Chevrolet Silverado / GMC Sierra. Service manual — part 2792

The trailer brake control module (TBCM) monitors the system voltage (ignition voltage) to make
sure that the voltage stays within the proper range. Damage to components, and incorrect data
input can occur when the voltage is out of range. The TBCM monitors the system voltage over an
extended length of time. If the TBCM detects a system voltage outside an expected range, DTC
C0800 will set.

Conditions for Running the DTC

The ignition is ON.

The engine speed is greater than 400 RPM.

Conditions for Setting the DTC

C0800 03

During initialization or when the system is inactive, the system voltage is less than 10.5
volts.

During the system operation, the system voltage is less than 9.5 volts.

C0800 07

Ignition is in RUN.

The system voltage is greater than 17 volts.

Action Taken When the DTC Sets

The trailer brake control will be disabled at the end of the current brake apply for the
remainder of the ignition cycle.

The Service Trailer Brake System will be displayed on the Driver Information Center
(DIC).

Conditions for Clearing the MIL/DTC

When 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.

Reference Information

Schematic Reference

Trailer Brake Control Schematics

2008 Chevrolet Silverado 1500

2008 BRAKES Trailer Brake Controls - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

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

Scan Tool Reference

Control Module References for Scan Tool Information

Diagnostic Aids

If there are any other DTCs set for GMLAN communication such as U0100, U0121, U0140, or
U2099, diagnose them first before to resolve DTCs described in this section.

C0800 03

Test the charging system Refer to Diagnostic System Check - Vehicle .

Possible causes of this DTC are the following conditions:

A charging system malfunction

An excessive battery draw

A weak battery

A faulty system ground

C0800 07

Test the charging system Refer to Diagnostic System Check - Vehicle .

A possible cause of this DTC is overcharging.

Circuit/System Verification

2008 Chevrolet Silverado 1500

2008 BRAKES Trailer Brake Controls - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

With the scan tool installed, ignition ON and the engine running, observe the Battery Positive
Voltage parameter in the TBCM data list. The reading should be between 9-17 volts.

Circuit/System Testing

1. If the DTC is history, refer to Charging System Test .

2. If the DTC is current, start the engine, and measure the voltage between the battery positive

voltage circuits of the TBCM and the ground circuit.

If the voltage is within 9-17 volts, replace the affected module.

If the voltage is not within 9-17 volts, measure the voltage between the battery positive
voltage circuits of the TBCM and a separate good ground.

If the voltage is within 9-17 volts, test the battery positive ground circuits of the
TBCM for high resistance or an open, and repair as necessary.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for TBCM replacement, setup, and programming

DTC C0845

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 C0845 03

Device Ignition 1 Circuit Voltage Below Threshold

Diagnostic Fault Information

Circuit

Short to

Ground

High

Resistance

Open

Short to

Voltage

Signal

Performance

Ignition 1 Circuit

-

-

C0845 03

-

-

TCC Brake Signal Circuit

C0845 03

-

-

-

-

2008 Chevrolet Silverado 1500

2008 BRAKES Trailer Brake Controls - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Circuit/System Description

The trailer brake control module (TBCM) checks whether there is an ignition ground short fault.
This diagnostic compares ignition state with the engine running state received over serial data to
determine whether or not there is an ignition ground short fault.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

The engine is running, and the TBCM detects that the IGN 1 voltage is less than 9.2 volts

Action Taken When the DTC Sets

The trailer brake control will be disabled for the remainder of the ignition cycle.

The Service Trailer Brake System will be displayed on the Driver Information Center
(DIC).

Conditions for Clearing the MIL/DTC

When 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 other DTCs set for GMLAN communication such as U0100, U0121, U0140, or
U2099, diagnose them first before resolving DTCs described in this section.

Reference Information

Schematic Reference

Trailer Brake Control Schematics

Description and Operation

Trailer Brake Controls Description and Operation

IMPORTANT: The ignition may need to be cycled twice, waiting 30 seconds

between key cycles, to move the code from current to history

2008 Chevrolet Silverado 1500

2008 BRAKES Trailer Brake Controls - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado