ABS Off-Car

Anti-lock Braking Systems Lab Workbook (4825)

Off-car Exercises Think about ABS Repair: Misconceptions. The ABS system should be simple and robust, with the Module/ECU/Controller almost never giving any trouble. Below are some possible causes for damaging an ECU.

• Spiked by careless welding, i.e. MIG welding without disconnecting the battery. True
• Enclosure seal damaged and with obvious sign of water ingress. True
• Obvious sign s of mechanical damage to the enclosure. True

Often the ECU will be misdiagnosed as faulty, usually because the technician is inexperienced in faultfinding.

• Faults are much more likely to be with connections or sensors. True

Discuss how these ECU issues should be incorporated into diagnostic practices to test an ABS system:

Whilst checking for connection and/or sensor faults check the ECU housing for physical damage also


Lets review the ABS system to remind ourselves what components are included and how they should work.

Name the Numbered parts in the diagram.

1. Disc Brake
2. Wheel Speed Sensor
3. Toothed Rotor
4. Electronic Control Unit
5. Brake Master Cylinder
6. Brake Caliper
7. Brake Booster


Wiring Diagram Practice

There are a number of components in the ABS Systems that are also used for fuel injection. These are mostly speed sensors e.g. wheel speed and engine speed.

Using the wiring diagram in the workshop manuals identify the wheel speed sensors and list their wire colours for each sensor.

• Front Right: White Black
• Front Left: Green Red
• Rear Left: Blue Pink
• Rear Right: Yellow Brown

On the ABS wheel sensor what is the reason for the braided wire?

• To provide protection and noise reduction.

Identify and list all the fuses that are used by the ABS Circuit.

• F14 Fuse Box, 10A Gauge, 20A Dome, 15A Stop, FL Main 3.0W and 15A ECU-IG.

Identify the earths for the ABS control unit and ABS motor the wire colours and what pin numbers.

• BI, BJ and BL (all white and black) for ECU are pins 10 and 7.
• EA and EB (White and Black for both) for motor pin 6 on relay and pin 1 on actuator.

On the Wiring Diagram for the ABS Actuator, identify which solenoids control which wheel cylinder. Then note the wire colours and pin numbers.

• Front Right Wheel: Pins 2B/6B, RedWhite/RedGreen
• Front Left Wheel: Pins 3B/7B, BlueRed/BlueWhite
• Rear Left Wheel: Pins 4B/8B, GreenBlack/GreenYellow
• Rear Right Wheel: Pins 1B/5B, BrownWhite/BrownRed

Which of the following gives the correct condition of the inlet and outlet solenoids valves under normal braking?

• A: Inlet valve open , Outlet valve open

Which of the following gives the correct condition of the inlet and outlet solenoids valves when the ABS is operating to reduce wheel brake pressure?

• C: Inlet valve closed , Outlet valve open

Which of the following gives the correct condition of the inlet and outlet solenoids valves when the ABS is operating to hold wheel brake pressure?

• D: Inlet valve closed , Outlet valve closed

Which of the following gives the correct condition of the inlet and outlet solenoids valves when the ABS is operating to increase wheel brake pressure?

• B: Inlet valve open , Outlet valve closed

In the four cases above state when the ABS motor will be working.

• Whilst Holding, Reducing and Increasing Wheel Brake Pressure.

There are three main types of wheel speed sensors on modern vehicles. One sends an analogue signal using an inductive pick-up, the others send a digital signal using either a hall effect or magneto-resistant encoder.

On the graph below draw a digital signal that switches 5V every 2s.
Mark V and t scales on the graph that will show the signal well.








On the graph below draw an analogue signal with a frequency of 0.5Hz and a maximum of +3 volts. Mark V and t scales on the graph that will show the signal well.