Wheel speed sensors are essential vehicle components that ensure stability, safety, and performance. The main function of the sensor is to monitor the rotational velocities of each wheel, and this information is transmitted to the car’s electronic control module.
Wheel speed sensors form a crucial part of anti-lock brakes, preventing the potential of accidents by detecting when the wheels lock up following emergency braking. Though wheel speed sensors are critical to vehicle safety, they are also susceptible to different factors, including corrosion, dirt, debris, and electrical issues.
When a wheel speed sensor fails, the ABS warning light comes on, meaning the anti-lock braking system needs to be checked out.
What is a Wheel Speed Sensor?
Typical wheel speed sensors consist of a coil of wire set around a soft iron core. The coil is also connected to a permanent magnet. The sensor is close to the trigger wheel attached to the wheel hub or the drive shaft. When the wheel rotates, the resulting movement from one tooth to the other varies the magnetic field, which induces an alternating voltage in the sensor coil. The frequency of the induced voltage is also proportional to the wheel speed generated.
The vehicle speed from the wheels is transmitted to the Electronic Control Unit. It feeds the safety system, odometer, and speedometer with the relevant information. Wheel speed sensors must remain within the same position to accurately detect the speed at which the tires are moving. They are generally mounted on the stationary portion of the hub assembly and pointed at the reluctor ring. This timing ring has toothed gears in the rotary part of the hub assembly.
How Long Do Wheel Speed Sensors Last?
Wheel speed sensors are typically made to last as long as the vehicle. Considering the rough conditions they may operate in, though, it can be difficult to maintain them for lengthy periods. For example, the heat produced by the engine will make the wires brittle, so the sensor may fail over time due to wear and tear.
How To Tell if a Wheel Speed Sensor is Bad?
Wheel speed sensor failure can occur because of increased wear or other environmental damage. However, there are different symptoms of problematic wheel speed sensors. For one, an ABS sensor symptom is the warning light on the dashboard. The light may flash briefly whenever the vehicle starts. However, if the speed sensors in the ABS are faulty, they may stay on until they are replaced. Traction and stability control problems also indicate a problematic wheel speed sensor.
When the wheel speed sensor malfunctions, these systems shut down because they send data to the traction and stability control. Faulty wheel speed sensors may also lead to uneven braking as they contribute to operating the anti-lock braking and traction control systems. Problematic sensors can signal incorrect wheel sleep, making the system incorrectly assess or reduce braking on one or more wheels.
This can be dangerous depending on the driving conditions, especially in rain or snow. Failing wheel speed sensors also lead to incorrect speedometer readings, as the data transmitted from the hub is inaccurate. Incorrect speed assessments may confuse the driver, making them improperly judge traffic flow or driving distances, increasing the potential for accidents.
Diagnostic tools like an OBD-II sensor are essential for identifying potential risks posed by a problematic wheel speed sensor. The tool can quickly determine which sensor component is the problem, and codes issued indicate the exact location of the fault. Identifying sensor issues early on may also prevent accidents or further damage to the ABS.
What Causes Wheel Speed Sensor Failure?
Wheel speed sensor problems typically occur for various reasons, including physical damage, environmental factors, or wear and tear.
Accumulation of Dirt and Debris
One of the most common reasons for wheel speed sensor failure is contamination from dirt or debris. Accumulated dirt or grease can make it difficult for the sensor to read the rotating wheel’s speed. In some instances, metallic debris from a worn-out braking system can also interfere with the sensor’s magnetic field.
Electrical Issues
Bad wheel speed sensor symptoms include damaged wiring or connectors. When the wiring is pinched or damaged, the broken wires can interrupt the signal between the sensor and the ABS module. Corroded connectors may also lead to intermittent signals. If the module processing the sensor signal is not able to make sense of the changes in speed, there will be an electrical issue code. Internal short circuits within the sensor may also cause it to fail.
Physical Damage
Physical damage can also cause a wheel speed sensor to malfunction or fail. This can present in various ways, such as road debris or impact. Gravel or small rocks can hit the sensor when driving over harsh terrain, causing it to be damaged. Similarly, off-road driving through mud or snow can lead to the sensor being dislodged or broken. Finally, prolonged exposure to salt, humidity, and other corrosive elements can wear down the sensor, causing it to fail over time.
Wear and Tear
Regular use and constant exposure to harsh driving conditions, including gravel, thick mud, or snow, may also cause physical damage to the wheel speed sensor. The electronics, including its magnetic coil, can deteriorate over prolonged use in rough terrain. Similarly, the sensor housing and protective coverings of plastic tubing or rubber can become warped due to temperature changes. The sensor’s wires and connectors are also subject to movement as the wheels continuously turn. This type of repeated flexing may cause the wires to fray, leading to short circuits.
Faulty Installation or Manufacturing Defects
Improper installation of the sensor during assembly or when repairs are made may also cause misalignment, so it can not accurately measure wheel speed. This will also lead to inaccurate ABS control measures. During installation, overtightening may crack the housing, but loose mounting may cause excessive vibrations. Cracked housing allows debris to enter, causing damage as well.
Can You Drive with a Bad Wheel Speed Sensor?
The answer to whether you can drive with a bad wheel speed sensor is no. You should not drive with a faulty wheel speed sensor, even if it is technically possible. There are many inherent risks associated with operating a vehicle when this is the case, including unreliable ABS braking. The ABS might fail to engage, causing the potential for siding on wet roads. It could also deactivate modern Advanced Driver Assistance Systems like cruise control or automated emergency braking. This leaves the driver vulnerable as they cannot rely on the vehicle’s safety packages.
If you ignore these warnings, it could lead to other developing issues within the brain system, and they will not be immediately diagnosed. Rather, the problem should be addressed immediately. Once you see the ABS light flash and disappear, use an OBD-II scanner to confirm the fault. It will also show which sensor has failed. The process of replacing a problematic wheel sensor should be straightforward. Take the vehicle to the local shop or your trusted mechanic to diagnose and replace the sensor to avoid the potential safety risks discussed.
