ABS Demonstrators

Here are the ABS wheel speed sensor ECU pinouts :

Left front ..... ECU pin # 2O and 2P
Left rear ...... ECU pin # 2R and 2Q
right front ... ECU pin # 2N and 2M
Right rear ... ECU pin # 2S and 2T

By looking at the wiring diagram we can idenitfy the INDUCTIVE wheel speed sensors.
Because Hall effect or optical types use 3 wires but inductive or magnetic type use only 2 .

As the teeth approaches the sensor due to the magnetic field being crossed gets more opposite and is at the maximum when the teeth is at the closest point to the sensor ... as the teeth starts moving away from the sensor the magnetic field that crosses the sensor slowly disappears and the voltage becomes more negative until the magnetic field is so far that dosnt effect the sesnor at all ...as the speed of the ring teeth increases so does the voltage and frequency, this repeats as the next teeth approaches and the cycle continues. this kind of sensor creates AC waveform .
optical and hall effect type create a digital signal . some magnito resistor sensors can also create a digital signal.

We were using TDS1002 techtonic oscilloscope for the next excercise .

Front Left.

Front Right.

Rear left.

Rear right.

All the waveforms are not exactly the same due to the difference of the gap between each ring tooth and sensors on each wheel and because they all have different gaps.

These are the wheel speed sensor spinning and their measured AC Voltage with a multi-meter .

Left front: 5.46 Volts

Left rear: 4.21 Volts

Right front: 7.4 Volts

Right rear: 6.23 Volts

A multimeter is not as an accurate tool for finding problems on a wheel speed sensors . An oscilloscope is a very good tool for this task . A multimeter can not show us what exactly is happening to the live data we getting and can only give us the calculated root mean square RMS and unfortunatly can not show us what actualy is going on ... different voltages from different wheel sensors but at the same speed can also be caused by different gap sizes between tooth ring and sensors, magnetic dust on the sensor e.g. from driving on sand or wrong size wheels can also effect the voltage as a bigger wheel would rotate slower ...