Service Trailer Brake Message With DTC C1114 and/or C1112 - keywords connector module TBCM tow 7 way wheel tire

This PI has been superceded to provide additional fix information. Please discard PIT4595.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Some owners may comment of a Service Trailer Brake System message displayed on the DIC. When checking for DTC’s, C1112 or C1114 will be set in the Trailer Brake Control Module (TBCM). This concern may occur with or without a trailer connected to the vehicle.

GM is receiving a number of returned Trailer Brake Control Modules (TBCM) and Trailer Brake Relays that test completely functional. The TBCM monitors the voltage of the electric brake wire (blue) that runs from the trailer brake relay to the 7-pin trailer connector in the bumper. If the voltage on this wire is shorted lower or higher than the designed output voltage of the relay the TBCM is designed to set a DTC.

Please investigate all wiring between the trailer brake relay and the 7-pin trailer connector (including any 5th wheel jumpers/connectors) for damaged wiring/connectors (nicks, cuts, corrosion, pin damage, etc.) and poor quality or non-sealed splices. Even a small amount of water intrusion will wick its way to both the trailer brake relay and the 7-pin trailer connector in the bumper, potentially causing intermittent DTCs.

Please follow the procedure below to eliminate the possibility of a short causing this condition. Engineering is requesting to be contacted if the following procedure does not identify the root cause. Please follow this diagnostic path PRIOR to making contact with the engineer listed below. Please provide as complete of an answer as possible for the following questions:

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

IMMEDIATE DIAGNOSIS

1. Check for blown fuses related to the trailer brake system.
2. Disconnect trailer harness (if trailer is with vehicle).
3. Examine vehicle for unsealed splices or damage in vehicle trailer wiring (including 5th wheel wiring harnesses).
4. Examine G401 ground for corrosion or poor connection. Clean as required.
5. With the ignition on, use the Tech 2 to monitor TBCM Relay Feedback Signal. Monitor signal for 10-15 seconds. Determine the minimum voltage value that occurs. (This voltage varies once per second and always settles down to the minimum.)
6. The minimum voltage should be between 3.4 - 3.8 V.

- If the voltage is higher or lower - go to the Short Investigation (see section A below)

- If the Service Trailer Brake Message appears - go to the Short Investigation (see section A below)

7. Repeat step 5 with brake applied for 10 seconds.
8. The minimum voltage should be between 3.4 - 3.8 V.

- If the voltage is higher or lower - go to the Short Investigation (see section A below)

- If Service Trailer Brake Message appears - go to the Short Investigation (see section A below)

9. Repeat step 5 with the vehicle in reverse and brake applied for 10 seconds.
10. The minimum voltage should be between 3.4 - 3.8 V.

- If the voltage is higher or lower - go to the Short Investigation (see section A below)

- If Service Trailer Brake Message appears - go to the Short Investigation (see section A below)

11. If any damage to the wiring harness or splices are found in step 3, spray with water and repeat steps 5 - 10.
12. If no issues were found in the previous steps, follow the service procedure in SI for DTCs C1112/C1114 prior to performing the next step.
13. Go to the contacting engineer section (see section B below)

SECTION A - Short Investigation

Investigate wiring for shorts between the trailer brake (electric brake) wire (blue) and any/all of the following trailer wires: Right Turn/Brake, Left Turn/Brake, Running Lights, Back Up, Battery, Ground. Please note that splices covered with heat shrink tubing are not always water tight and may be an area of concern.

SECTION B - Contacting the Engineer - Please answer the following questions:

DEALERSHIP

1. Dealership name and location
2. Main Contact Person and Phone Number

Immediate Diagnosis Questions

3. Please list all trailer brake codes seen in history or set during procedure.
4. Were any low/high voltages seen on Tech 2? Under which conditions?
5. Were any shorts found?
6. What was found following the C1112/C1114 service procedure?

CUSTOMER/TRAILER RELATED INFORMATION

7. Does vehicle have aftermarket 5th wheel harness, UY2 camper harness, or any other accessories (lights, cap, etc) wired into vehicle trailer wiring?

GM Engineering contact information:

Contact the individual below to review the responses to the questions above:

-Contact Hours: 8:00am - 7:00pm EST, Monday through Friday

-Contact Person: Dave Osterman

-Phone Number: 248-318-0379

If necessary, leave a message with the following information:

- Technician Name

- Dealership Name & Phone Number

- Last 8 digits of the VIN and Repair Order #

- Date and time of call

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.