3.1.1
PEDAL FEEL/VEHICLE
CHARACTERISTICS
There are several pedal feel/vehicle characteris-
tics that are considered normal for antilock braking
that may require further explanation.
When stopping conditions activate the antilock
brakes, the driver may feel some vibrations/
pulsations in the brake pedal and may hear the
solenoid valves clicking and the pump motor run-
ning. The vibrations/pulsations are caused by the
isolating, building and decaying of brake fluid pres-
sure within the brake lines. The ABS prevents
complete wheel lock-up, but some wheel slip is
required for the best braking performance. This slip
may result in some tire chirping, depending on the
road surface. This chirping should not be inter-
preted as total wheel lock-up. Total wheel lock-up
leaves black tire marks on dry pavement. Antilock
braking may leave some light marks.
At the end of an ABS stop, the ABS system may
not function below 5 Km/h (3 mph). There may be a
slight brake pedal drop anytime the ABS is deacti-
vated.
In case of braking on a bumpy surface, the ABS
module may detect wheel locking tendencies due to
wheel hop and cycle ABS. In that event the brake
pedal may pulsate with a perceived loss of deceler-
ation. ABS braking may also be activated at times
while on dry pavement with sand, gravel, or other
loose debris on the road.
It should be noted that the pulsating pedal feel
characteristic will not illuminate the brake warning
indicators or set a diagnostic trouble code that is
stored in the Controller Antilock Brake (CAB).
When investigating a hard pedal feel, inspect the
sensor and tone wheel teeth for chips/broken teeth,
damaged sensor pole tips, excessive runout of the
tone wheel, or excessive gap.
3.1.2
SYSTEM COMPONENTS
Antilock Brake System
•
controller antilock brake (CAB)
•
vacuum booster
•
master cylinder (w/center valves)
•
hydraulic control unit (HCU)
valve block assembly: 6 valve solenoids (3 inlet
valves, 3 outlet valves), 3
accumulators
•
pump/motor assembly: 1 motor
2 pumps
•
G (acceleration) switch
•
1 proportioning valve
•
4 wheel speed sensor/tone wheel assemblies
•
ABS warning indicator
•
fuses and wiring harness
•
fluid reservoir (integral part of master cylinder
assembly)
3.1.3
ABS AND BRAKE WARNING
INDICATORS
The amber ABS warning indicator is located in
the instrument cluster. It is used to inform the
driver that the antilock function has been turned off
due to a system malfunction. On a TJ model the
warning indicator is controlled by the CAB and the
ABS relay. The CAB controls the indicator by di-
rectly grounding the ABS relay control circuit. The
ABS relay grounds the indicator circuit when it is
de-energized.
The red brake warning indicator is located in the
instrument cluster. It can be activated by applica-
tion of the parking brake, low brake fluid level or by
turning the ignition switch to the start position.
3.1.4
CONTROLLER ANTILOCK BRAKE
(CAB)
The
controller
antilock
brake
(CAB)
is
a
microprocessor-based device that monitors wheel
speeds and controls the antilock functions.
The primary functions of the CAB are:
•
monitor wheel speeds
•
detect wheel locking tendencies
•
control fluid pressure modulation to the brakes
during antilock stop operation
•
monitor the system for proper operation
•
provide communication to the DRBIII
t
while in
diagnostic mode
•
control the ABS relay
•
store diagnostic information in non-volatile mem-
ory
The CAB continuously monitors the speed of each
wheel. When a wheel locking tendency is detected,
the CAB will command the appropriate valve in the
HCU to modulate brake fluid pressure to that
wheel. Brake pedal position is maintained during
an antilock stop by being a closed system with the
use of three accumulators. The CAB continues to
control pressure in individual hydraulic circuits
until a wheel locking tendency is no longer present.
The CAB turns on the pump/motor during an an-
tilock stop.
The antilock brake system is constantly moni-
tored by the CAB for proper operation. If the CAB
detects a system malfunction, it can disable the
antilock system and turn on the ABS warning
indicator. If the antilock function is disabled, the
system will revert to standard base brake system
operation.
2
GENERAL INFORMATION
Summary of Contents for Wrangler TJ 2003
Page 4: ...NOTES iv...
Page 13: ...7 0 DIAGNOSTIC INFORMATION AND PROCEDURES 9...
Page 52: ...NOTES 48...
Page 56: ...NOTES 52...
Page 61: ...C O N N E C T O R P I N O U T S 57 CONNECTOR PINOUTS...
Page 64: ...NOTES 60...
Page 66: ...10 2 AXLE LOCK S C H E M A T I C D I A G R A M S 62 SCHEMATIC DIAGRAMS...
