But, the square wave signal does not need to be processed by the BCM; it is a direct input. An active wheel speed sensor creates a digital signal. On a typical passenger vehicle weighing around 3,400 pounds, each pair of front-wheel bearings, as well as the rear-wheel or axle bearings, support around 850 pounds, depending on the weight balance and driveline configuration. The advantages of the active speed sensors are their ability to read more accurately at slow speeds than the passive speed sensors. On the test drive, take a corner to see how the speed changes between the inside wheel and outside wheel. At this location, the wheel speed sensors are more accurate and often more protected from the elements. The amplitude of the signal for an inductive sensor will change as the speed of the reluctor increases. A magneto resistive sensor has a sensing element that contains an output module that is mounted on a substrate and magnetic material. Another product type that can sense reverse rotation is also available upon request. ��������@���F�2���Ҳ@� The time base is set to allow all of the signals per revolution to appear on the display. Codes for erratic performance can be caused by the physical relationship between the wheel bearing encoder ring and the wheel speed sensor. 0000018996 00000 n In the past decade, wheel speed sensors have been moving from differentials, axles and knuckles to inside or on the wheel bearing or hub unit. The ABS module supplies voltage to the wheel speed sensor. (Tip: Check a known-good wheel speed sensor on the opposite side of the vehicle to get the exact value.) The high signal must cross 1.29V and the low signal must cross 0.97V to low. One of which is used as a voltage power supply from the ABS control module. This is due to the air gap tolerances between the encoder ring and sensor. The sensor produces a square wave signal with a high signal of 1.93 volts, and a low signal of 0.64 volts. They don’t have to self-generate the needed voltage by the spinning action of the wheel. of play is allowed for most sealed wheel bearing and hub assemblies. If it’s a 6,000-pound SUV, each bearing might carry about 1,500 pounds. With a vehicle on a lift, you can observe wheel speed sensor data as you spin a wheel. 0000002332 00000 n The average wheel bearing job may require a scan tool, scope or meter to verify the operation of the sensor. The angular position sensor is a sensor for electric brake pedals. This load is concentrated on the relatively small bearing surfaces. Nowadays, bearing play is best measured by placing a dial indicator against the hub and turning the wheel. Next, examine the integrity of the wiring. When the untrained technician does not see power at the sensor, he may think the module is defective and replace the module. 0000017692 00000 n 0000016326 00000 n At this location, the wheel speed sensors are more accurate and often more protected from the elements. The diagnosis of a trouble code or problem condition requires an investment in information and tools. #active safety Bias voltage tests also work to detect opens in the circuit. %PDF-1.4 %���� More stories from Andrew Markel can be found here. An active wheel speed sensor takes voltage from the ABS module (ranging from 8 to 12 volts) and changes the voltage signal by only 0.6 to 1.2 volts. The wheel speed sensors can detect the direction of rotation of the reluctor ring and zero speed. ABS warning light (and other associated warning lights) illumination. Missing peaks and valleys can indicate damage to the encoder ring. The inertial measurement unit offers a six-dimensional measurement of accelerations and angular rates in three axes. Also, measure the output of the voltage or the presence of a bias voltage to confirm the operation of the module. 0000001880 00000 n Once the bearing has worn through the treated layer, rapid and catastrophic wear occurs to the softer metal below. The material loss of the races and rolling element creates play and noise. H�lUkPW�{@h��!�""��R�8�(���JTPP���q���+$�-+���M��` Sensors provide the inputs the Powertrain Control Module (PCM) needs to make critical control decisions. If the circuit is compromised by an open or short, the increased or decreased resistance causes the voltage to drop or exceed specifications. Firing the “parts cannon” at an active ABS wheel speed sensor code often results in misdiagnosis and an unhappy customer. It may start with the wheel bearing hub unit or wheel speed sensor. This will also affect the oscilloscope display. Trouble Codes C1141 through C1144 can be caused by a missing tooth and can be verified with a scope. This is why if a wheel speed sensor is disconnected, it will cut power and set a code. The circuit is exposed to the changing magnetic field of the rotating encoder, which is either a multipole or a steel wheel. All rights reserved. The output is how the ABS control module sees the wheel speed sensors. When the bearing play is great enough, the seal attached to the inner race becomes dislodged from the groove in the outer race. An active wheel speed sensor takes voltage from the ABS module (ranging from 8 to 12 volts) and changes the voltage signal by only 0.6 to 1.2 volts. The scan tool is the most efficient tool for diagnosing ABS sensor problems, and if you are servicing three and four year-old vehicles, your shop cannot function well without it. This type of fatigue failure is called “spalling.” The damage causes the metal to come off in flakes. 0000010049 00000 n 0000008269 00000 n The module protects itself by sending out a low-voltage signal for a millisecond when it is first turned on and performs a self-check. From the heat-treated wheel bearing races to the microcircuit inside the ABS module that processes the signal, you need to understand the mechanical and electrical operation of this foundation technology that is critical to ABS, stability control and ADAS. This type of digital wheel speed sensor uses a hall effect or a variable reluctance signal with a square wave pattern. For its wheel-speed sensors, Bosch offers different standard sensor heads suitable for various customer applications. If you see sudden drops in speed, it’s a sign that the air gap between the encoder ring and sensor has changed due to play inside the bearing. If the readings from the bias voltage tests are correct, the module provides voltage to the circuit for operation.