Commander 4WD V8-4.7L VIN N (2006)
Parking Brake Warning Lamp: Description and Operation
BRAKE/PARK BRAKE INDICATOR
DESCRIPTION
A brake indicator is standard equipment on all instrument clusters. This indicator is located near the top of the cluster overlay, between the speedometer
and the tachometer. Illumination of this indicator may also be accompanied by the display of certain textual messages in the cluster dot matrix display.
The brake indicator consists of a stencil-like cutout of the word BRAKE and the International Control and Display Symbol icons for Brake Failure and
Parking Brake in the opaque layer of the instrument cluster overlay. The dark outer layer of the overlay prevents the indicator from being clearly visible
when it is not illuminated. A red Light Emitting Diode (LED) behind the cutout in the opaque layer of the overlay causes the indicator to appear in red
through the translucent outer layer of the overlay when it is illuminated from behind by the LED, which is soldered onto the instrument cluster electronic
circuit board.
The brake indicator is serviced as a unit with the instrument cluster.
OPERATION
The brake indicator gives an indication to the vehicle operator when the parking brake is applied, when there are certain brake hydraulic system
malfunctions as indicated by a low brake hydraulic fluid level condition, or when the brake fluid level switch is disconnected. The brake indicator can
also give an indication when certain faults are detected in the Antilock Brake System (ABS). This indicator is controlled by a transistor on the instrument
cluster circuit board based upon cluster programming, electronic messages received by the cluster from the Controller Antilock Brake (CAB) over the
Controller Area Network (CAN) data bus, and a hard wired input from the park brake switch.
The brake indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit, and that logic will only allow this
indicator to operate when the instrument cluster receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the LED
will always be off when the ignition switch is in any position except ON or START. The LED only illuminates when it is provided a path to ground by
the instrument cluster transistor. The instrument cluster will turn on the brake indicator for the following reasons:
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Bulb Test - Each time the ignition switch is turned to the ON position the brake indicator is illuminated by the instrument cluster for about three
seconds as a bulb test.
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Brake Lamp-On Message - Each time the cluster receives a lamp-on message from the CAB, the brake indicator will be illuminated. The CAB
can also send brake lamp-on messages as feedback during ABS diagnostic procedures. The indicator remains illuminated until the cluster receives
a lamp-off message from the CAB, or until the ignition switch is turned to the OFF position, whichever occurs first.
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Low Brake Fluid Textual Warning Message - When the CAB detects a low brake fluid level input from the brake fluid level switch, it will send
an electronic message requesting the cluster display a textual warning message. Each time the cluster receives a textual warning request message
from the CAB, a LOW BRAKE FLUID LEVEL textual message will appear within the instrument cluster dot matrix display to accompany brake
indicator illumination. This message indicates that the CAB has detected a low brake fluid level in the brake master cylinder.
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Park Brake Switch Input - Each time the cluster detects ground on the park brake switch sense circuit (park brake switch closed = park brake
applied or not fully released) while the ignition switch is in the ON position, the brake indicator flashes on and off. The indicator continues to flash
until the park brake switch sense input to the cluster is an open circuit (park brake switch open = park brake fully released), or until the ignition
switch is turned to the OFF position, whichever occurs first.
-
Antilock Brake System (ABS) Indicator Backup - If the instrument cluster detects a fault in the ABS indicator circuit it will send a message
indicating the fault to the Controller Antilock Brake (CAB), then flash the brake indicator on and off. The cluster will continue to flash the brake
indicator until the ABS indicator circuit fault is resolved, or until the ignition switch is turned to the OFF position, whichever occurs first.
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Actuator Test - Each time the instrument cluster is put through the actuator test, the brake indicator will be turned on, then off again during the
bulb check portion of the test to confirm the functionality of the LED and the cluster control circuitry.
The park brake switch on the park brake lever mechanism provides a hard wired ground input to the instrument cluster circuitry through the park brake
switch sense circuit whenever the park brake is applied or not fully released. The CAB continually monitors the ABS system circuits and sensors,
including the brake fluid level switch on the brake master cylinder reservoir, to decide whether the system is in good operating condition. The CAB then
sends the proper lamp-on or lamp-off messages to the instrument cluster. If the CAB sends a lamp-on message after the bulb test, it indicates that the
CAB has detected a brake hydraulic system malfunction and/or that the ABS system has become inoperative. The CAB will store a Diagnostic Trouble
Code (DTC) for any malfunction it detects.
The park brake switch input to the instrument cluster may be diagnosed using conventional diagnostic tools and methods. Refer to the appropriate wiring
information. For proper diagnosis of the brake fluid level switch, the ABS, the CAB, the CAN data bus, or the electronic message inputs to the
instrument cluster that control the brake indicator, a diagnostic scan tool is required.
