Chevrolet Silverado / GMC Sierra. Manual — part 2801

Visual/Physical Inspection

Inspect for aftermarket devices which could affect the operation of the Trailer Brake
Control system. Refer to Checking Aftermarket Accessories .

For vehicles displaying a TRAILER NOT CONNECTED message with a trailer connected.

Inspect the trailer brake connector and circuits for proper connections, perform the
following steps:

1. Verify SSR circuit 47 pin A to the trailer connector pin C for continuity.

2. Verity SSR circuit 1750 pin B to ground and to the trailer connector pin B for

continuity.

If all circuits test normal the vehicle TBCM system is not at fault, otherwise most associated
circuit faults on the vehicle side will set DTC's in the TBCM.

Insure the trailer is equipped with electric over electric brakes - only trailers equipped with
electric brakes will be recognized and function correctly with TBCM.

If the trailer is equipped with hydraulic brakes this trailer will not be recognized by the
TBCM. The vehicle chassis to trailer connector ground or the trailer ground circuits or
trailer brake electric magnets are likely at fault.

The Trailer brake connector should measure less than 2 ohms of resistance between pins A
& B of the trailer side connector. Note - a minimum of one fully functioning axle of brakes
is required for the TBCM system to function correctly.

Symptoms Testing

Some customers may experience an intermittent Check Trailer Wiring message in vehicles
equipped with ITBC (Integrated Trailer Brake Controller) with no DTC stored. This message
may be displayed each time the trailer's running lamps, turn signal lamps or brake lamps turn on -
especially if the trailer is equipped with a large number of lamp loads.

Check Trailer Wiring Message on the DIC

1. Perform the Brake System Vehicle Road Test before using

the Trailer Brake Controls symptom tables in order to
duplicate the customer's concern.

2. Review the system operation in order to familiarize yourself

with the system functions. Refer to the following:

Trailer Brake Controls Description and Operation

ABS Description and Operation (With JL4) ABS
Description and Operation (Without JL4)

2008 Chevrolet Silverado 1500

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

1. This condition is caused by insufficient grounding between the trailer and vehicle.

To correct this condition, perform the following procedure:

Inspect and clean the ground wire (white wire) connection on the trailer side of
the 7-pin connector.

Make sure that the wires inside the trailer side connector are clean and securely
fastened.

If an electrical junction box exists on the trailer, make sure the wires inside the
junction box are clean and securely fastened.

Once this procedure is complete, check to see if the condition has been corrected:

Remove the original trailer ground wire (white wire) from the trailer side of the
7-pin trailer connector.

Install a ring terminal (PN 12103512 or equivalent) to this wire and fasten the
ring terminal to the metal or aluminum chassis of the trailer using a M6x1x20 self
taping phosphate zinc coated screw (PN 11515925 or equivalent).

Pre-drill trailer chassis location with a 3/16" hole. Make sure the trailer chassis
location is clean of paint or coating material prior to installation. Galvanic
corrosion between dissimilar trailer and screw metals may require that this
ground location be periodically cleaned.

Obtain a sufficient length of minimum 10 gauge (5.0 mm2) white wire and fasten with
ring (PN 12103512 or equivalent) terminal to the trailer chassis at the same location as
the original ground wire.

Install and fasten the other end of the new ground wire into the trailer side of the 7-pin
trailer connector.

Install conduit on the original and new trailer ground wires, and secure the conduit to
the existing trailer harness.

2. Verify the condition has been corrected.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to
Testing for Intermittent Conditions and Poor Connections .

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the
symptom:

Brake Warning Indicator Malfunction

2008 Chevrolet Silverado 1500

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

REPAIR INSTRUCTIONS

TRAILER BRAKE CONTROL SWITCH REPLACEMENT

Fig. 3: View Of Trailer Brake Control Switch
Courtesy of GENERAL MOTORS CORP.

TRAILER BRAKE CONTROL MODULE REPLACEMENT

Callout

Component Name

Preliminary Procedure:
Remove the knee bolster. Refer to Knee Bolster Replacement (with RPO SLT) or Knee
Bolster Replacement (without RPO SLT)

1

Trailer Brake Control Switch

Procedure

1. Disconnect the electrical connectors.

2. Use a plastic flat bladed tool to release the switch from the knee bolster

trim.

2008 Chevrolet Silverado 1500

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