C1115

DTC C1115

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 C1115 08
- Manual Trailer Brake Apply Request Switch Signal Invalid-Manual Apply Switch Stuck Closed

DTC C1115 5A
- Manual Trailer Brake Apply Request Switch Signal Plausibility Failure




Diagnostic Fault Information






Circuit/System Description

The manual apply switch rationality diagnostic monitors for circuit rationality faults on the manual apply switch input. The manual apply switch consists of a primary circuit, which is used as the basis for determining the trailer brake manual apply gain, and a redundant circuit that is used to rationalize performance of the primary circuit.


Manual Trailer Brake Apply Request Switch Signal Invalid" diagnostic monitors for a manual apply switch that is stuck in an applied position.


Manual Trailer Brake Apply Request Switch Signal --plausibility failure diagnostic monitors for circuit rationality faults on the manual apply switch input. The manual apply switch consists of a primary circuit, which is used as the basis for determining the trailer brake manual apply gain, and a redundant circuit that is used to rationalize performance of the primary circuit. The manual apply switch position fault is detected when the absolute value of the difference between the primary manual apply switch input and redundant inputs exceeds a threshold for a certain amount of time.


Conditions for Running the DTC

* DTC C1116 or C1117 are not set as current DTC.
* The system voltage is in the range of 9.5 - 17 volts.
* The module is powered up and completes initialization.



Conditions for Setting the DTC

C1115 08

Manual trailer brake apply request switch signal invalid fault is detected when any one of the following conditions is true:

* The ignition is turned from Off to On, the Manual Apply Switch is not activated, then it is detected that the Manual Apply Switch is activated for 5 minutes.
* The ignition is Off, the Manual Apply is already activated, and then turn on the ignition, and detected the Manual Apply Switch is continuing to be activated for 30 seconds.


C1115 5A

Manual Trailer Brake Apply Request Switch Signal plausibility failure:

* The ignition is turned from Off to On, the Manual Apply Switch is not activated, then it is detected that the Manual Apply Switch is activated for 5 minutes.
* The fault is detected if the absolute value of the difference between the primary manual apply switch input and redundant inputs exceeds a threshold for an extended amount of time.



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


When the manual trailer brake apply switch is shorted to ground, shorted to battery, or open circuit, DTC C1116 Manual Apply Switch Primary input circuit fault may also be set as a current DTC. If DTC C1116 is also set as current DTC, then diagnose DTC C1116 first before to diagnosing DTC C1115 08 and C1115 5A. 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 ([1][2]Electrical Diagrams)
Description and Operation

Trailer Brake Controls 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 Primary Manual Apply parameter. The reading should be between 0-100 percent and change with brake pedal input.
2. Ignition ON, observe the scan tool brake controls Redundant Manual Apply parameter. The reading should be between 0-100 percent and change with brake pedal input.



Circuit/System Testing

Important: All electrical components and accessories must be turned OFF and allowed to power down.



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. Verify the scan tool Manual Apply Switch is less than 10 percent.

• If greater than the specified range, test the signal circuit terminal 4 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 Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

* Control Module References for TBCM replacement, setup, and programming
* Trailer Brake Control Module Replacement (Trailer Brake Control Module Replacement)