ABS Systems Workbook (4825)

Possible causes for damaging an ECU. True/False

• Spiked by careless welding, i.e MIG welding without disconnecting the battery. TRUE

• Enclosure seal damages and with obvious sign of water ingress.  TRUE

• Obvious signs of mechanical damage to the enclosure. TRUE

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

A visual check of the the wires, connections and sensors should be carried out first. Then check the ABS actuator/pump for any signs of damage. Then check the ABS fuses. Next check the ABS ECU connections and earth.

1   Brake disk
2   Sensor
3   Reluctor
4   ASB pump 
5   Master cylinder
6   Caliper
7   Brake booster

What is the reason for the braided wire on the ABS wheel sensor?

To stop voltage interference from other wires.

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

50 amp ABS pump main fuse
10 amp gauge warning light
20 amp dome
15 amp stop light
15 amp ECU-ig
FL main fuse 3.0 amp (wire)

Identify the earths for the ABS ECU and the ABS motor their wire colours and pin numbers.

ABS ECU earth pin (10,7) wire colour white/black

ABS motor earth pin (1) wire colour white/black

ASB actuator, identify which solenoids control which wheel cylinder then note the wire colours and pin numbers.

Front right wheel.  pin No. (2) wire colour red/white    pin No. (6) wire colour red/green

Front left wheel, pin No. (1) wire colour blue/red   pin No. (2) wire colour blue/white

Rear left wheel,  pin No. (10) wire colour brown/red   pin No. (11) wire colour brown white

Rear right wheel,  pin No. (14) wire colour green/black  pin No. (15) green/yellow

Using the picture below name the correct position of the inlet and outlet solenoids under normal braking?

 = Inlet valve Open - Outlet valve Closed

ABS operating to reduce wheel brake pressure?  = Inlet valve Closed - Outlet valve Open

ABS operating to hold brake pressure?   = Inlet valve closed - Outlet valve closed 

ABS operating to Increase wheel Brake pressure?   = Inlet valve closed - Outlet valve open

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

When the increasing or decreasing brake pressure.

Draw a DIGITAL SIGNAL that switches 5 volts every 2 seconds.

Draw a ANALOGUE SIGNAL with a frequency of 0.5 Hz and a maximum of +3 volts.

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 sensor :

Left front  ECU Pin # 4 and 5

Left rear  ECU Pin # 24 and 26

Right front  ECU Pin # 11 and 21

Right rear  ECU Pin # 7 and 9

By looking at the wiring, what type of sensor is this?  .... Inductive

Describe how it works.

Inductive or magnetic wheel speed sensors have two components one is a reluctor ring with iron teeth that spins at the same speed as the wheels. The other is a magnetic pickup which is placed with approx. 1mm gap from the toothed ring. As the teeth of the reluctor ring pass the magnetic pickup it changes reluctance depending on the distance of the gap. The closer the gap the stronger the magnetic field the bigger the gap the weaker the magnetic field this creates an AC voltage around the wires in the magnetic pickup and this voltage signal is sent to the ECU. This AC signal has low voltage and low frequency at low speeds and a high voltage and high frequency a higher speeds.

Use an oscilloscope to record a waveform from each wheel speed sensor note the voltage per division and time per division for each.

Right Front   5 volts / 500 ms

 Left Front   5 volt / 500us

Right Rear  5 volt / 500us

Are all the waveforms exactly the same? ...No

Discuss what are the differences and what caused these differences between the waveforms:

Left front and right rear were similar but right front shows a much exaggerated waveform this was because of a larger air gap between the toothed wheel and the magnetic pick-up. Below is a picture of a correct air gap between tooth wheel and pick-up.

Below is the air gap for right front this was the exaggerated waveform.

You can see it is quite a bit bigger than the first picture. This is a good example of how an oscilloscope can show a fault with a inductive wheel speed sensor.

ABS Relays

Power relay for ABS ECU - K38

ABS Pump relay - K100

ABS HCU relay - K38

ECU pin No. for the wire that brings power to the ABS ECU - 27

ECU pin No. for the wire that controls the relay for the ABS ECU - 1

Pin No. for wire that brings power to ABS pump - 30

Pin No. for the wire that controls the relay for the ABS pump - 86

ABS Pump Relay Waveform

Capture a waveform that shows both the control circuit change when it turns on the relay, and the power switching on to power the ABS pump.

Point (A) is the solenoid switched off. Point (B) pump relay switches on. Point (C) shows voltage pulled down pump is switched on. Point (C) is pump interferance.

Catch an oscilloscope patter when an ABS solenoid has actuated.