ABS Demonstrators

Find the ABS WSS (wheel speed sensor) pin-out connections to the ECU on the wiring diagram and the demonstrator. Record which ECU wires go to which WSS.

LF: ECU pin 2O and 2P
LR: ECU pin 2R and 2Q

RF: ECU pin 2N and 2M

RL: ECU pin 2S and 2T

By looking at the wiring diagram this type of speed sensor appears to be an Inductive type because it has only two wires.

The inductive sensor consists of a bar magnet with a soft magnetic pole pin supporting an induction coil with two connections. When a ring gear turns past this sensor, its tooth generates a voltage in the coil which is directly proportional to the periodic variation in the magnetic flux.

1. Shielded Cable
2. Magnet
3. Housing
4. Gear Box
5. Pole Piece
6. Coil
7. Air Gap
8. Missing tooth / Reference tooth


Locate an oscilloscope. Turn it on and set it up to be fully operational. What oscilloscope are you using?
Tektronix TDS 1002

Record a wave form wor each WSS.
Note readings are 5 volts per division and 100μ seconds per division for each.

FL


FR


RL


RR


As you can see from all the graphs they all look similar; however, FL & RR are approximately the same.
FR is higher than the rest and RL is lower.
There maybe several reasons for this, but in this case its most likely that the sensor's air gaps may all be slightly different to the others. e.g: since RL has the lowest readings, the gap maybe larger than the others, this causes the induced magnetic field to be slightly weaker than the readings from the others. Since FR has the highest, it's gap is likely to be smaller than the rest; making the induced magnetic field stronger, and thus getting a higher voltage reading.

With the WSS spinning, measure the AC volts with a multimeter and record here:
LF: 5.46v
LR: 4.21v
RL: 7.4v
RR: 6.23v

Can a multimeter be as accurate in finding problems with the WSS as an oscilloscope?
No, because the oscilloscope can show a visual of what is occuring in the circuit usually in real time.
Multimeters can only show up to a certain point what happens to currect, voltage etc. but if the signal is too fast, it wont be able to pick it up as well as an oscilloscope, therefore a multimeter may also display the average reading or an RMS reading.