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.

Wiring Diagram Practice

Wheel Speed Sensors:
Front Right - Black & White
Front Left - Green & Red
Rear Left - Blue & Pink
Rear Right - Brown & Yellow




The reason for braided wire:
In the ABS System braided wire is used. This is to prevent external interference with the ABS signals. Being a safety feature it is extremely important that the signals are kept clear, as even the smallest of signal interferences at the wrong time could be fatal.

List of fuses used by the ABS circuit:
50A ABS, 10A gauge, 20A done, 15A stop, 15A ECU-16

Identify the Earths for the ABS control unit and ABS motor:
ON - A17-A A18-B
GND 10/GND 7

On the wiring diagram for the ABS actuator, identify which solenoids control which wheel cylinder. Note the wire colours and pin numbers.

Front Right Wheel - Pin Number: 2B
- Wire Colour: Red/white

Front Left Wheel - Pin Number: 3B
- Wire Colour: Blue/Red

Rear Left Wheel - Pin Number: 1B
- Wire Colour: Brown/White

Rear Right Wheel - Pin Number: 4B
- Wire Colour: Green/Black




Using the picture above as a guide, Identify what the Inlet and Outlet Solenoid Valves are doing at certain Braking conditions:

1. Under normal braking conditions the Inlet solenoid valve is Open, and the Outlet valve is Closed.
2. When the ABS is operating to reduce wheel brake pressure the Inlet valve is Closed and the Outlet valve is Open.
3. When the ABS is operating to hold brake pressure, the Inlet valve is Closed and Outlet valve is Closed.
4. When the ABS is operating to increase wheel brake pressure, the Inlet valve is Open, and Outlet valve is also Open.

The ABS Motor will operate in condition numbers 2, 3 and 4 above.


This graph shows a digital signal swithcing 5v every 2 seconds.


This graph shows an analogue signal with a frequency of 0.5 Hz and a maximum of +3v.

Think about ABS Repair!

Misconceptions, The ABS system should be simple and robust, with the Module/ECU/Controller almost never giving any trouble.

Possible reasons for damaging an ECU:
- Spiked by careless welding, i.e MIG welding without disconnecting the battery.
-Enclosure seal damaged and with obvious sign of water ingress
-Obvious signs of mechanical damage to the enclosure.

Often the ECU will be misdiagnosed as faulty, usually because the technician is inexperienced in fault finding.
Faults are much more likely to be with connectors or sensors.

-Be careful when working near the ECU. Make sure not to damage it in any way.
-When diagnosing, first check the easiest options, and work your way out to more difficult conclusions.
-Helps to volt drop ground connections & various sensors before resorting to replacing an ECU or different parts.

ABS Wiring Diagram:


1- Discs
2- Wheel Speed sensors
3- Gear/ tone ring
4- ABS module
5- Brake Master Cylinder
6- Brake Calipers
7- Brake booster