Speed Sensor Buyer's Guide
- The data displayed and used by different electronic systems in your car are collected by the vehicle’s speed sensors.
- Speed sensors are the small components that collect information about how fast a vehicle is going.
- There are two types of mechanisms used in automotive speed sensors: Reed switch and Hall Effect mechanisms.
- There are two types of speed sensors: transmission speed sensors and ABS speed sensors.
- Symptoms of a faulty speed sensor include sluggish or poor gear shifting; erratic speedometer and odometer readings; activated warning lamps; and defective cruise control systems.
- To find the right speed sensor, consider types of vehicle speed sensors, tire sizes, and whether you should get an optical speed sensor or a permanent magnet.
- OEM replacements are sold individually and may cost you anywhere from $30 to $2,800.
One of the key factors for road safety is knowing how fast your vehicle is going on the road. When we think about speed, the first thing that comes to mind is a vehicle’s speedometer. But have you ever wondered where your car gets the information it displays? The data displayed and used by different electronic systems in your car are collected by the vehicle’s speed sensors.
What is a speed sensor?
Speed sensors are the small components that collect information about how fast a vehicle is going. Both manual and automatic cars rely heavily on these sensors to improve their efficiency and drivability.
These sensors are located on the transmission output shaft or the crankshaft, on the transmission case, within the rear differential assembly, or inside the ABS system. Each vehicle typically has more than one-speed sensor which has a specific role in keeping your vehicle safe on the road. Let’s dig deeper into what these sensors are and how they work.
How do speed sensors work?
There are two types of mechanisms used in automotive speed sensors: Reed switch and Hall Effect mechanisms.
Reed switch sensor
A reed switch sensor is basically an electrical switch that turns off when a magnet comes near it and switches back on once the magnet is pulled away. In vehicles, a magnetic sensor has three parts: a magnetic coil, a detector and a toothed metal disk connected to a shaft.
As your car moves, the disk spins and its teeth move past the magnetic coil which causes the magnetic field to switch off. These create magnetic pulses that are used to compute vehicle speed based on pulse frequency.
Hall Effect sensor
Named after American physicist Edwin H. Hall, this type of sensor also detects interruptions to the magnetic field to calculate speed. Unlike reed switch sensors, these sensors do not have any moving parts.
Hall Effect sensors are typically placed on every wheel or axle. Each component is made up of a sensor and a permanent magnet. Every time the magnet is perpendicular to the sensor, a voltage proportional to the wheel’ is generated.
Types of speed sensors
There are two types of speed sensors: transmission speed sensors and ABS speed sensors.
Transmission Speed Sensor or Vehicle Speed Sensor
There are two types of transmission speed sensors: the output shaft speed sensor and the input shaft speed sensor. Both types are commonly found in vehicles with automatic transmissions. They come in pairs order to get an accurate reading of your vehicle’s speed which is relayed to the car’s powertrain control module.
Output Shaft Speed Sensor
The transmission output shaft speed sensor (OSS) relays information to the vehicle’s control module about how fast the car is going. The data collected from this sensor is used by your vehicle’s speedometer and odometer.
Input Shaft Speed Sensor
The transmission input shaft sensor (ISS) collects information on the rotational speed of the torque converter or the input shaft. This sensor detects the transmission’s internal revolutions and sends this data to the car’s power control module. This information is used to determine which gear should be engaged for efficient driving.
ABS Speed Sensor or Wheel Speed Sensor
The Anti-Lock Brake System speed sensor collects information on wheel rotation and uses this to calculate the vehicle’s speed. These are Hall Effect sensors that convert information into digital signals that help tell the ABS system when to engage and disengage brakes.
Why should faulty speed sensors be replaced?
Damaged speed sensors cannot be repaired, only replaced. Unlike other automotive parts, there’s no specific interval for its replacement which can make it difficult to determine when it needs to be replaced. Due to its moving parts, transmission speed sensors may be prone to breakage. At the same time, ABS sensors are also prone to wear because of its location on the wheels. If you notice one or more of these signs, you may need to get your speed sensors checked by a mechanic.
Sluggish or poor gear shifting
The lack of data from your car’s speed sensors can cause delays in switching between gears.
Erratic speedometer and odometer readings
A faulty transmission speed sensor can cause your speedometer and odometer to malfunction because it relies on consistent speed information.
