Bulletin No.: PIT5509M

Service Bulletin

Date: May, 2026

PRELIMINARY INFORMATION
Subject:

Brand:

Diagnostic Tip - Check and/or Service Trailer Brake System message DTC
C1114
Model:

Model Year:
from

VIN:
to

from

Engine:

Transmission:

to

Cadillac

Escalade

2021 - 2024

All

All

All

All

Cadillac

Escalade
ESV

2021 - 2024

All

All

All

All

Chevrolet

Colorado

2015 - 2026

All

All

All

All

Chevrolet

Silverado
1500

2014 - 2026

All

All

All

All

Chevrolet

Silverado
2500/3500

2015 - 2026

All

All

All

All

Chevrolet

Suburban

2015 - 2024

All

All

All

All

Chevrolet

Tahoe

2015 - 2024

All

All

All

All

GMC

Canyon

2015 - 2026

All

All

All

All

GMC

Sierra 1500

2014-2026

All

All

All

All

GMC

Sierra
2500/3500

2015 - 2026

All

All

All

All

GMC

Yukon

2015 - 2024

All

All

All

All

GMC

Yukon XL

2015 - 2024

All

All

All

All

With Integrated Trailer Brake Control (ITBC) system RPO JL1
Supersession Statement
This PI was superseded to update the Models. Please discard PIT5509L.

Condition / Concern
Some customers may comment that when they have a trailer connected to the vehicle, they get a "Check Trailer
Wiring" or "Service Trailer Brake System" message on the DIC. DTC C1114 could be set in the Chassis Control
Module/Chassis Control Module Auxiliary/Brake System Control Module.
Diagnosing these concerns can be difficult because the issue could either be related to the truck or the trailer. This
PI is to provide some additional diagnostic information for these three symptoms:
-

Check Trailer Wiring message

-

Check Trailer Wiring message with DTC C1114

-

Service Trailer Brake System message with DTC C1114

Copyright 2026 General Motors. All Rights Reserved.

Page 2

May, 2026

Bulletin No.: PIT5509M

General Information
The trailer brake control system on the new body style trucks is compatible with two types of trailer brake systems:
electromagnetic or electro-over hydraulic trailer brakes. The Chassis Control Module K38 (CCM), Chassis Control
Module Auxiliary K38A or Brake System Control Module K160 (BSCM) depending on the model year, must
determine which type of brakes the trailer is equipped with so the system can output correctly for the trailer's brake
system. Because the CCM/BSCM has to determine the type of trailer brake system that is being used, it can be
sensitive to a variety of trailer wiring issues.
The Trailer Brake Power Control Module K133 continuously sends a test pulse out on the trailer control circuit 47,
looking for a trailer that has been connected, and also to monitor for circuit faults. The way the test pulse reacts
when a trailer is connected is how the CCM/BSCM determines which type of braking system the trailer is equipped
with.
Even after the system detects the trailer, it will continue to send this test pulse on circuit 47, which now is monitoring
both the truck and trailer circuitry. Circuit 47 continues to be monitored for any faults so the driver can be notified of
any issues that may occur within the truck or trailer, as well as, to determine when the trailer is disconnected from
the truck. If the CCM/BSCM detects an issue, it will either display a "Check Trailer Wiring" or "Service Trailer Brake
System" message on the DIC. See DIC message/DIC below.
Electro-over Hydraulic Trailer Brakes
Electro-over hydraulic brake systems have some unique characteristics and here are a couple examples:
- The electro-over hydraulic brake pump motor needs a minimum duty cycle of approximately 20-30% to turn on the
pump motor. If the user gain is set too low, or if the driver lightly applies the brake pedal, the pump motor may not
turn on. This is normal. Pressing the brake pedal harder will help alleviate this concern. Always make sure trailer
brake gain has been adjusted according to the procedure shown in the owner’s manual.
- If the system detects electric-over-hydraulic brakes, when applying the brake pedal at 0 mph (stopped) there will be
no output from the truck's trailer brake system to the electro-over hydraulic pump motor. This is normal.
- Some electro-over hydraulic brake systems may need an adapter module, added to the trailer, so the vehicle
can recognize and function correctly with that system, see two examples below.
1). Certain Dexter Electric-over Hydraulic actuators (identified with TCV, TCB or CBH in the first (3) letters of the
serial number), were not designed to be compatible with the integrated trailer brake diagnostics. The integrated
trailer brake system will initially appear to function without issue; however, when the trailer brakes are applied, a
"Check Trailer Wiring" message will appear in the Driver Information Center. Then, after multiple brake applies, a
"Service Trailer Brakes" message will appear in the Driver Information Center, and trailer brakes will be disabled for
the remainder of the ignition cycle. The integrated trailer brake control system will report diagnostic trouble code
C1114. Dexter has released an Electric-over Hydraulic Compatibility Adapter (p/n K58-036-00), which can be
installed on the trailer, to correct this issue.
2). Hydrastar Electric/Hydraulic Trailer Brake Actuators on MY2014 and later full-size GM trucks, the Integrated
Trailer Brake Control System was designed to function with either electric, or electric/hydraulic brakes. In most
cases, Hydrastar electric/hydraulic trailer brake systems will operate on these vehicles without issue. In some
cases, the vehicle may have issues detecting the presence of the trailer's electric brake system, and the vehicle
integrated trailer brake control system will not operate. If this issue is observed, adding a Hydrastar Controller
Adapter Module 381-7073 to the trailer's brake system can help the vehicle detect the trailer brake system.
3). DTC C1114 setting when the truck is connected to a trailer equipped with a Hydrastar Electric/Hydraulic Trailer
Brake Actuators. For more information see the latest version of PIT6212 regarding a voltage spike from the
Hydrastar actuator causing the DTC C1114 to set.

