C1114 on 2015-2022 GMC Sierra 1500: Trailer Brake System Fault Guide

What's Unique About the 2015-2022 Gmc SIERRA 1500

These GM trucks feature a sophisticated integrated trailer brake control (ITBC) system that actively monitors the trailer connection. The system continuously sends a test pulse out on circuit 47 to determine the type of trailer brakes and check for faults. This sensitivity makes it prone to setting the C1114 code due to common, and often poor, trailer-side wiring, non-SAE compliant connectors, or aftermarket accessories that don't meet OEM standards. The issue is so frequent that GM has issued multiple, evolving Technical Service Bulletins (like PIT5509) focusing almost entirely on diagnosing trailer-side problems rather than truck-side component failures.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Generation note: This issue affects both the third generation (K2XX; 2015-2018) and fourth generation (T1XX; 2019-2022) of the GMC Sierra 1500. The diagnostic approach is similar for both, as confirmed by TSBs covering the entire year range. The K2XX models (2014-2018) are specifically called out for an updated truck-side connector with a stronger spring.

Symptoms You May Notice

• "Service Trailer Brake System" message on the Driver Information Center (DIC).
• "Check Trailer Wiring" message on the DIC.
• Integrated trailer brake controller is disabled or functions intermittently.
• No power output to the trailer brakes.
• Trailer brake gain display on DIC shows "--" or is unresponsive.
• With a trailer connected, the trailer icon on the dash may flash or not appear at all.

Most Likely Causes

1. Poor Connection at 7-Pin Connector 🔴 High Probability The truck's connector spring can weaken, or the trailer-side plug may be out-of-spec (non-SAE compliant), causing a loose connection that creates intermittent opens or shorts. Corrosion inside either connector is also a very common culprit.
   How to confirm: Wiggle the trailer connector while it's plugged in to see if the error message appears or disappears. Visually inspect the pins on both the truck and trailer for corrosion (green or white powder), damage, or recessed pins. Apply dielectric grease to the contacts.
   Typical fix: For 2014-2018 models, GM recommends an updated truck-side connector (Part #23404450) with a stronger spring. 🎬 Watch: How to replace the updated truck-side connector For all years, using a high-quality, SAE-compliant trailer-side plug, like a Pollak HD (Part #12-706), is highly recommended by GM TSBs. Cleaning terminals with a contact cleaner is a primary step.
   Est. part cost: $15-$60
2. Faulty or Poor-Quality Trailer Wiring 🔴 High Probability The truck's sensitive monitoring system easily detects issues common in trailers, such as insufficient grounding, poor-quality splices (twist caps, non-weatherproof butt connectors), or damaged wires.
   How to confirm: Test the truck with a known-good trailer or a dedicated trailer brake tester (like one made with actual brake magnets). If the code does not return, the fault is in the trailer. Inspect the trailer's main ground wire (usually white) for a clean, tight connection to the trailer frame.
   Typical fix: Repair the trailer's wiring. This often involves cleaning and securing the main ground connection to the trailer frame and replacing any low-quality splices with soldered, heat-shrunk connections. Ensure the trailer harness has proper strain relief and is not dangling, which can cause intermittent disconnects.
   Est. part cost: $5-$50
3. Incompatible Aftermarket Trailer Devices 🟡 Medium Probability The CCM can misinterpret signals from aftermarket electronic sway control devices, some electric-over-hydraulic (EOH) adapters, or even trailer-mounted solar charge controllers, causing a fault.
   How to confirm: If the trailer is equipped with such a device, temporarily disconnect it to see if the code clears. Some specific EOH systems, like Hydrastar, are known to cause issues like voltage spikes without a specific compatibility adapter. A trailer battery with a higher state of charge than the truck (often due to solar) can also backfeed voltage and trigger a fault.
   Typical fix: Install a manufacturer-recommended compatibility adapter (e.g., Hydrastar part #HBA-CAM). For solar-related issues, installing a switch or diode to prevent back-feeding from the trailer battery to the truck may be necessary. For some 2020-2024 models, a recall (N232414840) was issued to replace the Trailer Brake Power Module to address this back-feeding issue.
   Est. part cost: $50-$150
4. Short or Open in Trailer Brake Output Circuit ⚪ Low Probability While less common than trailer issues, a fault can occur in the truck's wiring (Circuit 47, typically a dark blue wire) between the Chassis Control Module and the 7-pin connector, often due to chafing on the frame or corrosion.
   How to confirm: With the trailer disconnected, use a multimeter to check for shorts to ground, shorts to power, or high resistance on the trailer brake control circuit at the 7-pin connector. A scan tool can specify the fault type (short to ground, short to power, open).
   Typical fix: Trace the faulty circuit (Circuit 47) from the 7-pin connector along the frame rail towards the front of the vehicle and repair the damaged wiring or connector.
   Est. part cost: $1-$20

