C1114 on 2024-2026 GMC Sierra 2500: Trailer Brake System Faults, TSBs, and Fixes

What's Unique About the 2024-2026 Gmc SIERRA 2500

The late-model GMC Sierra HD trucks feature a highly sensitive and sophisticated trailer brake control system designed to work with various trailer brake types. This sensitivity, however, makes it prone to setting the C1114 code when it encounters electrical signals it doesn't expect. The issue is frequently not a fault with the truck itself, but an incompatibility with modern trailers that have their own power sources (solar, generators) or advanced braking systems (Electric-Over-Hydraulic) that can backfeed voltage or send confusing signals to the truck's control module.

Diagnostic Flowchart

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

Symptoms You May Notice

• "Service Trailer Brake System" message on the Driver Information Center (DIC).
• "Trailer Brake Disabled" message on the DIC.
• "Check Trailer Wiring" message on the DIC.
• No output from the integrated trailer brake controller.
• The trailer gain display on the DIC may disappear.

Most Likely Causes

1. Trailer with Onboard Battery/Charging System (Solar, Generator) 🔴 High Probability If a trailer's onboard battery (charged by solar, etc.) reaches a higher voltage than the truck's battery, it can backfeed voltage into the truck's Trailer Brake Power Module. The module interprets this as a 'false short to ground,' causing it to shut down and set C1114.
   How to confirm: The issue occurs specifically when towing a trailer equipped with a solar charger or other auxiliary power source, especially after the trailer battery has had time to fully charge. The issue may appear during an engine start/stop event.
   Typical fix: GM has issued Customer Satisfaction Program N232414840, which extends TSB #23-NA-149. This provides for a free replacement of the original trailer brake module with an updated part (P/N 85073615) to handle the voltage backfeed. This is covered at no charge until August 31, 2026, regardless of mileage or ownership.
   Est. part cost: $0 (Under Program N232414840) - $150
2. Trailer with Hydrastar Electric-Over-Hydraulic (EOH) Brakes 🔴 High Probability Certain Hydrastar EOH brake actuators can generate a voltage spike back into the truck's electrical system, particularly during light brake applications. The truck's sensitive control module interprets this spike as a fault and sets C1114.
   How to confirm: The code appears only when towing a trailer with a Hydrastar EOH system. Per TSB PIT6212D, a dealer can use a Trailer Simulator Tool (P/N EL-52641) to confirm the truck's system is working correctly, isolating the fault to the trailer.
   Typical fix: This is a trailer-side issue. Per TSB #PIT6212D, no repairs should be made to the truck. The trailer needs to be inspected by a trailer repair shop. Hydrastar is reportedly aware of the issue and may have a solution or adapter available, such as the Controller Adapter Module HBA-CAM (381-7073).
   Est. part cost: $0 (for truck diagnosis) - $200+ (for trailer modification)
3. Poor Connection at 7-Way Connector 🟡 Medium Probability Even minor corrosion, spread pins, or a loose-fitting plug can cause intermittent signal loss. The truck's system continuously monitors the connection and will interpret a poor connection as a fault.
   How to confirm: Visually inspect both the truck-side and trailer-side 7-way connectors for green/white corrosion, bent pins, or damage. Wiggling the connector while connected may trigger the fault message.
   Typical fix: Thoroughly clean both connectors. If the trailer-side plug is low quality, replace it with a high-quality, sealed unit. TSBs specifically recommend the Pollak brand as they are the OEM manufacturer for the truck's socket, ensuring the best possible connection.
   Est. part cost: $15 - $120
4. Trailer Wiring Fault (Poor Ground, Short Circuit) 🟡 Medium Probability Many trailers have lower-quality wiring and connections that are susceptible to corrosion and damage. The Sierra's sensitive system will detect these faults, which older trucks might have ignored.
   How to confirm: Test the truck with a known-good trailer. If the code disappears, the fault is in the original trailer's wiring. The specific DIC message can help: 'Check Trailer Wiring' often points to a short-to-ground, while 'Service Trailer Brake System' can indicate a short-to-power or a bad ground.
   Typical fix: Inspect and repair the trailer's wiring harness, paying close attention to the ground wire (typically white) and the brake output wire (typically blue, Circuit 47). Repair any corroded or non-robust connections.
   Est. part cost: $5 - $50

Rare But Worth Checking

• Aftermarket Trailer Electronic Sway Control: Some aftermarket trailer-mounted sway control devices can interfere with the truck's integrated brake controller, applying the brakes independently and causing the truck to set a C1114 code.

