ANTI-LOCK BRAKING SYSTEM (ABS) DIAGNOSIS
TSB Revision
ANTI-LOCK BRAKING SYSTEM (ABS)
35B-3
System Check Sound
When starting the engine, a thudding sound can
sometimes be heard coming from the engine com-
partment. 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 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 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
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The anti-lock brake 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 reset.
TROUBLESHOOTING STRATEGY
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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.00-6
.
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.