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