Wheel speed sensors have changed over the years, as have diagnostic aids. While oscilloscopes are great diagnostic tools, it's no longer common to see technicians drive them to diagnose problems with the wheel speed sensor in newer vehicles.
By Taylor Wolff
Wheel speed sensors have changed over the years, as have diagnostic aids. While oscilloscopes are great diagnostic tools, it's no longer common to see technicians drive them to diagnose problems with the wheel speed sensor in newer vehicles.
The most common type of wheel speed sensor seen today is magnetoresistive. These sensors are also called active wheel speed sensors because they require power to operate. The sensor works by detecting changes in the magnetic field of the toothed ring, commonly in the wheel hub, with a semiconductor and a magnetic resistive element inside the sensor.
When the wheel is spinning, it causes the multipolar rotor ring to generate an alternating magnetic field, which in turn causes the sensor to turn on and off its output, creating a signal that is used by the anti-lock brake module.
I used a 2020 Chevrolet Silverado to demonstrate a problem with the wheel speed sensor. I removed the rear sensor and contaminated it with metal shavings. This is not an uncommon problem of seeing in the field due to the sensor environment.
They are prone to accumulating brake dust and metal chips as the wheel bearings wear out. Metal chips interfere with the magnetic field which disrupts the sensors' ability to accurately detect it. The truck immediately responded with several warning messages and indicators on the dashboard display.
Next, I used General Motors' factory scan tool, GDS2, to view the sensor data. I compared the input of the left rear sensor (the failed sensor) with the right rear sensor.
As shown in the graphs, where the right wheel speed sensor works normally, the left sensor signal shows little fluctuation and almost never gives any signals.
This illustrates that diagnosing most modern wheel speed sensor problems can be as simple as a visual component and wiring check along with the use of factory scanning tool equipment.
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