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ANTI LOCK BRAKING SYSTEM (ABS)
22
6.2.3 TROUBLE SHOOTING AND
DIAGNOSIS
While the key is in IGN position, the ABS ECU
monitors the system for faults. Diagnostic information
and system function monitoring can be accessed by
connecting diagnostic tool to the vehicle diagnostic
connector.
After detecting a fault, the ABS ECU will select a
suitable default strategy which will retain, if possible,
some operational ABS capability. If ABS is not
active, conventional braking will remain available.
A. ROAD TEST
!! WARNING
It is essential that brake pedal travel is not
obstructed by items such as extra floor mats.
(a) While driving the vehicle with ABS
Observe the warning lights, check parking brake/fluid
warning light extinguishes after initial bulb check and
when the parking brake is released, indicating that
power assistance is available.
(b) Normal ABS brake operation
In road conditions where surface friction is sufficient
to slow or stop the vehicle without wheel lock, ABS
does not operate.
In an emergency braking situation, if one or more
wheels begin to slow rapidly in relation to vehicle
speed, ABS will detect wheel locking tendency and
will regulate brake pressure to maintain wheel
rotation.
(c) Brake application with partial failure:
!! WARNING
If a fault develops in the brake system it is essential
that it is investigated immediately.
i. TMC failure
If during braking, a drastically reduced resistance is
detected at the pedal and braking effectiveness is
very much reduced, failure of the non-powered
(master cylinder) portion of system is indicated. If
this occurs, do not pump the brake pedal. Push the
pedal through free movement to obtain braking effort
from the power circuit.
ii. Brake Booster failure.
When power assistance is not available, braking
effort is only available from the master cylinder In
this case the pedal travel will be or feel shorter as
there is no assistance and greater effort will be
required to stop the vehicle.
!! WARNING
Foot pressure on the pedal, using master cylinder
only, will not achieve the same degree of braking as
is available from power assistance.
ii. Insufficient fluid in TMC
If there is insufficient fluid in master cylinder to create
pressure, braking to all four wheels is retained and
ABS remains operative. The red warning light
(fluid
level indicator lamp)
will be illuminated if the level in
fluid reservoir is low
(due to leakage of fluid)
enough
to actuate fluid level switch.
!! WARNING
Longer pedal travel is required, but power assisted
braking is available at reduced efficiency.
B. TABLE OF ABS 8.1 - FALL-BACK LEVEL
ABS
FALLBACK
LEVEL
ABS Warning
Lamp
Brake Lamp
Status
System
System
active Lamp System
active
Lamp
System
active with
limitation
YES
OFF
NO
ON
System
active
YES
OFF
YES
OFF
Emergency -
EBD
NO
ON
YES
OFF
System
passive
NO
ON
NO
ON
NOTE
For brake bleeding procedure conventional/ using
diagnostic tool refer Brakes group.