Chevrolet Silverado / GMC Sierra. Service 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