1. ABS Sensors Their Operation and Waveform Produced
Motor Vehicle Level 3
Resource 4
ABS Sensors Their Operation and Waveform Produced 1

2. Aims Motor Vehicle Level 3 Resource 4
ABS Sensors Their Operation and Waveform Produced
Aims
To recognize various sensors used within ABS systems and their role within the system 2

3. Objectives By the end of this session you will be able to:
Motor Vehicle Level 3 Resource 4
ABS Sensors Their Operation and Waveform Produced
Objectives
By the end of this session you will be able to:
Identify various sensors including hall, and be able to describe passive and inductive sensors and their operation
Recognize the role of the speed sensor and it's location
Recognize and comment on the waveforms produced.
Comment briefly on how to maintain the sensor, and identify possible faults. 3

4. Types of sensor : Active Sensor
Motor Vehicle Level 3 Resource 4
ABS Sensors Their Operation and Waveform Produced
Types of sensor : Active Sensor
Example:-Magnetised pick up (crankshaft sensor, ABS sensor)
Voltage signal produced is sent to the input of the ECU for analysation.
The ECU will covert this Analogue signal to Digital signal which the ECU can read.
The ECU will now react (alter the brake pressure depending on this voltage signal. 4

5. Types of sensor : Passive Sensor (three wire)
Motor Vehicle Level 3 Resource 4
ABS Sensors Their Operation and Waveform Produced
Types of sensor : Passive Sensor (three wire)
Three wire device
Supply voltage for the sensor is supplied via the ECU
The internal resistance alters with a change in environment these are usually used to sense movement (i.e. throttle position)
This is measured by the ECU and the ECU will alter accordingly 5

6. Types of sensor : Passive Sensor (two wire device)
Motor Vehicle Level 3 Resource 4
ABS Sensors Their Operation and Waveform Produced
Types of sensor : Passive Sensor (two wire device)
Similar to a three wire device, the sensors internal resistance will alter with a change in environment rather than change in movement (i.e. engine coolant)
ECU Supplies voltage to the sensor,
The ECU will measure the change in internal resistance and react accordingly. 6

7. ABS Sensors Motor Vehicle Level 3 Resource 4
ABS Sensors Their Operation and Waveform Produced
ABS Sensors
Of course, ABS will use an active sensor
Why do you think that is?
Could it use a passive sensor? 7

8. ABS Wheel Speed Sensor Motor Vehicle Level 3 Resource 4
ABS Sensors Their Operation and Waveform Produced
ABS Wheel Speed Sensor
Wheel Speed Sensors are mounted at each wheel and sends a rotation signal to the ECU
Wheel speed sensors can be mounted to the steering knuckle or to the axle carrier 8

9. ABS Wheel Speed Sensor Motor Vehicle Level 3 Resource 4
ABS Sensors Their Operation and Waveform Produced
ABS Wheel Speed Sensor 9

10. ABS Wheel Speed Sensor Motor Vehicle Level 3 Resource 4
ABS Sensors Their Operation and Waveform Produced
ABS Wheel Speed Sensor
As the teeth of the sensor rotor pass the iron core, magnetism will cut through the coil windings Inducing a voltage
When the tooth is centered to the iron core 0v is produced
As the tooth moves away from the iron core, the magnetic field expands producing a negative voltage
As the wheel rotates faster the voltage and frequency increase (indicating to the ECU that the vehicle is travelling faster) 10

11. Waveform produced Motor Vehicle Level 3 Resource 4
ABS Sensors Their Operation and Waveform Produced
Waveform produced
In order to diagnose a fault within an ABS system waveforms are useful in order to determine system performance, and will also give hints as to the problem. 11

12. Waveform produced Motor Vehicle Level 3 Resource 4
ABS Sensors Their Operation and Waveform Produced
Waveform produced
The following images where taking using a diagnostic tool called a Picoscope
These show two wheel speed sensors being monitored, one has a fault...is it the red trace or the blue trace? 12

13. Waveform produced Motor Vehicle Level 3 Resource 4
ABS Sensors Their Operation and Waveform Produced
Waveform produced 13

14. Waveform produced Motor Vehicle Level 3 Resource 4
ABS Sensors Their Operation and Waveform Produced
Waveform produced
this small capture taken from the waveform produced indicates a fault compared with the blue trace
The fact the we have a waveform at all indicates that the sensor is producing a signal.
Therefore, we can diagnose that the rotor wheel has failed. 14

15. Waveform produced Motor Vehicle Level 3 Resource 4
ABS Sensors Their Operation and Waveform Produced
Waveform produced
This vehicle measures rear wheel speed via a driveshaft, upon inspection, we can see that the teeth have been damaged, furthermore, we can see this corresponds to our waveform produced.
Another factor that could have produced a similar waveform could have been distance from the sensor to the rotor or contamination of the sensor. 15

16. Waveform produced Motor Vehicle Level 3 Resource 4
ABS Sensors Their Operation and Waveform Produced
Waveform produced
In order to check the voltage is correct to the sensor
Ensure that your multimeter is correct and on the correct function (direct v)
Measure between the terminals as shown (always refer to manufactures guidelines)
The voltage should be between 10v-14v 16

17. Probing a Sensor Motor Vehicle Level 3 Resource 4 Continuity check
ABS Sensors Their Operation and Waveform Produced
Probing a Sensor
Continuity check
Is done to check that there is no faults in the wiring harness between the ECU, the Actuator and the ABS relays and possibly to the sensors.
Refer to manufactures guidelines
From the signal contact in the terminal blocks check the resistance between each components.
The resistance should be around 4-6Ώ 17

18. Summary Motor Vehicle Level 3 Resource 4 Have We:-
ABS Sensors Their Operation and Waveform Produced
Summary
Have We:-
Identified various sensors including hall, and be able to describe passive and inductive sensors and their operation
Recognized the role of the speed sensor and it's location
Recognized and commented on the waveforms produced.
Commented briefly on how to maintain the sensor, and identify possible faults. 18