Check if the Engine Light, brake, or anti-lock warning lamps are switched on
Two or more of these warning lights switching on at the same time means there is a high possibility that your car is having trouble with its speed sensors.
Cruise control systems stop working
Without information about the car’s speed, the cruise control system will not be able to maintain the car at the same velocity.
The information collected by your car’s speed sensors is used by multiple systems in your car. The Variable Assist Power Steering (VAPS) system uses data from the VSS to regulate power steering for higher assist at slow speeds. Advanced air suspension systems also use this information to adjust ride height for better handling at different speeds. Therefore, it’s important to have your car’s speed sensors replaced as soon as it fails.
What to consider when choosing a speed sensor
Your speed sensor affects the operation of multiple systems in your car. Not only does it help you stay within the speed limit, but it also helps your car react better and faster to your driving. So don't be reckless when choosing new sensors for your car. Here are some things you should take note of when buying speed sensors:
Types of vehicle speed sensors
There are basically two types of speed sensors, the engine speed sensor and wheel speed sensor. Although both types do the same job (a.k.a. read data and feed it to either the speedometer or anti-lock brake system), the type of speed sensor you need to buy will depend on the symptoms that you notice on your car. Does your car go through intermittent stops without stepping on the breaks? Then that means you need to change your wheel speed sensor. Is your speedometer reading incorrectly? Then a faulty engine speed sensor might be the cause. Before you go to an auto parts center to get a new speed sensor, be sure that you know which of the two types your car needs.
Optical speed sensor vs. Permanent magnet
After identifying which type of speed sensor to replace, another thing to consider when buying a new one is its material. The conventional style of speed sensor makes use of an optical VSS. This optical VSS is made up of a photo cell, LED, and a two-blade mirror reflector to generate electrical signal, which in turn electronically measures speed. This kind of speed sensor is commonly used and is available for almost all makes and models. But because of the optical speed sensor's moving parts, it is more prone to mechanical wear. If you're looking for a speed sensor that's more reliable, installing a permanent magnet speed sensor is a better choice. It detects speed, direction, and position more accurately than an optical sensor, and its non-contact with the target provides enhanced reliability and an extended life.
Tire size can also affect the efficiency of your speed sensors. If you've upgraded to a bigger tire size than your OE tires, it is advised to recalibrate your tires before installing a new speed sensor. The difference in tire sizes may cause the wrong speedometer sensor readings, which can eventually affect your speed sensor signals.
How much are replacement speed sensors?
The cost of speed sensors varies depending on the vehicle year, make and model. OEM replacements are sold individually and may cost you anywhere between $30 and $2,800. Speed sensor prices typically vary based on the vehicle’s make and model. While it is possible to replace speed sensors on your own, we recommend going to a trusted mechanic.
Installing a Speed Sensor on Your Car
Do you see a tiny orange light blinking in your dashboard? Is your speedometer going haywire? Does your car switch gears at the wrong times? If you answered yes to all these questions, then your car has gotten a mind of its own due to a faulty speed sensor. Replace your speed sensor before your car goes Decepticon on you and causes more problems on the road. Here's a DIYers guide to help you replace your speed sensor with ease.
Difficulty level: Moderate
Things you'll need:
- Speed sensor replacement
Step 1: Prepare the car. Lift the front of your car using a jack and jack stands. Create a wide space that will let you slide underneath. Look under the passenger side of your car and locate your car's transmission.
Step 2: Locate the speed sensor. Your speed sensor should be screwed into your transmission. It is usually located to its left. Once you've seen a plug-type component with an electrical connector on the side, you've found your speed sensor.
Step 3: Prepare the speed sensor for removal. Remove the electrical connector from the speed sensor. Using the ratchet and an appropriately sized socket, you then remove the bolt on the sensor. Pull the sensor towards you to gain easier access to your sensor.
Step 4: Remove the old speed sensor. Twist the sensor counter-clockwise to loosen it from the transmission. Grasping the sensor with a wrench, remove it from the transmission and discard it.
Step 5: Install a new speed sensor. Place the new sensor into your transmission. Snap the clips that connect it to the transmission. Secure the new speed sensor into place until it clicks.
Step 6: Add the finishing touches and tes the new speed sensor. Your new speed sensor is now in place and ready for use. Slide it away from your vehicle and lower it to begin testing your new sensor.