Test M: The Brake Warning Indicator Is Always On

PINPOINT TEST M: THE BRAKE WARNING INDICATOR IS ALWAYS ON

M1-M5:

M6-M10:

M10-M11:

M12-M14:

Normal Operation
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.

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.

If the parking brake or brake fluid level status message is missing for less than 5 seconds, the brake warning remains in the last indication mode (on or off). If the parking brake or brake fluid level status message is missing for more than 5 seconds, the instrument cluster sets DTC U0140 in continuous memory and defaults the brake warning indicator on. If the instrument cluster looses communication with the ABS module or the ABS module is disconnected, the instrument cluster sets DTC U0121 in continuous memory and defaults the brake warning indicator on.

DTC B2479 - is an on-demand DTC that sets if the SJB detects a short to ground on the parking brake input circuit, CLS05 (BU/GY) during a self-test.

DTC C1125 - is a continuous and on-demand DTC that sets if the SJB detects an open or short to ground on the brake fluid level switch input, circuit CMC19 (YE/GY). If the brake fluid level switch is disconnected, the instrument cluster sets DTC C1125 and defaults the brake warning indicator on.

NOTE:
- If DTC U0121 is set in the instrument cluster, the ABS warning indicator will also be illuminated.
- If DTC U0140 is set in the instrument cluster, other observable symptoms may also be present such as tire pressure monitoring system (TPMS) warning indicator, backlighting and door ajar indication.
- If the brake system experiences an EBD failure, both the brake warning indicator and the ABS warning indicator illuminate.

Possible Causes
- Circuitry
- Parking brake switch
- Brake fluid level switch
- SJB
- Instrument cluster