Normal Operation

WARNING: This page is about a different car, the 2007 Lincoln MKX and 2007 Ford Edge. However, it is still accessible from the selected car via links, so may be relevant.

The brake warning indicator alerts the driver if any of the following brake system conditions are present: the parking brake is set, the brake fluid level is low or the ABS module detects a electronic brake distribution (EBD) failure. If the brake system experiences an EBD failure, both the brake warning indicator and the ABS warning indicator illuminate.

When the parking brake is applied, the parking brake switch grounds circuit CLS05 (BU/GY) to the smart junction box (SJB). The SJB detects the ground signal and sends the instrument cluster a message over the medium speed controller area network (MS-CAN) to illuminate the brake warning indicator.

The SJB provides a reference voltage to the brake fluid level switch on input circuit CMC19 (GY/VT) with the signal return on circuit RMC19 (YE/GY). The brake fluid level switch is grounded through circuit GD120 (BK/GN). When the brake fluid level is low, the brake fluid level switch closes the input signal circuit to ground, pulling the reference low. When the SJB detects the reference voltage pulled low, the SJB sends a message to the instrument cluster over the MS-CAN to turn on the brake warning indicator.

When an EBD failure is detected, the ABS module sends a signal to the instrument cluster over the communication network to illuminate the brake system warning indicator.

Possible Causes

Circuitry
Parking brake switch
Brake fluid level switch
SJB
Instrument cluster