The ABS 8 ensures directional stability and control
during hard braking.
This ABS uses a 4-sensor 4-channel system that
controls all four wheels independently of each other.

• EBD (Electronic Brake-force Distribution system)

control provides the ideal braking force for the
rear wheels.

• Active wheel speed sensors have been installed,

that produce changes of current flow through the
wheel speed sensor circuit which is influenced by
the reluctor ring fitted to the wheel hub.

• Active wheel speed sensors have a constant

incoming power supply on one wire and return a
signal on the other wire

• The advantage of the active wheel speed sensor

is that there is always a signal until the wheel has
stopped. As the wheel speeds up or slows down,
the frequency will change where the amplitude of
the signal will remain constant.

• A Hall switch and magnet assembly is contained

within the sensor.

• As the tooth on the reluctor approaches the sen-

sor, the magnetic circuit is completed therefore
turning on the Hall switch. As the tooth departs
the sensor, the Hall switch will turn off.

• The output waveform displayed on the oscillo-

scope will be a square wave, (between signal
wire and ground).

• To shorten the harness wires and enhance data

transmission reliability, communication with other
ECU is performed over a CAN (Controller Area
Network).

NOTE: For further details on CAN communica-
tion, refer to GROUP 54C, CAN.

• Fail-safe function ensures that safety is main-

tained.

• Diagnostic function provides improved service-

ability.

NOTE: If the ABS-8 ECU or the active wheel
speed sensor are disconnected, or if the wiring is
an open/ short circuit, the ABS 8 ECU will shut
off power supply to the respective wheel speed
sensor. All other wheel speed sensors will oper-
ate normally. To restore the power supply, the
ignition switch must be cycled to the "OFF" posi-
tion then to the "ON" position again.

EBD CONTROL

In ABS, electronic control is used so the rear wheel
brake hydraulic pressure during braking is regulated
by rear wheel control solenoid valves in accordance
with the vehicle's rate of deceleration. The front and
rear wheel slippage are calculated from the signals
received from the various wheel sensors. EBD con-
trol provides a high level of control for both vehicle
braking force and vehicle stability. The system has
the following features:

• Because the system provides the optimum rear

wheel braking force regardless of vehicle load
and the condition of the road surface, the system
reduces the required pedal depression force, par-
ticularly when the vehicle is heavily loaded.

• Because the duty placed on the front brakes is

reduced, the increases in pad temperature can
be controlled during front brake application to
improve pad wear.

• Control valves such as the proportioning valve

are not required.

GENERAL DESCRIPTION

ANTI-LOCK BRAKING SYSTEM (ABS)

35B-3

CONSTRUCTION DIAGRAM

35DB031A

3, 7

35DB112A

NAME OF PART

NUMBER

OUTLINE OF FUNCTION

Sensor

Active wheel speed
sensor

Sends alternating voltage signals at frequencies which are
independant to the rotation speeds of each wheel to the
ABS-ECU.

Stoplight switch

Sends a signal to the ABS-ECU to indicate whether the
brake pedal is depressed or not.

Actuator Hydraulic unit

Drives the solenoid valves according to signals from the
ABS-ECU in order to control the brake hydraulic pressure
for each wheel.

ABS warning light

Illuminates in response to signals from the ABS-ECU
when a problem develops in the ABS system.

Brake warning light

Illuminates in response to signals from the ABS-ECU
when a problem develops in the EBD system.

Data link connector

Outputs the diagnostic trouble codes and allows
communication with the diagnostic tool.

ABS-ECU

Controls actuators (described above) based on the signals
coming from each sensor.

Controls the self-diagnosis and fail-safe functions.

Controls the diagnostic function (diagnostic tool
compatible).

ANTI-LOCK BRAKING SYSTEM (ABS) DIAGNOSIS

ANTI-LOCK BRAKING SYSTEM (ABS)

35B-4

SYSTEM CHECK SOUND

When the vehicle speed reaches 10 km/h after igni-
tion switch ON, a thudding sound can sometimes be
heard coming from the engine compartment. This is
a normal sound during the ABS self-check.

ABS OPERATION SOUNDS AND
SENSATIONS

During normal operation, the ABS makes several
sounds that may seem unusual at first:

• A whining sound is caused by the ABS hydraulic

unit motor.

• When pressure is applied to the brake pedal, the

pulsation of the pedal causes a scraping sound.

• When the brakes are applied firmly, the ABS

operates, rapidly applying and releasing the
brakes many times per second. This repeated
application and release of braking forces can
cause the suspension to make a thumping sound
and the tyres to squeak.

LONG STOPPING DISTANCES ON LOOSE
ROAD SURFACES

When braking on loose surfaces like snow-covered
or gravel roads, the stopping distance can be longer
for an ABS-equipped vehicle than the stopping dis-
tance for a vehicle with a conventional brake system.

SHOCK AT STARTING CHECK

Shock may be felt when the brake pedal is lightly
pressed while driving at a low speed. This is a nor-
mal characteristic because the ABS system opera-
tion check is carried out when vehicle speed is 8
km/h (5 mph) or less.

ANTI-LOCK BRAKING SYSTEM (ABS) DIAGNOSIS

INTRODUCTION TO ANTI-LOCK BRAKING SYSTEM DIAGNOSIS

M1352012500396

The anti-lock braking system (ABS) operates differ-
ently from conventional brake systems. These differ-
ences include sounds, sensations, and vehicle
performance that owners and service technicians
who are not familiar with ABS may not be used to.
Some operational characteristics may seem to be
malfunctions, but they are simply signs of normal
ABS operation. When diagnosing the ABS system,
keep these operational characteristics in mind.
Inform the owner of the kind of performance charac-
teristics to expect from an ABS-equipped vehicle.

ABS Diagnostic Trouble Code Detection
Conditions

ABS diagnostic trouble codes (ABS DTCs) are set
under different conditions, depending on the mal-
function detected. Most ABS DTCs will only be set
during vehicle operation. Some ABS DTCs will also
be set during the ABS self-check immediately after
the engine is started.
When you check if an ABS DTC will be displayed
again after the DTC has been erased, you should
duplicate the ABS DTC set conditions. Depending on
the detection timing and set conditions for the spe-
cific ABS DTC, you must either drive the vehicle or
turn the engine off and restart it. To set the proper
conditions for that DTC again, refer to "ABS DTC
SET CONDITIONS" for each ABS DTC that you are
trying to reset.

ABS DIAGNOSTIC TROUBLESHOOTING STRATEGY

M1352011100771

Use these steps to plan your diagnostic strategy. If
you follow them carefully, you will be sure that you
have exhausted most of the possible ways to find an
ABS fault.
1. Gather information about the problem from the

customer.

2. Verify that the condition described by the

customer exists.

3. Check the vehicle for any ABS DTC.

4. If you cannot verify the condition and there are no

ABS DTCs, the malfunction is intermittent. Refer
to GROUP 00, How to use
Troubleshooting/Inspection Service Points

− How

to Cope with Intermittent Malfunctions

P.00-14

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