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5-54 Hydraulic Brakes
Power brake booster vacuum .hose routing on the
5.7L VB series engine.
Brake Warning System Description
Brake
222997
The. brake system uses a single red BRAKE warning
lamp located in the instrument cluster. When the
ignition switch is in the ST ART position, the BRAKE
warning lamp should turn on. When the ignition switch
is in the RUN position, the BRAKE warning lamp
should turn off.
The following conditions activate the BRAKE
warning lamp:
• The parking brake is applied. The lamp should be
on when the parking brake is applied and the
ignition switch is ON.
• The brake pressure differential warning switch
detects a failure. Refer to Electrical Diagnosis
for diagnosis.
• The BRAKE warning lamp remains on while
cranking the engine. This indicates that the circuit
is operating properly.
Antilock
The Antilock Brake System (ABS) uses
three indicator lamps:
• The red BRAKE warning lamp
• An amber ABS INOP indicator lamp
• An amber LOW TRAC indicator lamp
The lamps operate normally under the following
conditions:
• When the ignition is turned to the RUN position,
prior to starting the engine, the amber ABS
INOP indicator lamp should turn on and the red
BRAKE warning lamp should flash.
• While the engine is cranked, the red BRAKE
warning lamp and the amber ABS INOP indicator
lamp should turn on. The amber LOW TRAC
indicator lamp may turn on and off.
Brakes
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When the engine is started, .the amber ABS INOP
lamp and the red BRAKE lamp should turn off.
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The amber LOW TRAC indicator lamp may turn
on and off.
The operation of the three lamps is an important part
of the Antilock Brake System (ABS) diagnosis. A
malfunction is present if the warning/indicator lamps
turn on while driving the vehicle. If the warning
lamps do not turn on under normal conditions as
described above, service the lamps as soon as
possible. For further information regarding the
operation ofthe warning/indicator lamps for the
Antilock Brake System (ABS), refer to Antilock Brakes ..
Brake Warning System Circuit Description
Circuit Operation
The brake warning indicator on the instrument cluster
illuminates under the following conditions:
• The instrument cluster bulb test .is occurring.
• The park brake is set.
• The master cylinder brake fluid level is low.
• The electronic brake control module sends a
Class 2 message to the instrument cluster.
These conditions are explained in detail below. In all
cases positive voltage is applied to the brake
warning indicator through circuit 39.
Instrument Cluster Bulb Test
When the ignition switch is turned to the RUN position,
the instrument cluster performs an internal bulb test
on the brake warning indicator. The indicator
illuminates for approximately 3 seconds and then
turns off.
Park Brake
The park brake switch closes when the park brake is
set. On Domestic and Gulf States vehicles, ground
is applied through circuit 1134, the DRL module
and circuit 33 to the instrument cluster. The brake
indicator illuminates. On Europe and Japan vehicles,
ground is applied through circuit 33 to the cluster.
Brake Fluid level
When the brake fluid level in the master cylinder is
low, the brake fluid level indicator sensor closes.
Ground is applied through the sensor and circuit 33 to
the instrument cluster. The brake indicator illuminates.
EBCM Class 2
The brake indicator is also controlled by the ABS
system through the class 2 serial data line. The
electronic brake control module (EBCM) sends a
class 2 message to illuminate the brake indicator. The
indicator warns the customer that a problem exists
in the ABS system. Refer to ABS brakes for further
information.
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