Bulletin No.: PIT5509M

May, 2026

Page 3

Testing The Truck's Trailer Brake System
In many cases, trailer brake issues are the result of trailer wiring concerns and they are not related to the actual
vehicle's wiring. Most trailers with these wiring issues do not have high standards in relation to wiring/connections/
splices/routing practices (see examples in Step 3 below) when compared to similar automotive practices for wiring/
connections/splices/routing. Because of this, the CCM/BSCM can set faults, which can be hard to determine if they
are related to the truck or trailer. The easiest and fastest way to test the truck is to make a tester using trailer brake
magnets. This type of tester utilizes actual trailer brake magnets and will load the truck's electrical system, just like a
trailer would do without having to have the complete trailer. Shown below is an examples of such a tester. The
trailer brake system will operate with 1 to 4 pairs of trailer brake magnets (1 pair of magnets = 1 axle). It is
suggested to make a tester where the pairs of magnets can be added or removed to equal the same number of
brakes as the customer's trailer. Also, it is advised to make the harness long enough so it can be plugged into the
truck's 7 way connector and have the magnets placed into the bed of the truck. When the tester is connected to the
truck, the DIC will display "Trailer Connected" and GDS2 will show "Electro-magnetic" brakes in the CCM/BSCM
data parameter "Trailer Brake Type", refer to item 1 in "GDS2 Data" section below . If so, the vehicle can be driven
to see if any fault messages or DTCs set. If none occur with the tester installed, the truck is operating correctly and
the focus should be on the trailer wiring or 7 way connector.

4521885

Making the Tester
Parts needed:
1. 7 way RV trailer connector (example: Pollak Heavy Duty 7-Way Part # 12-706) Qty: 1
2. Electric Trailer Brake Magnets (example: Dexter Axle Part # K71-104-00) Qty: 2, 4, 6, or 8
3. 12 gauge wire and terminals/connectors Qty: as needed
Connect two 12 gauge wires to the 7-way RV trailer connector: one to the "Ground" terminal and a second to the
"Brake Controller Output" terminal (circuit 47), shown below. Connect the other ends of the 12 gauge wires to the
trailer brake magnets. All magnets must be connected in parallel so each magnet wire is connected to the Ground
and Brake Controller Output wires from the 7 way connector.
Note: Do NOT connect the magnets in series with each other.

