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 mounting 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).
1. Open the hood.
2. Disconnect the wheel speed sensor cable connector (2) from the wiring harness connector (3) on top of the frame rail (1) to the inside of the strut tower.
3. Raise and support the vehicle. (Refer to LUBRICATION & MAINTENANCE/HOISTING - STANDARD PROCEDURE)
4. Remove the grommet (1) from the hole in the body (7) and pull the wheel speed sensor cable out of the hole.
5. Remove the speed sensor cable routing clip (2) from the outside frame rail (6).
6. Remove the screw fastening the cable routing clamp (3) to the outside frame rail (6).
7. Remove the screw (1) securing the wheel speed sensor routing bracket (2) to the brake flex hose bracket (5).
8. Remove the mounting screw (2) fastening the wheel speed sensor head (3) to the knuckle (4). Pull the sensor head out of the knuckle.
NOTE: In the following step, the routing clip can be easily removed without damaging it by rotating it (with entire sensor) counterclockwise.
9. Remove the routing clip (1) securing wheel speed sensor cable to the knuckle (4). Remove the sensor from the vehicle.
INSTALLATION
CAUTION: Failure to install speed sensor cables properly may result in contact with moving parts or an over extension of cables causing an open circuit. Be sure that cables are installed, routed, and clipped properly.
1. Install the wheel speed sensor head (3) into the knuckle (4). Install the mounting screw (2) and tighten it to 12 N·m (106 in. lbs.).
2. Install the routing clip (1) securing the wheel speed sensor cable to the knuckle (4).
3. Position the wheel speed sensor routing bracket (2) on the brake flex hose bracket (5) and install the mounting screw (1). Tighten the mounting screw to 18 N·m (13 ft. lbs.).
4. Position the wheel speed sensor cable routing clamp (4) on the outside frame rail (6) and install the mounting screw (3). Tighten the mounting screw to 18 N·m (13 ft. lbs.).
5. Install the speed sensor cable routing clip (2) on the outside frame rail (6).
6. Insert the wheel speed sensor cable through the hole in the body (7) and install the grommet (1) in the hole.
7. Lower the vehicle.
8. Connect the wheel speed sensor cable connector (2) to the wiring harness connector (3) on top of the frame rail (1).
9. Perform the Diagnostic Verification Test and clear any faults. (Refer to 5 - BRAKES - STANDARD PROCEDURE)