DaimlerChrysler LH New Yorker 1994, Электронное руководство по обслуживанию

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Store diagnostic information in non-volatile
memory.
The (CAB) continuously monitors the speed of each
wheel. When a wheel locking tendency is detected,
the (CAB) will command the appropriate valve to
modulate brake fluid pressure in its hydraulic circuit.
In order to increase pressure at the wheel brake
again, the inlet valve in the (HCU) is opened to the
wheel brake which causes the pedal to drop. During
an anti-lock stop, the brake pedal position is main-
tained within a controlled region by the Pedal Travel
Sensor (PTS) and the pump/motor. The PTS has
seven resistance steps. Once an anti-lock control cycle
has been initiated, the (CAB) will activate the
pump/motor when the PTS level increases one step.
The (CAB) will again turn off the pump/motor once
the original position is reached again. The (CAB)
continues to control pressure in individual hydraulic
circuits until a wheel locking tendency is no longer
present.
On traction control equipped vehicles ONLY, the
(CAB) is continuously monitoring wheel speed, it can
also detect wheel spin (traction loss) conditions. If the
(CAB) detects drive wheel spin and the brakes are not
applied it will enter the Traction Control mode. When
a wheel spin condition is detected the (CAB) will close
the normally open Traction Control Valves. When the
Traction Control valves are closed the master cylinder
primary and secondary chambers, and the rear brake
channels are isolated from the drive wheel brake chan-
nels. The pump motor is started to supply fluid
volume/pressure to the drive wheel brake channels.
The pump runs continuously during traction control
operation. The inlet and outlet valves are opened and
closed to modulate the hydraulic pressure in the ap-
propriate brake channel. By cycling the inlet and out-
let valves, the (CAB) can control wheel spin by apply-
ing the brakes on the wheel that has lost traction.
The Anti-Lock Brake and Traction Control Systems
are constantly monitored by the (CAB) for proper
operation. If the (CAB) detects a fault, it can disable
the Anti-Lock and Traction Control function and turn
on the warning lamps. If the Anti-Lock function is
disabled, the system will revert to standard base
brake system operation.
The (CAB) Inputs include the following:
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Four Wheel Speed Sensors
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Stop Lamp Switch
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Pedal Travel Sensor
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Ignition Switch
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Main Relay Voltage
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Pump/Motor Sensor Signal
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Diagnostic Communication (C2D) Fluid Level
Switch #2
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Traction Control Switch
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ABS Warning Lamp Voltage
The (CAB) Outputs include the following:
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Eight Valve/Solenoid Drivers (Ten with Traction
Control)
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Main Relay Actuation
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Pump/Motor Relay Actuation
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Anti-lock Light Actuation
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Brake Warning Light Actuation
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Traction Control Warning Lamp Actuation
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Traction Control Function Lamp Actuation
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Diagnostic Communication (C2D)
DIAGNOSTIC CONNECTOR
On the L.H. platform, the Teves Mark IV diagnos-
tic connector is located under the lower instrument
panel to the right side of the steering column. The
diagnostics connector is a blue 6 way connector see
(Fig. 7).
ANTI-LOCK SYSTEM RELAYS AND WARNING
LAMPS
SYSTEM RELAY
The System Relay (Fig. 8) is attached to the outside
of the Power Distribution Center. The System Relay
has two functions. First, when the relay is energized,
it supplies power to the solenoid valves in the Valve
Block Assembly and the pump/motor relay coil. Sec-
ond, when the relay is de-energized, it supplies a
ground to turn on the ANTI-LOCK warning light. The
System Relay is controlled by the (CAB). The (CAB)
energizes the System Relay when it receives an igni-
tion input signal.
PUMP/MOTOR RELAY
The Pump/Motor Relay (Fig. 8) supplies power to
the pump/motor. It is attached to the outside of the
Power Distribution Center (PDC). The relay coil is
powered by the System Relay and the coil ground is
controlled by the (CAB).
The Pump/Motor Relay is a special four terminal
relay and should not be replaced with a standard re-
Fig. 7 ABS Diagnostic Connector Location
ANTI-LOCK BRAKE SYSTEM 5 - 83