4522121

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May, 2026

Bulletin No.: PIT5509M

4532066

In addition to the tester shown above, GM has recently released a new trailer simulator tool, P/N EL-52641, shown
below. When this tester is connected to the truck, the DIC will display "Trailer Connected" and GDS2 will show
"Electro-Hydraulic" brakes in the CCM/BSCM data parameter "Trailer Brake Type". If so, the vehicle can be driven to
see if any fault messages or DTCs set. If none occur with the tester installed, the truck is operating correctly and the
focus should be on the trailer wiring or 7 way connector.

5422063

If, after using either of the two tester shown above and the truck functions properly, you may follow the diagnostic
tips listed below to help diagnose a trailer related issue. Trailer issues are NOT covered under warranty, but this
information listed below can be used to help the customer/trailer supplier understand and correct any trailer related
issues if they so choose
DIC Message/ DTCs
It is important to understand and determine what message is being displayed, as well as, if DTC C1114 is setting.
This will help determine what type of fault to inspect for on the trailer. Below is the combinations of
message(s)/DTC to determine the type of fault the customer is experiencing:
- Check Trailer Wiring message with no DTC. This symptom is caused after the system detects a trailer and an
open and/or high resistance occurs in circuit 47/trailer brake output circuit, during the same ignition cycle.
Note: It is normal for the DIC to display "Check Trailer Wiring" when the trailer is disconnected from the truck while
the ignition is in the run position.
- Check Trailer Wiring message with DTC C1114 (NO Service Trailer Brake message). This symptom is caused by a
short to ground on circuit 47.
- Service Trailer Brake System with DTC C1114. This symptom is caused by a short to power on circuit 47 or a poor
trailer ground.

Bulletin No.: PIT5509M

May, 2026

Page 5

GDS2 Data
GDS2 (scan tool) can be used to view several different data parameters in the CCM/BSCM for the trailer brake
system. The Trailer Brake Type and Trailer Brake Control Output Circuit parameters listed below can be helpful to
make sure the CCM/BSCM is detecting the correct trailer brake system in addition to which type of fault it has
detected.
To view "Trailer Brake Type" build GDS2 as follows: CCM/BSCM->Data Display -> parameter "Trailer Brake Type":
"Electro-magnetic", "Electro-over hydraulic brakes", or "Undefined" (this is displayed with no trailer
connected). Example, shown below is a trailer equipped with electromagnetic trailer brakes.

4532060

To view "Trailer Brake Control Output Circuit" 47 faults, build GDS2 as follows: CCM/BSCM->Data Display ->
parameter "Trailer Brake Control Output Circuit": Okay, Short to Ground, Short to Power, or Unknown. Example,
shown below is a trailer with a short to ground on the trailer brake circuit.

4532428

1. Trailer Brake Type Parameter
When the trailer is connected, this parameter should be used to make sure the CCM/BSCM has detected the correct
type of trailer brakes. If the CCM/BSCM is detecting the wrong type of trailer brakes, here are several examples that
could cause this:
- Refer to the "Trailer Issues" section below items 4 and/or 5.
- A trailer equipped with electromagnetic brakes on only one axle (meaning there is only one pair of magnets) could
have a fault with one of the two magnets causing the CCM/BSCM to detect the wrong trailer brake type.
2. Trailer Brake Control Output Circuit Parameter
When the trailer is connected, this parameter can be used to help determine what type of fault the system has
detected on circuit 47, which could lie within the truck or trailer.
Sample Wiring Diagram
Below is an example of the truck's trailer brake system with the two main circuits that interface with the trailer brake
system circled.
Note: As always, use SI to look up the latest wiring diagrams for the vehicle being worked on.

