Chrysler Concorde 2004 Service Manual page 1528

5 - 62 BRAKES - ANTILOCK BRAKE SYSTEM
BRAKES - ANTILOCK BRAKE SYSTEM (Continued)
DESCRIPTION - ELECTRONIC VARIABLE
BRAKE PROPORTIONING
Vehicles equipped with ABS use electronic variable
brake proportioning (EVBP) to balance front-to-rear
braking. The EVBP is used in place of a rear propor-
tioning valve. The EVBP system uses the ABS sys-
tem to control the slip of the rear wheels in partial
braking range. The braking force of the rear wheels
is controlled electronically by using the inlet and out-
let valves located in the integrated control unit
(ICU).
EVBP activation is invisible to the customer since
there is no pump motor noise or brake pedal feed-
back.
DESCRIPTION - TRACTION CONTROL
Traction control reduces wheel slip and maintains
traction at the driving wheels at speeds below 56
km/h (35 mph) when road surfaces are wet or snow
covered. The traction control system reduces wheel
slip by braking the wheel that is losing traction.
OPERATION
OPERATION - ANTILOCK BRAKES
There are a few performance characteristics of the
Mark 20e Antilock Brake System that may at first
seem abnormal, but in fact are normal. These char-
acteristics are described below.
NORMAL BRAKING
Under normal braking conditions, the ABS func-
tions the same as a standard base brake system with
a diagonally split master cylinder and conventional
vacuum assist.
ABS BRAKING
ABS operation is available at all vehicle speeds
above 5–8 km/h (3–5 mph). If a wheel locking ten-
dency is detected during a brake application, the
brake system enters the ABS mode. During ABS
braking, hydraulic pressure in the four wheel circuits
is modulated to prevent any wheel from locking.
Each wheel circuit is designed with a set of electric
solenoids to allow modulation and each wheel
receives its own separate electrical signal. Wheel
lockup may be perceived at the very end of an ABS
stop and is considered normal.
During an ABS stop, the brakes hydraulic system
is still diagonally split. However, the brake system
pressure is further split into four control channels.
During antilock operation of the vehicle's brake sys-
tem, the front wheels are controlled independently
and are on two separate control channels, and the
rear wheels are controlled together for better vehicle
stability.
The system can build and release pressure at each
wheel, depending on signals generated by the wheel
speed sensors (WSS) at each wheel and received at
the controller antilock brake (CAB).
NOISE AND BRAKE PEDAL FEEL
During ABS braking, some brake pedal movement
may be felt. In addition, ABS braking will create
ticking, popping, or groaning noises heard by the
driver. This is normal and is due to pressurized fluid
being transferred between the master cylinder and
the brakes. If ABS operation occurs during hard
braking, some pulsation may be felt in the vehicle
body due to fore and aft movement of the suspension
as brake pressures are modulated.
At the end of an ABS stop, ABS is turned off when
the vehicle is slowed to a speed of 5–7 km/h (3–4
mph). There may be a slight brake pedal drop any-
time that the ABS is deactivated, such as at the end
of the stop when the vehicle speed is less than 5
km/h (3 mph) or during an ABS stop where ABS is
no longer required. These conditions exist when a
vehicle is being stopped on a road surface with
patches of ice, loose gravel, or sand on it. Also, stop-
ping a vehicle on a bumpy road surface activates
ABS because of the wheel hop caused by the bumps.
TIRE NOISE AND MARKS
Although the ABS system prevents complete wheel
lockup, some wheel slip is desired in order to achieve
optimum braking performance. Wheel slip is defined
as follows: 0 percent slip means the wheel is rolling
freely and 100 percent slip means the wheel is fully
locked. During brake pressure modulation, wheel slip
is allowed to reach up to 25–30 percent. This means
that the wheel rolling velocity is 25–30 percent less
than that of a free rolling wheel at a given vehicle
speed. This slip may result in some tire chirping,
depending on the road surface. This sound should not
be interpreted as total wheel lockup.
Complete wheel lockup normally leaves black tire
marks on dry pavement. The ABS will not leave dark
black tire marks since the wheel never reaches a
fully locked condition. However, tire marks may be
noticeable as light patched marks.
START-UP CYCLE
When the ignition is turned on, a popping sound
and a slight brake pedal movement may be noticed.
The ABS warning indicator lamp will also be on for
up to 5 seconds after the ignition is turned on. These
conditions occur as part of ABS self-diagnosis check.
The popping sound is a result of brief activation of
the solenoids in the integrated control unit.
LH