Chevrolet Silverado / GMC Sierra. Manual — part 2790
system and where the procedure is located.
DTC B3894
Diagnostic Instructions
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
Strategy Based Diagnosis for an overview of the diagnostic approach.
Diagnostic Procedure Instructions provide an overview of each diagnostic category.
DTC Descriptor
DTC B3894 5A
Stop Lamp Switch Circuit Plausibility Failure
Circuit/System Description
The TCC Brake Switch signal hard wired to the TBCM is normally open and closes to battery
voltage when the brake pedal is applied. A separate brake switch signal is hard wired to the Body
Control Module (BCM) that is normally closed to battery voltage and opens when the brake
pedal is applied. The BCM sends its brake switch information to the TBCM over GMLAN serial
data. The TBCM compares the states of the two brake switch signals after a Master Cylinder
Brake Pressure threshold is exceeded. If the brake switch signal states are not in agreement or if
the serial data brake state is not valid, a DTC will set and the ITBC system will be disabled.
Conditions for Running the DTC
The system voltage is in the range of 9.5-17 volts.
The module initialization has taken place.
The master cylinder brake pressure exceeds threshold
Conditions for Setting the DTC
The actual brake switch input to the TBCM, and the serial data information for the brake switch
do not match.
Action Taken When the DTC Sets
The trailer brake control will be disabled for the remainder of the ignition cycle.
Service Trailer Brake System, will be displayed on the driver information center (DIC).
2008 Chevrolet Silverado 1500
2008 BRAKES Trailer Brake Controls - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
Conditions for Clearing the MIL/DTC
Clear DTCs with a scan tool.
Diagnostic Aids
If there are any other DTCs set for the stop lamp or lighting systems, or GMLAN communication
such as U0100, U0121, U0140, or U2099, diagnose them first before to resolve DTCs described
in this section.
Reference Information
Schematic Reference
Trailer Brake Control Schematics
Description and Operation
Trailer Brake Controls Description and Operation
Connector End View Reference
Component Connector End Views
Electrical Information Reference
Circuit Testing
Connector Repairs
Testing for Intermittent Conditions and Poor Connections
Wiring Repairs
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for Scan Tool Information
Circuit/System Verification
Ignition ON, press the brake pedal. The brake lights should illuminate, and scan tool data list
2008 Chevrolet Silverado 1500
2008 BRAKES Trailer Brake Controls - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
Brake Switch Status should indicate ON.
Circuit/System Testing
1. Disconnect the stop lamp switch and test for short to ground between terminal A of the stop
lamp switch connector and terminal 37 of the TBCM.
If the circuit test normal, replace the stop lamp switch.
2. Test for short to battery positive between terminal A of the stop lamp switch connector and
terminal 37 of the TBCM.
If all circuits/connections test normal, replace the TBCM.
Repair Procedures
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for TBCM replacement, setup, and programming
DTC C0561
Diagnostic Instructions
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
Review Strategy Based Diagnosis for an overview of the diagnostic approach.
Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptor
DTC C0561 F0
System Disabled Information Stored Invalid Serial Data Received
DTC C0561 F1
System Disabled Information Stored Invalid Serial Data Received
Circuit/System Description
Diagnostics are used to determine whether or not there is a fault with the brake pressure or wheel
speed data being received by the TBCM over GMLAN serial data.
The loss of serial data brake pressure diagnostic is to determine whether or not there is a fault
with the brake pressure data being received over GMLAN. This diagnostic looks at the brake
2008 Chevrolet Silverado 1500
2008 BRAKES Trailer Brake Controls - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
pressure signal validity and protection value signals over a period of time to determine the fault
state of the brake pressure sensor.
The loss of serial data wheel speed diagnostic is to determine whether or not there is a fault with
the wheel speed data being received over GMLAN. This diagnostic looks at the wheel speed
signal validity and sequence number errors over a period of time to determine the fault state
Conditions for Running the DTC
The ignition switch is in the ON position.
Ignition voltage is in the range of 9.5-17 volts.
Conditions for Setting the DTC
The EBCM diagnoses a fault condition in the master cylinder pressure sensor, and sends a
serial data message to the TBCM.
The EBCM diagnoses a fault condition in the wheel speed sensors, and sends a serial data
message to the TBCM.
The TBCM losses communication with the EBCM.
Action Taken When the DTC Sets
One or more of the following actions may occur:
The trailer brake control will be disabled for the remainder of the ignition cycle.
Service Trailer Brake System will be displayed on the Driver Information Center (DIC).
Conditions for Clearing the DTC
The condition for the DTC is no longer present.
The TBCM automatically clears the history DTC when a current DTC is not detected in 40
consecutive drive cycles.
Diagnostic Aids
If there are any DTCs set for GMLAN communication such as U0100, U0121, U0140, or U2099
or the antilock brake control system, diagnose them first before to resolve DTCs described in this
section.
Check for Brake Pressure Sensor and/or Wheel Speed Sensor DTCs in EBCM. Follow EBCM
circuit repair procedure. If no DTCs are found in EBCM check for ground differential between
EBCM and TBCM, loose TBCM ground, loose GMLAN signal terminal pins at TBCM or source
2008 Chevrolet Silverado 1500
2008 BRAKES Trailer Brake Controls - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
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