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May, 2026

Bulletin No.: PIT5509M

4532064

Trailer Issues
1. The most likely reason for many of these issues is a poor/loose connection between the truck and trailer 7-way
connector.
- It is recommended to use a "Pollak HD" RV trailer connector, as shown in the latest version ofPIT5311. Pollak is
the OEM manufacturer of the truck's 7-way connector. By using a Pollak trailer connector, this will provide the best
connection possible.
- For Model Year 2014 to 2018 ONLY -Engineering has released an updated truck-side trailer connector that incorporates a stronger door/cover spring. This helps to ensure a secure connection between the trailer connector and the
truck connector. If the trailer connector is not being retained securely, replace the truck-side trailer connector with
the updated GM part number 23404450, which has the stronger door/cover spring.
2. Shown below is an example of a 5th wheel trailer where the trailer harness has been routed over the top of the
tailgate and plugged into the truck's bumper connector. While driving down the road, the trailer's wiring harness will
bounce up and down (A), causing the trailer's 7-way connector to lose connection (B) with the truck. The fix in this
case was to add the 5th wheel/camper wiring harness and route the 7-way connector's harness inside the box of the
truck, as shown (C).
Note: This same concern can also happen with bumper pull trailers if there is an excessive length of harness.
Securing the excessive trailer harness and installing the Pollak HD RV trailer connector per PIT5311 will help.

4514736

3. Poor trailer wiring connections, as shown below. General Motors does not recommend these type of connections, but many trailers utilize these connections. These type of connections are not robust and are not recommended, especially for brake wiring.

Bulletin No.: PIT5509M

May, 2026

Page 7

4514744

4514748

4. Trailer electronic sway control devices. Some trailers may be equipped with electronic sway control devices, like
the example shown below. These devices can apply the trailer’s brakes to control trailer sway. These trailer
mounted devices could potentially interfere with the functionality of the factory trailer brake controller resulting in
reduced trailer brake performance, or even loss of trailer brakes. Depending on the brand of the sway control device,
the following behaviors might be observed:
In some cases, when the trailer mounted sway module activates, it could cause the vehicle to set DTC C1114, and
display the “Service Trailer Brake System” message on the DIC. This could be an indication that the trailer brakes
are no longer functioning.
In other cases, when the trailer mounted sway module activates, the vehicle could display the “trailer disconnected”
message, indicating that trailer brakes are no longer available. Then, when the sway module ceases to activate, the
“trailer detected” message might be displayed which could indicate that the trailer brakes were available again.

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May, 2026

Bulletin No.: PIT5509M

Some trailer mounted sway control devices could also affect the vehicle’s ability to correctly differentiate between
electric or electric/hydraulic trailer brakes.
Before towing a trailer equipped with an electronic sway control device, the customer should contact the device's
manufacturer to be sure it is compatible with the GM vehicle.
Note: If a trailer sways this is likely caused by improper loading of the trailer, refer to the owners manual for more
information.

4514740

5. The CCM/BSCM is detecting the wrong type of trailer brakes. This is normally caused by an aftermarket device
wired into the trailer. The example shown below is an electric over hydraulic-to-electric brake adapter. These
adapters are used to make a truck that only works with electric trailer brakes work with a trailer that has electric over
hydraulic brakes.

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Bulletin No.: PIT5509M

May, 2026

Page 9

Parts Information
Description

Part Number

Qty

23404450

Truck 7-way
Trailer
Connector
Socket
(ONLY
2014-2018
Model Years)

1

Warranty Information
For vehicles repaired under the Bumper-to-Bumper coverage (Canada Base Warranty coverage), use the following
labor operation. Reference the Applicable Warranties section of Investigate Vehicle History (IVH) for coverage information.
Labor
Operation

Description

Labor Time

2460100

Wiring Harness Connector
Replacement - Trailer
Brake

Use
Published
Labor
Operation
Time

Version

1

Modified

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these
technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper
service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job
properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your
vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the
information.

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