 mph. Also, your vehicle’s cruise control will likely malfunction. Remember, the computer adjusts the cruise control in order to maintain how fast your car is moving. If it is receiving inaccurate data (or no data at all), it won’t be able to make the necessary adjustments. Finally, the anti-lock brakes won’t be able to perform their job as effectively since the WSS is outputting bad data.
The first sign of a malfunctioning VSS will be your speedometer. If you notice that it is implying speeds that are obviously inaccurate, ask your mechanic to check both the VSS and WSS. As noted above, these components don’t normally malfunction. But, when they do, it can impact your safety.
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