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
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), 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 is hardwired to the SJB (Smart Junction Box) through an input circuit. The brake fluid level switch is hardwired to the SJB (Smart Junction Box) through independent signal and return circuits.
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 input circuit low. When a low brake fluid level condition exists, the low brake fluid level switch closes to ground, pulling the 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 when the parking brake is applied, when the brake fluid level is low or if the SJB (Smart Junction Box) detects an open in the brake fluid level signal or return circuits. 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.
If the brake fluid level or parking brake status messages are missing for less than 5 seconds, the IPC (Instrument Panel Cluster) 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.
If the brake fluid level or parking brake status messages are missing for more than 5 seconds, the IPC (Instrument Panel Cluster) sets DTC U0140:00 and defaults the brake warning indicator on. If the IPC (Instrument Panel Cluster) does not receive the ABS status message or the EBD (Electronic Brake Distribution) message from the ABS (Anti-Lock Brake System) module for more than 5 seconds, the IPC (Instrument Panel Cluster) 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 (Smart Junction Box) detects a short to ground on the parking brake warning indicator switch input circuit 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 (Smart Junction Box) if the SJB (Smart Junction Box) detects an open or short to ground on the brake fluid level input circuit.
NOTE: If DTC U0140:00 is set in the IPC (Instrument Panel Cluster), other symptoms may also be present such as Tire Pressure Monitoring System (TPMS) or instrument panel backlighting.
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 (part of the master cylinder)
- ABS concern
- SJB (Smart Junction Box)
- IPC (Instrument Panel Cluster)
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 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 and off while observing the brake warning indicator.
Does the brake warning indicator turn off when commanded off?
Yes
GO to N2.
No
INSTALL a new IPC (Instrument Panel Cluster). REFER to Instrument Panel Cluster (IPC) . TEST the system for normal operation.
N2 RETRIEVE THE RECORDED DTCs FROM THE IPC (Instrument Panel Cluster) SELF-TEST
- Check for recorded DTCs from the IPC (Instrument Panel Cluster) self-test.
Are any DTCs recorded?
Yes
For DTC U0140:00, GO to Pinpoint Test AY. Pinpoint Test AY: DTC U0140:00
For DTC U0121:00, GO to Pinpoint Test AW. Pinpoint Test AW: DTC U0121:00
For all other DTCs, REFER to DTC Charts. Instrumentation, Message Center and Warning Chimes
No
GO to N3.
N3 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 Antilock Brakes / Traction Control Systems.
No
GO to N4.
N4 RETRIEVE THE RECORDED DTCs FROM THE SJB (Smart Junction Box) SELF-TEST
- Check for recorded DTCs from the SJB (Smart Junction Box) self-test.
Is DTC B2479 recorded?
Yes
GO to N5.
No
GO to N8.
N5 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_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 N12.
No
GO to N6.
N6 CHECK THE PARKING BRAKE WARNING INDICATOR SWITCH
- Disconnect: Parking Brake Warning Indicator Switch C2015.
- Enter the following diagnostic mode on the scan tool: SJB (Smart Junction Box) DataLogger.
- Select the SJB (Smart Junction Box) 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 N7.
N7 CHECK THE PARKING BRAKE INPUT CIRCUIT FOR A SHORT TO GROUND
- Ignition OFF.
- Disconnect: SJB (Smart Junction Box) C2280C.
- Measure the resistance between the SJB (Smart Junction Box) C2280C-1, circuit CMC25 (WH/VT), harness side and ground.
Is the resistance greater than 10,000 ohms?
Yes
GO to N12.
No
REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test.
N8 CHECK THE BRAKE WARNING INDICATOR USING THE FLUID LEVEL SWITCH
- Ignition OFF.
- Disconnect: Brake Fluid Level Switch C124.
- Connect a fused jumper wire between the brake fluid level switch C124-2, circuit RMC19 (YE/GY), harness side and the brake fluid level switch C124-3, circuit CMC19 (GY/VT), harness side.
- Ignition ON.
Does the brake warning indicator turn off?
Yes
REMOVE the jumper wire. INSTALL a new master cylinder. REPEAT the self-test. CLEAR the DTCs.
No
REMOVE the jumper wire. GO to N9.
N9 CHECK THE BRAKE FLUID LEVEL INPUT CIRCUIT FOR AN OPEN
- Ignition OFF.
- 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 C124-3, circuit CMC19 (GY/VT), harness side.
Is the resistance less than 5 ohms?
Yes
GO to N10.
No
REPAIR the circuit. TEST the system for normal operation.
N10 CHECK THE BRAKE FLUID LEVEL RETURN CIRCUIT FOR AN OPEN
- Measure the resistance between the SJB (Smart Junction Box) C2280F-22, circuit RMC19 (YE/GY), harness side and the brake fluid level switch C124-2, circuit RMC19 (YE/GY), harness side.
Is the resistance less than 5 ohms?
Yes
GO to N11.
No
REPAIR the circuit. TEST the system for normal operation.
N11 CHECK THE BRAKE FLUID LEVEL INPUT AND RETURN CIRCUITS FOR A SHORT TO GROUND
- Measure the resistance between the SJB (Smart Junction Box) C2280F-9, circuit CMC19 (GY/VT), harness side and ground; and between the SJB (Smart Junction Box) C2280F-22, circuit RMC19 (YE/GY), harness side and ground.
Are the resistances greater than 10,000 ohms?
Yes
GO to N12.
No
REPAIR the circuit in question. TEST the system for normal operation.
N12 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 that 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.