Off Car
Possible problems for damaging an ECU:
- Spiked by careless MIG welding True
- Enclosure seal damaged and with obvious sign of water ingress. True
- Obvious signs of mechanical damage to the enclosure True
Sometime the ECU is misdiagnosed as faulty as 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.
Fill in the blanks,
1. Brake disc
2. Wheel speed sensor
3. Rotor
4. A.B.S module
5. Master cylinder
6. Caliper
7. Booster
Wiring Diagram Practice
Front Right +Black -White
Front Left +Red -Green
Rear Right +Brown -Yellow
Rear Left +Pink -Blue
The reason the A.B.S wheel sensor wire is braded as it helps to resist interference from other signals. This works by the braded wires inducing back into itself as it wraps around itself.
The A.B.S uses 6 fuses.
FL MAIN 3W
Fuse box, A.B.S 50A
Gauge 10A
DONE 20A
STOP 15A
ECU-16 15A
The earth, wire colours and pin outs for the A.B.S control unit and A.B.S motor:
The A.B.S Control unit earth colours are: White-Black.
Pin out: 10B-BI and 7B-BJ
The A.B.S motor earth colours are: White-Black.
Pin out: 1A-EA
Right front wheel: SFRA, Red-White +2B -6B. SFRR, Red-Green +6B -5B
Left front wheel: SFLA, Blue-Red +3B -1A. SFLR, Blue-White +7B -2A
Right rear wheel:SRRA, Green-Black, +4B -14A. SRRR, Green-Yellow +8B -14A
Left rear wheel: SRLA. Brown-White +1B -12B. SRLR, +Brown -Red, +5B
Under normal braking the inlet valve is open and the outlet valve is closed.
When A.B.S is operating the inlet valve is closed and the outlet valve is open.
When the A.B.S is operating to hold brake pressure the inlet and the outlet valves are closed.
The inlet valve would have to open and the outlet stay closed if you are to increase the brake the pressure while the A.B.S is working.
The motor will work to relieve pressure as well as increase pressure, so in the 2nd and 4th case above the motor would be functioning.
Key= Voltage on the left side
Time in sec along the bottom.
This is the digital wave form of a hall effect or magnetic resistant wheel sensor.
Key= Voltage on the left
Time in sec along the bottom
This is an analogue signal of an inductive type wheel sensor.
Using the formula time=1/F gave me basis of this graph.
A.B.S Demonstrators
These are inductive type wheel sensors. As the rotor tooth aproaches the pick up the voltage becomes more positive until it peaks when the tooth and pick up are at their closests. This is when the magnetic field is at its strongest. When the tooth starts to break away the voltage becomes more negative (as the magnetic field has been collapsed) until the next tooth comes around.
I used the oscilliscope Tektonic TDS 1002 to get these patterns
FL ECU pin# 20 and 2P
FR ECU pin#2N and 2M
LR ECU pin#2R and 2Q
RR ECU pin# 2S and 2T
Not all these waveforms are the same. The waveforms can be varied by different problems such as: an airgap could be to big, which would give a low voltage.
The magnet might have magnetic dust on it which would give a distorted reading.
Also you may have the wrong sized wheels on the car which would effect the wheel speed reading as a larger wheel would spin slower, to a smaller wheel that could be on the front.
The AC volt readings for each wheel are:
FL 3.2V
FR 4.2V
LR 2.7V
RR 2.9V
A multimeter cannot be as accurate as an oscilliscope, as an oscilliscope will show you on a screen exactly what the voltage is doing. The multimeter would only give you a reading which is obviously not as good.
A.B.S Relays
pg14 in book
1. Ignition switch
2.ABS motor relay
3.Fail safe relay
4.1H
5.2J
6.R/Y wire from ABS Relay.
7.2H
The top circuit is the control circuit as it receives the 12v to the windings the magnetic field starts to build up and switches the relay. As this switches the power circuit switches on to give 12v power. The contol circuit contact bounces which is where the control circuit gets the small 12v back and the power circuit loses its voltage for a split second.
ABS self test.
The light stays on till the motor starts. The light is on till the fail safe relay switches the ABS motor relay. At the same time the light goes off and the motor starts as the ABS relay turns on.
Create a fault.
With pressure being applied to the brakes by the pedal and more pressure applied to one wheel. As one wheel is braking harder than the other, the ABS actuates the solenoids to relieve pressure on the one wheel that has to much pressure allowing that wheel to catch up in speed.
The pin# and name of the solenoid oscilliscope pattern is: FL/1B
By connecting the positive to 1B and negative to earth you can get this pattern.
(have lost pic)
On Car
I have identified the;
Wheel speed sensor
ABS control uni
ABS modulator
ABS pump motor
Parking brake switch
Brake master cylinder
Brake fluid level switch
RPM sensor
Foot brake switch
Brake booster
Main ABS control unit fuse
This car has an inductive pick up wheel speed sensors.
You can tell this by the signal output being analogue.
Air Gap
FR0.7mm The sensor is clean but has a slightly bigger air gap, but just within specification.
FL0.55mm The sensor is clean and within specs.
Using the scan tool.
By spinning the wheel manually we were able to test the inductive pick up. The voltage was low as we cannot spin the wheel as fast as it can be driven. The frequency was also low for the same reason. The data here shows us that all solenoids are in the off position. Which means that the ABS is not being activated.
The results when turned on were;
ABS valve control relay ON
ABS warning lamp status ON
Battery positive voltage 12.63V
LF ABS in valve OFF
RR ABS out valve OFF
Hydraulic pump motor OFF
Brake warning lamp state ON
Brake switch in OFF
If none of the solenoids would turn on in Rex's car then he would be stuck in 4th gear, as this is the gear with all solenoids off. I think this is unusual as I don't think that the car would be able to limp home in 4th gear especially if it had to stop and take off again. Most cars all off gear would be 2nd or maybe 3rd.