Rare But Worth Checking

• Faulty Chassis Control Module (CCM) / Brake System Control Module (BSCM): This is extremely rare and should only be considered after all other possibilities, especially trailer-side issues, have been exhaustively ruled out with proper diagnostic tools like a trailer simulator (GM tool P/N EL-52641).
• Blown Fuse for Trailer Brake System: A blown fuse in the under-hood fuse block can disable the system. This is often a symptom of a short circuit in the trailer wiring, not the root cause. Check fuses labeled for trailer brakes or trailer battery.
• Faulty In-Dash Trailer Brake Controller Switch: While uncommon for causing C1114 specifically, a faulty switch is a known issue on these trucks and can cause the 'Service Trailer Brake System' message, though often without a specific DTC. It's a relatively cheap and easy part to replace.
• Parking Brake Actuator Failure: A single owner complaint (NHTSA ODI #11710153) linked C1114 to a parking brake actuator. This is not corroborated by TSBs or service data and is likely an outlier or a situation involving multiple simultaneous faults.

Diagnosis Steps

1. Check for the "Service Trailer Brake System" or "Check Trailer Wiring" message on the DIC. This confirms an active fault.
2. If a trailer is connected, disconnect it. Cycle the ignition. If the message disappears, the fault is almost certainly with the trailer.
3. Thoroughly inspect the 7-pin connectors on both the truck and trailer. Look for corrosion, bent/recessed pins, and debris. Ensure a snug fit. Clean both sides with electrical contact cleaner and apply dielectric grease.
4. If possible, connect the truck to a different, known-good trailer or a trailer simulator tool (GM P/N EL-52641). If the code does not return, the problem is confirmed to be with the original trailer.
5. On the original trailer, inspect the wiring. Start with the main ground wire (usually white) at the 7-pin plug and where it attaches to the trailer frame. Ensure the connection is clean, tight, and free of corrosion.
6. Follow the trailer's brake wiring (blue wire), looking for any damage, frayed wires, or poor-quality splices (e.g., Scotch-Loks or twist caps). Replace with soldered, heat-shrunk connections.
7. If the trailer has aftermarket accessories like a solar charger or EOH brakes, temporarily disable them to see if the fault clears.
8. If a truck-side fault is suspected, use a scan tool to read the specific fault type (Short to Ground, Short to Power, or Open) for DTC C1114. This will guide testing of the truck's harness (Circuit 47).
9. Check relevant fuses in the under-hood fuse block related to trailer braking.

Parts You'll Likely Need

• Truck-Side 7-Pin Trailer Connector (OEM #23404450) — For 2014-2018 models, the original connector's spring can weaken, leading to a poor connection. This updated part has a stronger spring to hold the trailer plug more securely. It supersedes part #22799842.
  Trusted brands: ACDelco, GM Genuine Parts
  OEM price range: $40-$60
  Aftermarket price range: $25-$45
• Trailer-Side 7-Pin Connector Plug — Many trailer-side plugs are low quality and do not meet SAE specifications, causing intermittent connection issues. Replacing a worn or cheap plug with a quality unit is a common fix. GM TSBs specifically recommend the Pollak HD 7-Way Plug (e.g., Part #12-706).
  Trusted brands: Pollak, Hopkins
  Aftermarket price range: $15-$30
• Trailer Brake Control Module (OEM #85073615) — This part is rarely the cause of the fault and should only be replaced after all wiring and trailer issues have been ruled out. It is often misdiagnosed. Requires programming. A recall (N232414840) for some 2020-2024 models involves replacing this module to fix issues with voltage back-feeding from trailer batteries.
  Trusted brands: ACDelco, GM Genuine Parts
  OEM price range: $80-$120
  Aftermarket price range: $50-$90

