Function and diagnostic role of wheel speed sensor
Wheel speed sensors are located near the hub or differential and are wont to determine the speed of the wheel around its circumference. they’re utilized in ABS, ASR and GPS systems.
The systems being combined, the anti-lock system makes available to the opposite systems, by means of knowledge transfers, the speeds which are recorded at the circumference of the wheel.
There are Hall effect sensors and inductive sensors. Before any check, it’s necessary to see the sort of sensor.
Functioning
- The rotation of the target disc mounted on the wheel hubs causes variations within the magnetic flux .
- The signals which are thus triggered are transmitted to the engine management computer then analyzed.
- The ABS computer determines the circumferential speed of the wheels. It thus determines the slip.
- These two parameters allow optimum braking action to be obtained without locking the wheels.
Effects of dysfunction
Consequences of a faulty wheel speed sensor:
- The ABS / ASR red light comes on.
- Recording of a fault code within the engine management computer.
- Locking the wheels when braking.
- Failure of other systems.
The causes of failure could also be due to:
- Internal short circuits.
- A disruption of the facility supply.
- A brief circuit within the electrical harness.
- Mechanical damage to the rotating target.
- Clogging of the sensor head.
- An excessive amount of play within the wheel bearing.
Diagnostics
- Read the fault code record
- Check the connection of the electrical wires of the sensor, the connector and people of the sensor to verify that they’re correctly connected, that they’re not broken which there’s no corrosion.
- confirm that the sensors aren’t dirty or damaged.
Checking the wheel speed sensor directly are often difficult if the precise sort of sensor isn’t known.
Before any verification, it should be known whether
it is an inductive or Hall effect sensor. it’s not always possible to differentiate them from each other , especially when the connection has three wires.
For all information,
refer to the precise instructions given by the manufacturer and to those within the Hella electronic catalog.
Do not use any ohmmeter until the sort / model is clearly determined, as this might destroy a Hall sensor.
If the sensor features a 2-pin connector, it’s basically an inductive sensor. during this case, it’s possible to work out the interior resistance, its insulation and therefore the signal.
To do this, you want to disconnect the sensor and check its internal resistance. If the worth of the interior resistance is between 800 and 1200 Ohm (depending on the reference value), the sensor is functioning correctly.
At 0 Ohm, there’s a brief circuit and at M Ohm (∞), there’s a current interruption.
The insulation is checked using the ohmmeter from the connection plug to the vehicle earth.
The resistance value must tend towards infinity. Checking with an oscilloscope should provides a sinusoidal waveform of sufficient power.
If it’s a Hall effect sensor, it’s only necessary to see the voltage of the square wave (which may be a function of the speed of rotation of the motor) and to see the availability voltage. for instance it again:
the use of an ohmmeter can destroy the Hall effect sensor.
Assembly advice:
Make sure there is a correct air gap between the target
