Pinpoint Test S: The Brake Warning Indicator is Always On
Instrumentation, Message Center and Warning Chimes
Pinpoint Tests
Pinpoint Test S: The Brake Warning Indicator is Always On
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 the 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 and the brake fluid level switch are hardwired to the SJB through separate signal and return circuits. The brake fluid level switch is hardwired to the SJB through brake fluid level signal and return circuits.
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 signal circuit 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, pulling the brake fluid level signal circuit 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 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 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.
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.
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
- IC
PINPOINT TEST S: 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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S1 CARRY OUT THE IC INDICATOR LAMP CONTROL ACTIVE COMMAND USING THE SCAN TOOL
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: IC DataLogger .
- Select the IC brake warning indicator (BRK_LAMP) active command. Command the brake warning indicator on and off. Observe the brake warning indicator.
- Does the brake warning indicator turn off when commanded off?
Yes
GO to S2.
No
INSTALL a new IC. REFER to Instrument Cluster (IC) Instrument Cluster (IC). TEST the system for normal operation.
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S2 RETRIEVE THE RECORDED DTCs FROM THE IC SELF-TEST
- Check for recorded IC DTCs from the self-test.
- Are any DTCs recorded?
Yes
For DTC U0140, GO to Pinpoint Test BH. Pinpoint Tests BH: DTC U0140
For DTC U0121, GO to Pinpoint Test BF. Pinpoint Tests BF: DTC U0121
For all other DTCs, REFER to DTC Chart. Instrumentation, Message Center and Warning Chimes
No
GO to S3.
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S3 RETRIEVE THE RECORDED DTCs FROM THE SJB SELF-TEST
- Check for recorded SJB DTCs from the self-test.
- Is DTC C1125 recorded?
Yes
GO to S9.
No
GO to S4.
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S4 RETRIEVE THE RECORDED DTCs FROM THE ABS MODULE SELF-TEST
- Check for recorded ABS module DTCs from the self-test.
- Are any DTCs recorded?
Yes
REFER to Antilock Brakes / Traction Control Systems.
No
GO to S5.
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S5 CHECK THE PARKING BRAKE WARNING INDICATOR SWITCH PID
- Enter the following diagnostic mode on the scan tool: SJB DataLogger .
- Select the SJB parking brake (PRK_BRAKE) PID.
- Monitor the parking brake PID while applying and releasing the parking brake.
- Does the PID agree with the parking brake position?
Yes
GO to S13.
No
GO to S6.
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S6 CHECK THE PARKING BRAKE WARNING INDICATOR SWITCH
- Disconnect: Parking Brake Warning Indicator Switch C2015 .
- Enter the following diagnostic mode on the scan tool: SJB DataLogger .
- Select the SJB parking brake (PRK_BRAKE) PID.
- 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
For 6.4L diesel, GO to S7.
For all others, GO to S8.
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S7 CHECK THE PCM
- Ignition OFF.
- Disconnect: PCM C1232b .
- Ignition ON.
- Monitor the parking brake PID.
- Does the PID indicate the brake is released or off?
Yes
GO to S14.
No
GO to S8.
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S8 CHECK THE PARKING BRAKE WARNING INDICATOR SWITCH INPUT CIRCUIT 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 S13.
No
REPAIR circuit CMC25 (WH/VT) for a short to ground. CLEAR the DTCs. REPEAT the self-test.
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S9 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 CMC19 (GY/VT), harness side and the brake fluid level switch C124-3, circuit RMC19 (YE/GY), harness side.
- Ignition ON.
- Does the brake warning indicator turn off?
Yes
REMOVE the jumper wire. INSTALL a new master cylinder. REFER to Hydraulic System, Brakes &/or Brake Pedal Assy. REPEAT the self-test. CLEAR the DTCs.
No
REMOVE the jumper wire. GO to S10.
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S10 CHECK THE BRAKE FLUID LEVEL SWITCH INPUT CIRCUIT FOR AN OPEN
- Ignition OFF.
- Disconnect: SJB C2280f .
- Measure the resistance between the SJB C2280f-9, circuit CMC19 (GY/VT), harness side and the brake fluid level switch C124-2, circuit CMC19 (GY/VT), harness side.
- Is the resistance less than 5 ohms?
Yes
GO to S11.
No
REPAIR circuit CMC19 (GY/VT) for an open. TEST the system for normal operation.
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S11 CHECK THE BRAKE FLUID LEVEL SWITCH RETURN CIRCUIT FOR AN OPEN
- Measure the resistance between the SJB C2280f-22, circuit RMC19 (YE/GY), harness side and the brake fluid level switch C124-3, circuit RMC19 (YE/GY), harness side.
- Is the resistance less than 5 ohms?
Yes
GO to S12.
No
REPAIR circuit RMC19 (YE/GY) for an open. TEST the system for normal operation.
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S12 CHECK THE BRAKE FLUID LEVEL SWITCH INPUT AND RETURN CIRCUITS FOR A SHORT TO GROUND
- Measure the resistance between the SJB C2280f-9, circuit CMC19 (GY/VT), harness side and ground; and between the SJB C2280f-22, circuit RMC19 (YE/GY), harness side and ground.
- Are the resistances greater than 10,000 ohms?
Yes
GO to S13.
No
REPAIR the circuit in question. TEST the system for normal operation.
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S13 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 the concern is still present.
- Is the concern still present?
Yes
INSTALL a new SJB. REFER to Body Control Systems. 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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S14 CHECK FOR CORRECT PCM OPERATION
- Disconnect all the PCM connectors.
- Check for:
- corrosion
- damaged pins
- pushed-out pins
- Connect all the PCM 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 PCM. REFER to Computers and Control Systems. 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. CLEAR the DTCs. REPEAT the self-test.
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