Chevrolet Silverado / GMC Sierra. Service manual — part 2794

Internal TBCM circuit reference voltage for User Gain switch is below 4.8 volts or above 5.2
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 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 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.

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

2008 Chevrolet Silverado 1500

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

Scan Tool Reference

Control Module References for Scan Tool Information

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the trailer brake controller switch panel.

2. Test for less than 5 ohms of resistance between the ground circuit terminal 8 and ground.

If greater than the specified range, test the ground circuit for an open/high resistance.
If the circuit tests normal, replace the TBCM.

3. Ignition ON, test for 4.8 - 5.2 volts between the 5-volt reference circuit terminal 6 and

ground.

If less than the specified range, test the 5-volt reference circuit for a short to ground or
an open/high resistance. If the circuit tests normal, replace the TBCM.

If greater than the specified range, test the 5-volt reference circuit for a short to
voltage. If the circuit tests normal, replace the TBCM.

4. If all circuits test normal, test or replace the trailer brake controller switch panel.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for TBCM replacement, setup, and programming

DTC C0890

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 C0890

Device Voltage Reference Output 3 Circuit

IMPORTANT: All electrical components and accessories must be turned OFF

and allowed to power down.

2008 Chevrolet Silverado 1500

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

Diagnostic Fault Information

Circuit/System Description

The TBCM runs this diagnostics to check whether there is a fault on the internal TBCM 5 volt
references used to monitor the Manual Apply switch circuits. This diagnostics checks if the
circuits 5 volt references is within a range for normal operation.

Conditions for Running the DTC

The system voltage is in the range of 9.5 - 17 volts.

The module initialization has taken place.

Conditions for Setting the DTC

The TBCM detects voltage greater than 5.2 volts in the manual apply switch 5 volt reference
circuit.

The TBCM detects voltage less than 4.8 volts in the manual apply switch 5 volt reference circuit.

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.

A message center or an indicator displays.

Conditions for Clearing the 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 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.

Circuit

Short to

Ground

High

Resistance

Open

Short to

Voltage

Signal

Performance

Device Voltage Reference
Output 3 Circuit

C0890

-

-

C0890

-

2008 Chevrolet Silverado 1500

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

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 Testing

1. Ignition OFF, disconnect the harness connector at the trailer brake controller switch panel.

2. Test for less than 5 ohms of resistance between the ground circuit terminal 5 and ground.

If greater than the specified range, test the ground circuit for an open/high resistance.
If the circuit tests normal, replace the TBCM.

3. Ignition ON, test for 4.8 - 5.2 volts between the 5-volt reference circuit terminal 3 and

ground.

IMPORTANT: All electrical components and accessories must be turned OFF

and allowed to power down.

2008 Chevrolet Silverado 1500

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