ABS Demonstrators

Locate the wiring diagram for your demonstrator vehicle. Find the ABS wheel speed sensor pin-out connections to the ECU on the wiring diagram and the demonstrator. Record which ECU wires go to which wheel speed sensors:

• Left Front ECU Pin# 4 and 5 B19
• Left Rear ECU Pin# 7 and 9 B21
• Right Front ECU Pin# 11 and 21 B20
• Right Rear ECU Pin# 24 and 26 B22

By looking at the wiring diagram, what type of speed sensor is this?

Magnetic i.e. Pulse Generator, Inductive.

Describe how it works:

The toothed rotor spins in accordance to wheel speed.
The wheel speed sensor picks up the distance in the teeth of the rotor.
The fluctuating distance changes the reluctance which causes the magnetic field of the wires inside the sensor to generate an AC voltage.
This signal is then sent to the ECU.

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

Digitech Dual-Channel Oscilloscope 20 MHz QC1922.

Record a waveform for each wheel speed sensor in the boxes below. Note voltage per division and time per division for each.





Are all the waveforms exactly the same? No. Discuss what are the differences, and what can cause these differences between the waveworms:

Just mild fluctuations in voltage


With the wheels speed sensors spinning, measure AC volts with a multi-meter and record here:

Left Front 3.5V Resistance=1.4K ohms

Left Rear 2.5V Resistance=1.43K ohms

Right Rear 5.2V Resistance=1.6K ohms

Right Front 4.4V Resistance=1.62K ohms.

Can a multi-meter be as accurate in finding problems with the wheel speed sensors as an oscilloscope? No.

Discuss what the oscilloscope could find that the multi-meter can not find and why:

The oscilloscope would be more accurate in picking up things like damaged toothed rotor or or bad signal