Test J: The Brake Warning Indicator Is Never On

PINPOINT TEST J: THE BRAKE WARNING INDICATOR IS NEVER ON

Normal Operation
The instrument cluster uses 3 basic messaged inputs to control the brake warning indicator. The first 2 are the parking brake warning indicator switch and brake fluid level switch. The third is for the electronic brake distribution (EBD), controlled by the anti-lock brake system (ABS). The parking brake warning indicator switch status is sent from the smart junction box (SJB) over the medium speed controller area network (MS-CAN) communication bus. The brake fluid level switch status is sent from the SJB (except Hybrid) over the MS-CAN or the ABS module (Hybrid) over the HS-CAN. The electronic brake distribution message is sent from the ABS module over the HS-CAN communication bus lines. The parking brake warning indicator switch is hardwired to the SJB through signal circuit CCB09 (GY/BU). The brake fluid level switch is hardwired to the SJB through signal circuit CMC19 (GY/VT).

The SJB provides a reference voltage to both the parking brake switch and the brake fluid level switch. When the parking brake is applied, the parking brake warning indicator switch closes to ground through circuit GD182 (BK/GY), providing a ground to the SJB and pulling signal circuit CCB09 (GY/BU) low. When a low brake fluid level condition exists, the low brake fluid level switch closes to ground through circuit GD120 (BK/GN), pulling signal circuit CMC19 (GY/VT) low. The SJB monitors the parking brake input and sends the instrument cluster a message to turn the brake warning indicator on when the parking brake is applied. The SJB (except Hybrid) or the ABS module (Hybrid) monitors the brake fluid level and sends the instrument cluster a message to turn on the brake warning indicator when a low brake fluid level condition exists. When the ABS module detects a base brake system concern or other ABS related concerns that affect the electronic brake distribution function, the ABS module sends a message to the instrument cluster to illuminate both the ABS warning indicator and the brake warning indicator.

This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- Brake fluid level switch (part of the brake fluid reservoir)
- Parking brake warning indicator switch
- SJB
- ABS module
- Instrument cluster

J1-J4:

J4-J7:

J7-J8:

J9-J11: