Mazda Training manual — part 90

Dynamic Driving Safety Systems

ABS

Active Wheel Speed Sensor

•

The active wheel speed sensors are either hall element type or giant magneto resistor
type, i.e. the sensors need a power supply (provided by the CM) and output a
rectangular signal with the aid of an integrated circuit.

•

The height of the signal is not affected by the wheel speed. This means the active wheel
speed sensor can transmit a proper wheel speed signal even at very low speeds
(approx. 0.1 km/h).

•

The CM uses the number of pulses per second to calculate the wheel speed. The
vehicle speed is calculated by the CM based on the wheel speed of all wheels.

NOTE: An active wheel speed sensor must not be inspected using an ohmmeter.

NOTE: The difference between the High and Low signal can be as low as 0.2 Volt.

NOTE: Strong vibrations can demagentise permanent magnets. Hammer blows in the

vicinity of the magnetic layer on a wheel bearing (e.g. when replacing the bearing)
could permanently damage the magnetic layer, causing a faulty wheel speed signal.

L2003_02011

A

Detection principle

3

Magnetic rubber (magnetic encoder)

B

Output waveform

4

Semiconductor element

1

ABS wheel-speed sensor

5

Sensor output signal

2

Active drive circuit

6

Semiconductor element signal

Curriculum Training

02-19

ABS

Dynamic Driving Safety Systems

L2003_02054

1

Wheel speed sensor

2

ABS HU/CM

Diagnostics

•

The active wheel speed sensor can be checked by:

–

Reading out DTCs

–

Checking the voltage signal

–

Checking the air gap

–

Monitoring the corresponding PIDs (see below)

PID

Definition Unit/Condition

LF_WSPD

LF ABS wheel-speed sensor input

km/h, mph

LR_WSPD

LR ABS wheel-speed sensor input

km/h, mph

RF_WSPD

RF ABS wheel-speed sensor input

km/h, mph

RR_WSPD

RR ABS wheel-speed sensor input

km/h, mph

L2003_T02005

02-20 Curriculum

Training

Dynamic Driving Safety Systems

ABS

Brake Switch

•

The brake switch, which is actuated by the brake pedal, informs the ABS control module
when the brake pedal is pressed. This signal is necessary to recognize that the driver
wants to slow down the vehicle using the brake. The ABS will not start operating until a
corresponding signal from the brake switch is received.

•

The brake switch is a standard On/Off switch that is either hardwired to the ABS control
module or its information is forwarded via CAN (e.g. on Mazda6 F/L where it is
hardwired to the PCM and forwarded from there via HS-CAN to the ABS control
module).

NOTE: On some vehicles, if the brake switch has been removed it must be discarded, and a

new one must be installed (refer to the W/M).

L2003_02013

1

Brake pedal

3

Brake switch

2 Brake

switch

connector

Curriculum Training

02-21

ABS

Dynamic Driving Safety Systems

Diagnostics

•

The brake switch can be checked by:

–

Reading out DTCs

–

Checking the voltage signal

–

Measuring its resistance

–

Monitoring the corresponding PID (see below)

PID

Definition Unit/Condition

BOO_ABS

Brake pedal switch

ON/OFF

L2003_T02028

ABS Warning Light

•

The yellow ABS warning light is located in the IC. It illuminates after ignition on for a few
seconds to inform the driver that the warning light has no malfunction.

•

If it stays on or illuminates during driving, a malfunction has been detected. As long as
the warning light is illuminated the ABS control is switched off, but the standard brake
system is fully operational, if there is no other warning light illuminated. All current
Mazda vehicles feature a DTC memory function, which stores the malfunction in the
ABS control module.

•

If a temporary malfunction has been detected that does not exist any more, the failure
will be stored and the warning light will go off after switching the ignition off and on.

L2003_02014

1

IC

2

ABS warning light

02-22 Curriculum

Training