Related Codes That Often Appear With This One

• C1112 — This code indicates a fault in the trailer brake control relay circuit and can appear alongside C1114 when there are complex electrical issues in the trailer brake system.
• C1119 — This code points to a fault in the trailer brake control relay feedback circuit and may be set with C1114 if the control module detects inconsistencies in the relay's operation.

Technical Service Bulletins (TSBs) & Recalls

• PIT5509L (Aug 2024): The latest version of a long-running diagnostic guide for C1114, emphasizing trailer-side issues, connector quality, and the use of diagnostic testers.
• PIT6212A (Aug 2024): Specifically addresses C1114 caused by voltage spikes from Hydrastar brand electro-hydraulic brake actuators and advises testing the truck with a simulator before attempting any truck-side repairs.
• PIT5311F (Oct 2016): Details issues with intermittent trailer brake messages caused by insufficient trailer grounding or poor 7-way connector contact, recommending part #23404450 for the truck-side connector.
• Recall N232414840: For certain 2020-2024 HD trucks, this recall replaces the Trailer Brake Power Module to prevent faults caused by voltage back-feeding from a trailer with a higher battery charge (e.g., from a solar panel).

Platform-Specific Known Issues

• {'title': 'The Trailer Ground Wire is the #1 Culprit', 'description': 'Across numerous forums and TSBs, the most common real-world fix is addressing a poor ground connection on the trailer. This is usually the white wire. Owners report that even if the ground looks okay, removing it, cleaning the contact point on the trailer frame to bare metal, and re-securing it often resolves the C1114 code instantly.'}
• {'title': 'Fifth-Wheel Harness Routing', 'description': 'TSB PIT5509 points out a specific issue with fifth-wheel trailers where the harness is draped over the tailgate. The bouncing and movement can cause an intermittent connection at the bumper plug. The official fix is to install a dedicated in-bed 7-pin connector and secure the harness properly.'}
• {'title': 'Hydrastar EOH Actuator Incompatibility', 'description': 'TSB PIT6212 specifically calls out the Hydrastar brand of electro-hydraulic actuators for causing voltage spikes that trigger C1114. Owners confirm that installing the Hydrastar Adapter Module (HBA-CAM) is often necessary to resolve the communication error between the truck and this specific brake system.'}

Mechanic-Grade Diagnostic Values

• Resistance of a single trailer brake magnet assembly — expected: 3.0 to 4.0 Ohms (when measured cold). Failure: A reading of 'O.L.' indicates an open circuit/bad magnet. A reading significantly outside the range indicates a faulty magnet.
• Total resistance of all trailer brakes at the 7-pin connector — expected: 0.75 to 1.5 Ohms for a typical tandem axle (4 brakes) trailer. The magnets are wired in parallel, so the total resistance will be the resistance of one magnet divided by the number of magnets (e.g., 3.2 Ohms / 4 magnets = 0.8 Ohms).. Failure: A higher resistance indicates one or more faulty magnets or a wiring issue. For example, with 4-ohm magnets, a reading of 2.0 ohms would indicate only two of the four magnets are working.
• TBCM Relay Feedback Signal Voltage (K2XX models) — expected: 3.2 to 4.1 Volts between terminal C (tan wire) and ground at the trailer brake relay plug.. Failure: A reading outside this range when the fault is active can indicate a faulty Trailer Brake Control Module (TBCM), assuming the circuit itself tests normal for shorts.

