The ABS consists of components such as the wheel
speed sensors, stoplight switch, hydraulic unit
assembly (integrated with ABS-ECU), ABS rotor,
ABS warning light relay and the ABS warning light. If
a problem occurs in the system, the malfunctioning
components can be identified and the trouble
symptoms will be memorized by the diagnostic
function.

In addition, reading of diagnostic trouble codes and
data list and actuator testing are possible by using
the Scan Tool.
If the ABS hydraulic unit is faulty, the ABS-ECU must
be replaced.
The ABS-ECU runs a self-check for 3 seconds upon
start-up (also ignition switch ON, engine stopped).
The ABS warning light, TCL warning light should be
illuminated during the self-check and turn off when
the self-check completes.

CONSTRUCTION DIAGRAM

System Check Sound
When starting the engine, 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.

ITEMS

SPECIFICATIONS

ABS type

4-sensor, 3-channel type

Speed sensor

Magnet coil type on 4-wheels

Front ABS rotor teeth

Rear ABS rotor teeth

AC003839

1. WHEEL SPEED SENSOR
2. STOPLIGHT SWITCH
3. HYDRAULIC UNIT (INTEGRATED

WITH ABS-ECU)

4. ABS WARNING LIGHT

5. DATA LINK CONNECTOR
6. ABS WARNING LIGHT RELAY
7. ABS ROTOR

ANTI-SKID BRAKING SYSTEM (ABS) DIAGNOSIS

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ANTI-LOCK BRAKING SYSTEM(ABS)

35B-3

•

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 tires 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
distance 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
normal characteristic because the ABS system
operation check is carried out when vehicle speed is
8 km/h (5 mph) or less.

AN TI-SK ID BR AK IN G SYSTEM (A B S) D IA G N O SIS

INTRODUCTION TO ANTI-LOCK BRAKE
SYSTEM DIAGNOSIS

M1352012500062

The anti-lock brake system (ABS) operates
differently from conventional brake systems. These
differences 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
characteristics 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
malfunction 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
specific 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 reset.

ABS DIAGNOSTIC TROUBLESHOOTING STRATEGY

M1352011100050

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.

5. If you can verify the condition but there are no

ABS DTCs, or the system cannot communicate
with the scan tool, check that the basic brake
system is operating properly.

•

If the basic brake system is not operating
properly, refer to the GROUP 35A, Basic Brake
System Diagnosis

P.35A-4

•

If the basic brake system is operating properly,
refer to

P.35B-22

6. If there is an ABS DTC, record the number of the

DTC, then erase the DTC from the memory using
the scan tool.

7. Recreate the ABS DTC set conditions to see if the

same ABS DTC will set again.

ANTI-SKID BRAKING SYSTEM (ABS) DIAGNOSIS

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ANTI-LOCK BRAKING SYSTEM(ABS)

35B-4

•

If the same ABS DTC sets again, perform the
diagnostic procedures for the DTC. Refer to

P.35B-8

•

If you cannot get the same ABS DTC to set
again, the malfunction is intermittent. Refer to
GROUP 00, How to use Troubleshooting/
Inspection Service Points

−

How to Cope with

Intermittent Malfunctions.

ABS TROUBLE CODE DIAGNOSIS

M1352011200068

Retrieving ABS Diagnostic Trouble Codes

Using Scan Tool MB991502

Required Special Tool:

•

MB991502: Scan Tool (MUT-II)

CAUTION

To prevent damage to scan tool MB991502, always turn the
ignition switch to the "LOOK" (OFF) position before
connecting or disconnecting the scan tool.
1. Connect scan tool MB991502 to the data link connector.

2. Turn the ignition switch to the "ON" position.

3. Use scan tool MB991502 to check for ABS diagnostic

trouble codes.

4. Turn the ignition switch to the "LOOK" (OFF) position.

5. Disconnect scan tool MB991502.

Using the ABS Warning Light and Special Tool MB991529

Required Special Tool:

•

MB991529: Diagnostic Trouble Code Check Harness

1. Use special tool MB991529 to ground number 1 terminal of

the data link connector.

2. Turn the ignition switch to the "ON" position.

3. Read out a diagnostic trouble code by observing how the

warning light flashes.

AC003081 AB

16 PIN

MB991502

AC003716 AB

DATA LINK
CONNECTOR

MB991529

AC003708 AB

ABS WARNING LIGHT

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