Commander 2WD V8-4.7L (2008)
Brake Warning Indicator: Description and Operation
Brake/Park Brake Indicator
Description
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 reconfigurable 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
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:
-
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.
-
Brake Indicator Lamp-On Message - Each time the cluster receives an electronic brake indicator lamp-ON message from the CAB, the brake
indicator will be illuminated. The CAB may also send 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.
-
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 textual warning request message requesting the cluster display a textual warning message. Each time the cluster receives this
message from the CAB, a LOW BRAKE FLUID LEVEL textual message will appear within the cluster reconfigurable dot matrix display to
