Pinpoint Test T: The Brake Warning Indicator is Always On
Instrumentation, Message Center and Warning Chimes
Pinpoint Test T: The Brake Warning Indicator is Always On
Refer to Wiring Diagram Set 60 (Fusion/Milan/MKZ, Fusion Hybrid, Milan Hybrid, MKZ Hybrid), Instrument Cluster for schematic and connector information. 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 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. The parking brake warning indicator switch is case grounded and the brake fluid level uses an external ground circuit.
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, providing a ground to the SJB 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 monitors the parking brake and the brake fluid level inputs sending the IPC 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 function, the ABS module sends a message to the IPC 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 more than 5 seconds, the IPC sets DTC U0140:00 and defaults the brake warning indicator on. If the IPC does not receive the ABS status message or the EBD message from the ABS module for more than 5 seconds, the IPC sets DTC U0121:00 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.
- DTC C1125 (Brake Fluid Level Sensor Input Circuit Failure) - a continuous and on-demand DTC that sets in the SJB if the SJB detects a short to ground on the brake fluid level input circuit.
NOTE: If DTC U0140:00 is set in the IPC, other symptoms may also be present such as Tire Pressure Monitoring System (TPMS), instrument panel backlighting, and door ajar indication.
NOTE: Whenever the IPC receives an EBD message from the ABS module, the IPC illuminates both the brake warning indicator and the ABS warning indicator simultaneously.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- Parking brake warning indicator switch
- Brake fluid level switch
- ABS concern
- SJB
- IPC
PINPOINT TEST T: 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.
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T1 CARRY OUT THE IPC INDICATOR LAMP CONTROL ACTIVE COMMAND USING THE SCAN TOOL
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: IPC DataLogger .
- Select the IPC brake warning indicator (PBA_LMP) active command. Command brake warning indicator on and off while observing the brake warning indicator.
- Does the brake warning indicator turn off when commanded off?
Yes
GO to T2.
No
INSTALL a new IPC. REFER to Instrument Panel Cluster (IPC) Instrument Panel Cluster (IPC). TEST the system for normal operation.
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T2 RETRIEVE THE RECORDED DTCs FROM THE IPC SELF-TEST
- Check for recorded DTCs from the IPC self-test.
- Are any DTCs recorded?
Yes
For DTC U0140:00, GO to Pinpoint Test BM. Pinpoint Tests BM: DTC U0140:00
For DTC U0121:00, GO to Pinpoint Test BK. Pinpoint Tests BK: DTC U0121:00
For all other DTCs, REFER to DTC Charts. Instrumentation, Message Center and Warning Chimes
No
GO to T3.
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T3 RETRIEVE THE RECORDED DTCs FROM THE ABS MODULE SELF-TEST
- Check for recorded DTCs from the ABS module self-test.
- Are any DTCs recorded?
Yes
REFER to Vehicle Dynamic Systems Testing and Inspection.
No
GO to T4.
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T4 RETRIEVE THE RECORDED DTCs FROM THE SJB SELF-TEST
- Check for recorded DTCs from the SJB self-test.
- Is DTC B2479 recorded?
Yes
GO to T5.
No
GO to T8.
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T5 CHECK THE PARKING BRAKE WARNING INDICATOR SWITCH PID
- Enter the following diagnostic mode on the scan tool: SJB DataLogger .
- Select the SJB parking brake PID (PRK_BRAKE). Monitor the parking brake PID while applying and releasing the parking brake.
- Does the PID agree with the parking brake position?
Yes
GO to T10.
No
GO to T6.
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T6 CHECK THE PARKING BRAKE WARNING INDICATOR SWITCH
- Disconnect: Parking Brake Warning Indicator Switch C306 .
- Enter the following diagnostic mode on the scan tool: SJB DataLogger .
- Select the SJB parking brake PID (PRK_BRAKE). Monitor the parking brake PID.
- Does the PID indicate the parking brake is released or off?
Yes
INSTALL a new parking brake warning indicator switch. CLEAR the DTCs. REPEAT the self-test.
No
GO to T7.
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T7 CHECK CIRCUIT CMC25 (WH/VT) FOR A SHORT TO GROUND
- Ignition OFF.
- Disconnect: SJB C2280c .
- Measure the resistance between the SJB C2280c-1, circuit CMC25 (WH/VT), harness side and ground.
- Is the resistance greater than 10,000 ohms?
Yes
GO to T10.
No
REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test.
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T8 CHECK THE BRAKE WARNING INDICATOR USING THE BRAKE FLUID LEVEL SWITCH
- Ignition OFF.
- Disconnect: Brake Fluid Level Switch C124 .
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: SJB Self-Test .
- Clear the SJB DTCs. Repeat the self-test.
- Is DTC C1125 still present?
Yes
GO to T9.
No
INSTALL a new brake fluid level switch. CLEAR the DTCs. REPEAT the self-test.
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T9 CHECK THE BRAKE FLUID LEVEL INPUT CIRCUIT FOR A SHORT TO GROUND
- Ignition OFF.
- Disconnect: SJB C2280f .
- Measure the resistance between the SJB C2280f-9, circuit CMC19 (GY/VT), harness side and ground.
- Is the resistance greater than 10,000 ohms?
Yes
GO to T10.
No
REPAIR the circuit. TEST the system for normal operation.
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T10 CHECK FOR CORRECT SJB OPERATION
- Disconnect all the SJB connectors.
- Check for:
- corrosion
- damaged pins
- pushed-out pins
- Connect all the SJB connectors and make sure they seat correctly.
- Operate the system and verify that the concern is still present.
- Is the concern still present?
Yes
INSTALL a new SJB. REFER to Multifunction Electronic Modules Service and Repair. 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.
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