Hidden / Shadow Codes Worth Checking

• C1114 with 'Check Trailer Wiring' message: Indicates the Chassis Control Module has detected a short to ground on the trailer brake output circuit (Circuit 47). (see via This is a combination of the DTC read by a standard scanner and the specific message displayed on the Driver Information Center (DIC).)
• C1114 with 'Service Trailer Brake System' message: Indicates the Chassis Control Module has detected a short to power on the trailer brake output circuit (Circuit 47) or a poor trailer ground connection. (see via This is a combination of the DTC read by a standard scanner and the specific message displayed on the Driver Information Center (DIC).)
• GDS2 Parameter: 'Trailer Brake Control Output Circuit': This is not a code, but a live data parameter that provides a specific fault status. It will read 'Okay', 'Short to Ground', 'Short to Power', or 'Unknown'. This is the most precise way to identify the fault type. (see via Using a GM GDS2 scan tool, navigate to Chassis Control Module -> Data Display -> 'Trailer Brake Control Output Circuit'.)

Scan Tool Commands That Help

• GDS2: Data Display: 'Trailer Brake Type' — Use this to verify what type of brake system the truck thinks is connected ('Electro-magnetic', 'Electro-over hydraulic', or 'Undefined'). This is critical for diagnosing compatibility issues, especially when using the GM trailer simulator tool EL-52641.
• GM Special Tool EL-52641: Trailer Presence Simulator Tester — This is the definitive tool to determine if the fault is in the truck or the trailer. If the C1114 code does not set while this simulator is connected, the truck's system is functioning correctly, and the fault lies with the trailer.

Wiring & Ground Locations

• Trailer Brake Control Module (T1XX) — On 2019-2022 models, the module is located above the spare tire, mounted to a bracket, often next to an auxiliary chassis control module.. This module is the brain of the system on newer trucks. It is susceptible to water intrusion from road spray, which can corrode the internal circuit board and cause C1114 and communication faults.
• G401 — Frame ground, typically located on the driver's side frame rail near the rear of the vehicle.. A TSB for earlier models specifically calls out checking this ground. A poor ground connection here can cause a variety of trailer-related electrical faults, including C1114.
• Trailer Brake Controller Power Wires (K2XX) — For trucks without a factory controller, the power wires are typically blunt-cut and taped to a harness near the under-hood power distribution box/fuse block.. When installing an aftermarket controller, these connections must be made correctly. A poor connection here can lead to no power for the controller and associated faults.
• TBCM Connector Pins (T1XX) — At the connector for the module above the spare tire on 2019+ models.. Pin 1 is power, Pin 9 is ground, and Pin 12 is the LIN communication wire. These can be tested for voltage and continuity when diagnosing a suspected faulty module.

Real Owner Repair Stories

• YouTube Channel 'Water Damaged Trailer Brake Control Module' (2019 GMC Sierra Elevation) — 'Service Trailer Brake System' message on every startup. Code U1556 (lost communication with power brake control module) was also present.
  ❌ Tried (didn't work) Visual inspection of external wiring and connectors, which all appeared clean and undamaged. Power and ground tests at the module connector were good.
  ✅ What actually fixed it The Trailer Brake Control Module (located above the spare tire) was replaced. Upon dissecting the old module, it was found to be full of salty water and the internal circuit board was heavily corroded. The water ingress was suspected to be from a compromised seal on the module's connector.

"I Checked Everything" — The Actual Cause

• In one documented case on a 2019 Sierra, all external wiring, power, and ground tests passed inspection. The root cause was not a wiring fault but water that had seeped inside the Trailer Brake Control Module itself, corroding the internal electronics. This type of failure is impossible to detect with external wiring tests alone and required replacing the module.

OEM Part Supersession History

• Varies by year → 23404450 — Updated truck-side 7-pin receptacle with a stronger spring to ensure a more robust connection.
• Unknown → 85073617 — Standard part number for the Trailer Brake Control Module on later K2XX models (e.g., 2018).
  Heads up: Part numbers are specific to model year ranges and platform (K2XX vs T1XX). Always verify with VIN.

Model Year Variations Within This Range

• 2019-2022 (T1XX Platform): The Trailer Brake Control Module is a distinct, separate module located above the spare tire. Additionally, if the truck was not built with the integrated trailer brake controller (RPO JL1), the factory system cannot be added later via software. An aftermarket controller must be wired in.
• 2015-2018 (K2XX Platform): The trailer brake control functions are more integrated into other control modules. The system is known for having a weaker 7-pin connector spring, leading GM to recommend an updated part (23404450).