SENSOR-FRONT WHEEL SPEED
DESCRIPTION
The antilock brake system uses two-wire wheel speed sensors, known as active wheel speed sensors. The sensors
use an electronic principle known as magnetoresistive to help increase performance and durability. The sensors
convert wheel speed into a small digital signal. A Wheel Speed Sensor (WSS) is used at each wheel. A magnetic
pole encoder serves as the trigger mechanism for each sensor. At each wheel of the vehicle there is one wheel
speed sensor and one encoder.
A front wheel speed sensor (3) is attached to a mount-
ing boss on each front knuckle (4). The encoder is an
integral part of the hub and bearing.
WSS air gaps are not adjustable.
OPERATION
The ABM sends 12 volts to power an Integrated Circuit (IC) in the sensor. The IC supplies a constant 7 mA power
supply to the ABM. The relationship of the magnetic pole encoder to the permanent magnet in the sensor, signals
the IC to enable a second 7 mA power supply. The output of the sensor, sent to the ABM, is a DC voltage signal
with changing voltage and current levels. The ground for the IC and the current sense circuit is provided by the
ABM.
When a pole is properly aligned with the sensor, the voltage signal is approximately 0.8 volts and a constant 7 mA
current is sent to the ABM. As the magnetic pole encoder rotates, the encoder shifts the magnetic field and the IC
enables a second 7 mA current source. The ABM senses a voltage signal of approximately 1.6 volts and 14 mA.
The ABM measures the amperage of the digital signal for each wheel. The resulting signal is interpreted by the ABM
as the wheel speed.
REMOVAL
NOTE: Before proceeding, (Refer to 5 - BRAKES - WARNING) (Refer to 5 - BRAKES - CAUTION).
PM
BRAKES - ABS SERVICE INFORMATION
5 - 309