Mazda Training manual - part 90

 

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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 

 

Detection principle 

Magnetic rubber (magnetic encoder) 

Output waveform 

Semiconductor element 

ABS wheel-speed sensor 

Sensor output signal 

Active drive circuit 

Semiconductor element signal 

 
 

Curriculum Training 

02-19 

ABS 

Dynamic Driving Safety Systems 

 

 

L2003_02054 

 

Wheel speed sensor 

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 

 

Brake pedal 

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 

 

IC 

ABS warning light 

 
 

02-22 Curriculum 

Training 

 

 

 

 

 

 

 

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