ABS Demonstrators

Locate the wiring diagram for your demonstrator vechicle. 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:

This demonstration is done on Mazda 323 JM BA

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, what type of speed sensor is this?

It is a magnetic sensor, therefore its a four channel speed sensor which has individual sensor for each wheel.

Describe how it works:

It works according to the wheel sensor which approximately 1mm above the sensor rotor therefore when wheel rotates the pulse ring rotates as well. When each pulse ring passes under the sensor, a small voltage pulse is present in the sensor. Finally the pulse sents the input signals 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 Oscillioscope QC1992.

Record a waveform for each wheel speed sensor in the boxes below. Note voltage per division and time per division for each. Please don't keep the Abs units on very long because it drains the battaries.

Which wheel is this? Left Front 2O / 2P

Which wheel is this? Left Rear 2R / 2Q

Which wheel is this? Right Front 2N / 2M

Which wheel is this? Right Rear 2S / 2T

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

No, because the front and rear sensors provides different waveforms. The front right and front left sensors shows the amplitude reading of 0.6V whereas the rear right and the rear left reading were 0.4v but the frequency for both sensors are 0.38ms. Both the rotors have 44teeth but while checking resistance the front wheel is 0.430K and the rear wheel has 0.890K.

With the wheel speed sensors spinning, measure AC volts with a multimeter and record here:

Left Front - 3.17V

Left Rear - 2.68V

Right Front - 4.22V

Right Rear - 2.85V

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

No

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

The oscilloscope gives the visual reading of what is captured by the sensor, for example if there is a chip, dent, scratch or any type of damage on the the rotor teeth then the oscilloscope will detect and display broken lines or distorting lines and it will indicate the fault.