DaimlerChrysler LH New Yorker 1994, Электронное руководство по обслуживанию

Страница: 171 / 1203

BRAKE WARNING LAMP
The red BRAKE Warning Lamp is located in the
Instrument Panel. It can be activated in several
ways. Application of the parking brake or a low fluid
signal from the fluid level switch located in the mas-
ter cylinder reservoir will cause the lamp to come on.
The (CAB) will also activate the brake warning lamp
if there is a fault in the ABS system, and the amber
anti-lock lamp fails to operate. Both the red and the
amber lamps will flash when the system is placed in
the diagnostic mode with the DRB II. ABS operation
is disabled while in the diagnostics mode.
TRACTION CONTROL FUNCTION LAMP
The Green Traction Control Function Lamp is lo-
cated in the message center. It is used to inform the
driver that the system has entered the traction con-
trol mode. The lamp is controlled by the (CAB). The
(CAB) turns on the lamp by directly grounding the
circuit.
TRACTION CONTROL WARNING LAMP
The Amber Traction Control Warning Lamp is also
located in the message center. It is used to inform the
driver that the Traction Control function has been
turned off by the (CAB). This lamp will also come on
if the traction control switch is in the off position and
the ignition is on.
NORMAL OPERATION OF WARNING LAMP
With the ignition in the Crank position, the Red
Brake Warning Lamp will turn on as a bulb check.
The Amber Anti-Lock Warning Lamp and the Trac-
tion Control Lamps will stay on for 1-2 seconds then
turn off, ounce verification of the self diagnosis is
completed.
ANTI-LOCK BRAKE SYSTEM COMPONENTS
The following is a detailed description of the Anti-
Lock Brake System components. For information on
servicing the Four Wheel Disk Brake System, see the
standard Brake section of this Service Manual.
HYDRAULIC CONTROL UNIT (HCU)
WARNING: ONLY THE FOLLOWING COMPONENTS
OF THE (HCU) (FIG. 1) ARE SERVICEABLE. THE
BRAKE
FLUID RESERVOIR, PROPORTIONING
VALVES AND MOUNTING ISOLATORS. THE RE-
MAINING COMPONENTS OF THE (HCU ARE NOT
SERVICEABLE ITEMS AND NO ATTEMPT IN ANY
WAY SHOULD BE MADE TO REMOVE OR SERVICE
ANY OTHER PARTS OF THE (HCU).
The (HCU) (Fig. 1 and 2) is located in the engine
compartment on the left frame rail forward of the
master cylinder and is covered by a heat shield. The
Hydraulic Control Unit (HCU) contains the valve
block assembly, the pump/motor assembly, and a fluid
reservoir with a fluid level switch.
There are two Hydraulic Control Units. One is
used for ABS only. The other is used for ABS and
Traction Control combined. Each has a different part
number. If the wrong H.C.U. is installed, the system
operation will be disabled and a fault code will be
stored.
VALVE BLOCK ASSEMBLY
The valve block assembly (Fig. 2) contains eight/ten
valve/solenoids; four inlet valves and four outlet
valves. (2 isolation valves for traction control pres-
sure switch only.) The inlet valves are spring loaded
in the open position and the outlet valves are spring
loaded in the closed position. During an anti-lock
stop these valves are cycled to maintain the proper
slip ratio for each channel. If a wheel locks, the inlet
valve is closed to prevent any further pressure in-
crease. Then the outlet valve is opened to release the
pressure back to the reservoir until the wheel is no
longer slipping. Once the wheel is no longer slipping
the outlet valve is closed and the inlet valve is
opened to reapply pressure. If the wheel is decelerat-
ing within its predetermined limits (proper slip ra-
tio), both valves will close to hold the pressure con-
stant. During the stop, the build pressure is initially
supplied by the master cylinder. When the build
pressure is reapplied, fluid comes from the master
cylinder which causes the brake pedal to drop. The
pedal continues to drop until the Pedal Travel Sensor
signals the (CAB) to turn on the pump/motor. The
pump/motor then pumps fluid from the reservoir into
the brake system. The master cylinder pistons and
brake pedal are then moved back until the Pedal
Travel Sensor signals the (CAB) to turn off the
pump/motor.
On vehicles equipped with traction control, the
valve block assembly also contains the two Traction
Fig. 1 Hydraulic Control Unit (HCU) Mounting
Location
5 - 80 ANTI-LOCK BRAKE SYSTEM