Antilock Braking Systems Lab Workbook

firstly i was asked to find out about what could damage an ecu.

if you dont disconnect the battery when welding you can get a spike which could damage the ecu.
if the enclosure seal is damaged the ecu could get water damage.
damaging the ecu could wreck the inside components.
most common faults are just loose connections or faulty sensors.


the next task i had to label the components of the braking system:

1 = brake rotor
2 = speed sensor
3 = tooth wheel
4 = modulator
5 = master cylinder
6 = caliper
7 = brake booster



i was then asked to find the wheel speed sensors on the wiring diagrams below and list the wire colours of each sensor:

right front =  - white/ + black
front left =  - pink/ + blue
rear left =  - green/ + red
rear right =  - brown/ + yellow

the ABS wheel speed sensor has braded wire to stop frequency.

the fuses that are used by the ABS circuit are:
ABS fuse box, fusable link main, gauge, dome, stop, ecu

using the wiring diagram i was asked to find the earths for the ABS control unit and the ABS motor and their wire colours:

pin 10/ block B = W-B
pin 7/ block B = W-B


i was then asked to identify the solenoids to control each wheel cylinder and note the wire colours and pin numbers.

front right wheel = 2B/ 6B     red-white/ red-green
front left wheel = 3B/ 7B     blue-red/ blue-white
rear left wheel = 1B/ 5B     brown-white/ brown-red
rear right wheel = 4B/ 8B     green-black/ green-yellow


using the diagram below i was asked to say if the inlet and outlet solenoids were open or closed:

under normal braking:
inlet valve open and outlet valve closed

ABS operating to reduce wheel brake pressure:
inlet valve closed and outlet valve open

ABS is operating to hold brake pressure:
inlet valve closed and outlet valve closed

ABS is operating to increase wheel brake pressure:
inlet valve open and outlet valve closed

the motor pumps fluid in and in some cases the pump sucks fluid out aswell



below is a digital signal of a wheel speed sensor that switches 5 volts every 2 seconds:

http://ttec4825rex.blogspot.com/2010_10_01_archive.html

below is a analogue signal with a frequency of 0.5Hz and a maximum of +3 volts:

http://ttec4825rex.blogspot.com/2010_10_01_archive.html

ABS DEMONSTRATORS

on the wiring diagram below, i was asked to find the ABS sensor pin out connections to the ecu and record the which ecu wires go to which wheel speed sensors:

left front = ecu pin #4 and 5
left rear =  ecu pin #7 and 9
right front = ecu pin #11 and 21
right rear = ecu pin#24 and 26

this was a magnetic inductive type of speed sensor.
this has a magnetic pick up sensor with a cog that spins around. Each time a tooth passes by the sensor it creates a voltage, this charges up the windings on the sensor side.

below is a some waveforms of the the wheel speed sensors, i used a "tektronic TDS 1001B" oscilloscope.


right front:

left front:

right rear:

left rear:

i then measured the AC voltage with the wheel speed sensor spinning:

left front = 3.59V
left rear = 3.21V
right front = 3.00V
right rear = 3.62V

a multimeter cant give as good as a reading as an oscilloscope can because a oscilloscope gives an actual waveform and you can see what the voltage is doing.


ABS RELAYS

ABS ECU relay = K39
ABS pump relay = K100
ABS HCU solenoids = Y22 (hydrolic modulator)

power to ABS ECU = 26 A
control wire for ABS ECU = 1 B
power to ABS pump = 8 E
Control wire for ABS pump = 2 H


below is a relay waveform that shows both the control circuit change when it turns the relay and the power switching on to power something in the ABS system:

http://amirs4825.blogspot.com/2010/11/abs-relays.html

the bottom waveform is the control circuit and the top is the switching circuit.
the point between A and B is when the switch is on and running 12V.
C is when the control circuit is collapsing.
D is when the switch is about to turn on again and E is a slight oscillation.

below is a waveform  that shows the control circuit change when it turns on the relay and thepower switching on to power the ABS pump.

the top waveform is the switch, this is earth triggered and shows that when the key is on, the waveform drops strait down and when the key is turned back off, the waveform goes back up to its original state.
the bottom waveform is the pump, when the key is earth triggered, the pump starts to work, then when the switch is off, the pump winds down and goes back to its original state.

when the key is turned on, the ABS system begins to self test, this checks all of the components of the system except for the wheel speed sensor that can not be checked unless the vehicle is moving. this is because the wheels need to be moving to send a signal output.

i created a fault in my system by slowing down the wheel, this makes the system think that i am braking fast and am going to lock up the wheels, brake pedal then started pushing back up against my hand and the inlet solenoid for that wheel closed and the outlet valve opened to relieve pressure from the brakes.