Pinpoint Test N: The Brake Warning Indicator is Always On
Instrumentation, Message Center and Warning Chimes
Pinpoint Test N: The Brake Warning Indicator is Always On
Refer to Wiring Diagram Set 60, Instrument Cluster for schematic and connector information. Diagrams By Number
Normal Operation
The Instrument Cluster (IC) 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 ABS. The parking brake warning indicator switch and the brake fluid level switch status are sent from the Smart Junction Box (SJB) over the Medium Speed Controller Area Network (MS-CAN) communication bus. The EBD message is sent from the ABS module over the MS-CAN communication bus lines. The parking brake warning indicator switch is hardwired to the SJB through circuit CMC25 (WH/VT). The brake fluid level switch is hardwired to the SJB through signal circuit CMC19 (GY/VT) and return circuit RMC19 (YE/GY).
The SJB provides a reference voltage to both the parking brake warning indicator switch and the brake fluid level switch. When the parking brake is applied, the parking brake warning indicator switch closes to ground through circuit GD120 (BK/GN), providing a ground to the SJB and pulling signal circuit CMC25 (WH/VT) low. When a low brake fluid level condition or an open in the signal or return circuits 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 and the brake fluid level inputs sending the IC a message to turn the brake warning indicator on when the parking brake is applied or when the brake fluid level is low. When the ABS module detects a base brake system concern or other ABS-related concerns that affect the EBD function, the ABS module sends a message to the IC to illuminate both the ABS warning indicator and the brake warning indicator.
If the brake fluid level or parking brake status messages are missing for less than 5 seconds, the IC defaults the brake warning indicator to the last on/off state, based upon the last known good brake fluid level or parking brake status message.
NOTE: If DTC U0140 is set in the IC, other symptoms may also be present such as Tire Pressure Monitoring System (TPMS), instrument panel backlighting, and door ajar indication.
If the brake fluid level or parking brake status messages are missing for more than 5 seconds, the IC sets DTC U0140 and defaults the brake warning indicator on. If the IC does not receive the ABS status message or the EBD message from the ABS module for more than 5 seconds, the IC sets DTC U0121 and defaults the ABS warning indicator on.
- DTC B2479 (Park Brake Switch Circuit Short to Ground) - an on-demand DTC that sets when the SJB detects a short to ground on the parking brake warning indicator switch input circuit CMC25 (WH/VT) during the module self-test.
- DTC C1125 (Brake Fluid Level Sensor Input Circuit Failure) - a continuous and on-demand DTC that sets in the SJB if the SJB detects an open or a short to ground on the brake fluid level input circuit CMC19 (GY/VT).
NOTE: Both the ABS warning indicator and the brake warning indicator illuminate if the input to turn on the brake warning indicator is received from the ABS module.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- Parking brake warning indicator switch
- Brake fluid level switch
- SJB
- IC
PINPOINT TEST N: THE BRAKE WARNING INDICATOR IS ALWAYS ON
NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
N1-N7:
N7-N9:
N9-N12:
N12 Continued:
