Chevrolet Silverado / GMC Sierra. Service manual — part 2795

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 C1112

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 C1112

Trailer Brake Control Relay Low Control Circuit - Relay Control Active Low

Diagnostic Fault Information

Circuit/System Description

The trailer brake control module (TBCM) diagnostic monitor detects faults on the solid state
relay (SSR) relay control active low circuit.

Circuit

Short to

Ground

High

Resistance

Open

Short to

Voltage

Signal

Performance

Relay Control Active Low
Circuit

C1112

-

C1112

C1112

-

TBCM Relay Control Circuit

C1112

-

C1112

C1112

-

SSR Fuse STUD 2 Power
Circuit

-

-

C1112

-

-

2008 Chevrolet Silverado 1500

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

Conditions for Running the DTC

The ignition is ON.

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

The 5 volt supply for the SSR output auxiliary supply circuit is not faulted, and DTC C0870
is not set as current DTC.

The SSR relay control circuit fault DTC C1114 is not set as current DTC.

This DTC runs once per ignition cycle within the enabling conditions.

Conditions for Setting the DTC

DTC C1112 will set as current DTC, if one of the following conditions is true:

The TBCM detects an open in the relay control active low circuit.

The TBCM detects short to ground in the relay control active low circuit.

The TBCM detects short to battery positive in the relay control active low circuit.

The TBCM detects a open power circuit from fuse 65 or 61.

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).

Condition 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 is an aftermarket trailer brake controller, the ITBC must be disconnected. Do not power
both ITBC and aftermarket controllers to control the trailer brakes at the same time.

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

Circuit/System Verification

1. Ignition ON, observe the scan tool brake controls Trailer Brake Relay Status parameter.

The reading should be Enabled or Disabled.

2. Ignition ON, observe the scan tool brake controls TBCM Command Duty Cycle parameter.

The reading should be 0 - 100 percent.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the solid state relay.

2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal F and

ground.

If the test lamp does not illuminate, test the B+ circuit for a short to ground or an
open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test or
replace the trailer brake controller solid state relay.

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

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

5. If all circuits test normal, replace the trailer brake solid state relay.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Trailer Brake Control Module Replacement

Control Module References for TBCM replacement, setup, and programming

DTC C1113

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 C1113 01

Trailer Brake Control Relay High Control Circuit Short to Battery

Diagnostic Fault Information

Circuit

Short to

Ground

High

Resistance

Open

Short to

Voltage

Signal

Performance

SSR Relay Control Circuit

C1113 01

-

C1113 01 C1113 01

-

Trailer Auxiliary Supply

-

-

-

C1113 01

-

2008 Chevrolet Silverado 1500

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