Dodge 2000 DURANGO Service Manual page 188

5 - 34 BRAKES
DESCRIPTION AND OPERATION (Continued)
OPERATION
SYSTEM SELF-TEST
When the ignition switch is turned-on the micro-
processor RAM and ROM are tested. If an error
occurs during the test, a DTC will be set into the
RAM memory. However it is possible the DTC will
not be stored in memory if the error has occurred in
the RAM module were the DTC's are stored. Also it
is possible a DTC may not be stored if the error has
occurred in the ROM which signals the RAM to store
the DTC.
CAB INPUTS
The CAB continuously monitors the speed of the
differential ring gear by monitoring signals generated
by the rear wheel speed sensor. The CAB determines
a wheel locking tendency when it recognizes the ring
gear is decelerating too rapidly. The CAB monitors
the following inputs to determine when a wheel lock-
ing tendency may exists:
• Rear Wheel Speed Sensor
• Brake Lamp Switch
• Brake Warning Lamp Switch
• Reset Switch
• 4WD Switch (If equipped)
CAB OUTPUTS
The CAB controls the following outputs for antilock
braking and brake warning information:
• RWAL Valve
• ABS Warning Lamp
• Brake Warning Lamp
RWAL VALVE
DESCRIPTION
The valve is located on the drivers side inner
fender under the hood. The valve modulates hydrau-
lic pressure to the rear brakes during an RWAL stop.
OPERATION
If the CAB senses that rear wheel speed decelera-
tion is excessive, it will energize an isolation solenoid
by providing battery voltage to the solenoid. This
prevents a further increase of driver induced brake
pressure to the rear wheels. If this initial action is
not enough to prevent rear wheel lock-up, the CAB
will momentarily energize a dump solenoid (the CAB
energizes the dump solenoid by providing battery
voltage to the solenoid). This opens the dump valve
to vent a small amount of isolated rear brake pres-
sure to an accumulator. The action of fluid moving to
the accumulator reduces the isolated brake pressure
at the wheel cylinders. The dump (pressure venting)
cycle is limited to very short time periods (millisec-
onds). The CAB will pulse the dump valve until rear
wheel deceleration matches the desired slip rate pro-
grammed into the CAB. The system will switch to
normal braking once wheel locking tendencies are no
longer present.
A predetermined maximum number of consecutive
dump cycles can be performed during any RWAL
stop. If excessive dump cycles occur, a DTC will be
set and stored in the CAB memory. If during a RWAL
stop, the driver releases the brake pedal, the reset
switch contacts will open. This signal to the CAB is
an indication that pressure has equalized across the
RWAL valve. The CAB will then reset the dump cycle
counter in anticipation of the next RWAL stop. Addi-
tionally, any fluid stored in the accumulator will
force its way past the dump valve, back into the
hydraulic circuit and return to the master cylinder.
A fuse internal to the CAB, provides a fail-safe
device which prevents unwanted control over the iso-
lation and dump solenoids. The fuse is in series with
the isolation and dump solenoids output circuits. If
the internal fuse is open, the CAB cannot provide
voltage to energize either solenoid and RWAL stops
are prevented. If the fuse is open, the braking system
will operate normally but without antilock control
over rear brake pressure.
REAR WHEEL SPEED SENSOR AND EXCITER
RING
DESCRIPTION
The rear Wheel Speed Sensor (WSS) is mounted in
the rear differential housing (Fig. 2).
Fig. 2 Rear Wheel Speed Sensor Location
1 – DIFFERENTIAL HOUSING
2 – WHEEL SPEED SENSOR
The exciter ring is press fitted onto the differential
carrier next to the final drive ring gear (Fig. 3). For
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