Pinpoint Test S: The Brake Warning Indicator is Never On
Instrumentation, Message Center and Warning Chimes
Pinpoint Test S: The Brake Warning Indicator is Never On
Refer to Wiring Diagram Set 60, Instrument Cluster for schematic and connector information. [1][2]Diagrams By Number
Normal Operation
The Instrument Panel Cluster (IPC) 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) and the brake booster vacuum sensor, controlled by the ABS module. 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 (Electronic Brake Distribution) message is sent from the ABS module over the High Speed Controller Area Network (HS-CAN) communication bus lines. The parking brake warning indicator switch and brake fluid level switch are both hardwired to the SJB (Smart Junction Box). The parking brake warning indicator switch is case grounded and the brake fluid level uses an external ground circuit.
The SJB (Smart Junction Box) 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, providing a ground to the SJB (Smart Junction Box) and pulling the parking brake input circuit low. When a low brake fluid level condition exists, the low brake fluid level switch closes to ground through the ground circuit, pulling the brake fluid level input circuit low. The SJB (Smart Junction Box) monitors the parking brake and the brake fluid level inputs sending the IPC (Instrument Panel Cluster) a message to turn the brake warning indicator on or when the parking brake is applied. When the ABS module detects a base brake system concern or other ABS-related concerns that affect the EBD (Electronic Brake Distribution) function, the ABS module sends a message to the IPC (Instrument Panel 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
- Parking brake warning indicator switch
- Brake fluid level switch
- SJB (Smart Junction Box)
- IPC (Instrument Panel Cluster)
PINPOINT TEST S : THE BRAKE WARNING INDICATOR IS NEVER ON
NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
NOTE: Failure to disconnect the battery when instructed will result in false resistance readings.
S1 CARRY OUT THE IPC (Instrument Panel Cluster) INDICATOR LAMP CONTROL ACTIVE COMMAND USING THE SCAN TOOL
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: IPC (Instrument Panel Cluster) DataLogger.
- Select the IPC (Instrument Panel Cluster) brake warning indicator (PBA_LMP) active command. Command the brake warning indicator on while observing the brake warning indicator.
Does the brake warning indicator illuminate when commanded on?
Yes
GO to S2.
No
INSTALL a new IPC (Instrument Panel Cluster). REFER to Instrument Panel Cluster (IPC) . TEST the system for normal operation.
S2 DETERMINE IF THE BRAKE WARNING INDICATOR OPERATES WITH THE PARKING BRAKE
- Apply the parking brake while monitoring the brake warning indicator.
Does the brake warning indicator illuminate with the parking brake applied?
Yes
GO to S6.
No
GO to S3.
S3 CHECK THE PARKING BRAKE WARNING INDICATOR SWITCH PID
- Enter the following diagnostic mode on the scan tool: SJB (Smart Junction Box) DataLogger.
- Select the SJB (Smart Junction Box) parking brake PID (PRK_BRK). Monitor the parking brake PID while applying the parking brake.
Does the PID agree with the parking brake position?
Yes
GO to S9.
No
GO to S4.
S4 CHECK THE PARKING BRAKE WARNING INDICATOR SWITCH
- Disconnect: Parking Brake Warning Indicator Switch C306.
- Connect a fused jumper wire between the parking brake warning indicator switch C306-1, circuit CMC25 (WH/VT), harness side and ground.
Does the brake warning indicator illuminate?
Yes
REMOVE the jumper wire. INSTALL a new parking brake warning indicator switch. TEST the system for normal operation.
No
REMOVE the jumper wire. GO to S5.
S5 CHECK THE PARKING BRAKE SIGNAL CIRCUIT FOR AN OPEN
- Disconnect: SJB (Smart Junction Box) C2280C.
- Measure the resistance between the SJB (Smart Junction Box) C2280C-1, circuit CMC25 (WH/VT), harness side and the parking brake warning indicator switch C306-1, circuit CMC25 (WH/VT), harness side and ground.
Is the resistance less than 5 ohms?
Yes
GO to S9.
No
REPAIR the circuit. TEST the system for normal operation.
S6 CHECK THE BRAKE FLUID LEVEL SWITCH OPERATION
- Ignition OFF.
- Disconnect: Brake Fluid Level Switch C124.
- Ignition ON.
- Connect a fused jumper wire between the brake fluid level switch C124-1, circuit CMC19 (GY/VT), harness side and the brake fluid level switch C124-2, circuit GD121 (BK/YE), harness side.
Does the brake warning indicator illuminate?
Yes
REMOVE the jumper wire. INSTALL a new brake fluid level switch. TEST the system for normal operation.
No
REMOVE the jumper wire. GO to S7.
S7 CHECK THE BRAKE FLUID LEVEL SWITCH GROUND CIRCUIT FOR AN OPEN
- Ignition OFF.
- Disconnect: Negative Battery Cable.
- Measure the resistance between the brake fluid level switch C124-2, circuit GD121 (BK/YE), harness side and ground.
Is the resistance less than 5 ohms?
Yes
GO to S8.
No
REPAIR the circuit. TEST the system for normal operation.
S8 CHECK THE BRAKE FLUID LEVEL INPUT CIRCUIT FOR AN OPEN
- Disconnect: SJB (Smart Junction Box) C2280F.
- Measure the resistance between the SJB (Smart Junction Box) C2280F-9, circuit CMC19 (GY/VT), harness side and the brake fluid level switch C124-1, circuit CMC19 (GY/VT), harness side.
Is the resistance less than 5 ohms?
Yes
GO to S9.
No
REPAIR the circuit. TEST the system for normal operation.
S9 CHECK FOR CORRECT SJB (Smart Junction Box) OPERATION
- Disconnect all the SJB (Smart Junction Box) connectors.
- Check for:
- corrosion
- damaged pins
- pushed-out pins
- Connect all the SJB (Smart Junction Box) connectors and make sure they seat correctly.
- Operate the system and verify the concern is still present.
Is the concern still present?
Yes
INSTALL a new SJB (Smart Junction Box). TEST the system for normal operation.
No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.