Diagnosis Steps

1. Confirm DTC C1114 is present in the Chassis Control Module using a scan tool.
2. Note the exact message on the DIC. Per TSB PIT5509, 'Check Trailer Wiring' often indicates a short-to-ground on Circuit 47, while 'Service Trailer Brake System' suggests a short-to-power or a poor trailer ground.
3. Identify the type of trailer connected. Does it have Electric-Over-Hydraulic (EOH) brakes? Does it have a solar panel, generator, or auxiliary battery?
4. If a trailer is connected, disconnect it and clear the codes. If the code does not return, the fault is almost certainly on the trailer side.
5. Test the truck with a known-good trailer or a dedicated trailer simulator tool (like GM's EL-52641) to confirm the truck's system is functioning correctly.
6. If the issue is present with a trailer having a battery/solar charger, consult a GM dealer about Customer Satisfaction Program N232414840, which provides a no-cost replacement of the trailer brake module until August 31, 2026.
7. If the issue is present with a Hydrastar EOH trailer, consult a trailer repair facility per TSB #PIT6212D. Do not perform repairs on the truck.
8. Thoroughly inspect the 7-way connectors on both the truck and trailer for corrosion, damage, or loose pins.
9. If no trailer-specific cause is identified, inspect the trailer wiring harness for damage, paying special attention to the ground and brake output circuits.

Parts You'll Likely Need

• Trailer Brake Power Module (OEM #85073615) — This is the updated module specified in TSB #23-NA-149 and Customer Satisfaction Program N232414840 to correct issues with voltage backfeed. It is located above the spare tire. This part supersedes older numbers like 23306694.
  Trusted brands: ACDelco, GM Genuine Parts
  OEM price range: $100-$150
  Aftermarket price range: N/A
• Trailer-Side 7-Way Connector Plug — A high-quality, sealed trailer plug provides a robust connection that the truck's sensitive system requires. GM TSBs recommend the Pollak brand because Pollak is the OEM supplier for the truck's socket, ensuring the best fit.
  Trusted brands: Pollak (12-706), Hopkins
  OEM price range: $25-$40
  Aftermarket price range: $15-$30

Technical Service Bulletins (TSBs) & Recalls

• N232414840: A Customer Satisfaction Program (not a TSB, but related) that provides a free fix for the C1114 code when caused by voltage feedback from a trailer's charging system. Expires Aug 31, 2026.
• 23-NA-149: The technical bulletin detailing the cause (voltage backfeed from trailer battery/solar) and correction (replace trailer brake module with updated part) for the C1114 code.
• PIT6212D: Addresses C1114 caused by a voltage spike from Hydrastar Electric Over Hydraulic trailer brakes. Explicitly states this is a trailer-side issue and not to repair the truck.
• PIT5509J/K/L: A comprehensive diagnostic guide for C1114. Crucially, it helps differentiate the fault based on the DIC message: 'Check Trailer Wiring' for a short-to-ground, and 'Service Trailer Brake System' for a short-to-power or poor ground.
• 21-NA-155: Recommends using high-quality Pollak brand trailer-side plugs and provides a part number for an updated truck-side 7-way socket if terminals are worn.

Platform-Specific Known Issues

• Customer Satisfaction Program N232414840: GM issued this program for 2024 Sierra/Silverado HD models to address C1114 caused by trailer battery voltage feedback. The program directs dealers to replace the Trailer Brake Power Module with an updated part (85073615) at no charge to the customer. This program is in effect until August 31, 2026, regardless of vehicle mileage, age, or ownership.

Mechanic-Grade Diagnostic Values

• TBCM Relay Feedback Signal Voltage — expected: 3.2 - 4.1 V (with ignition ON, trailer disconnected). Failure: A voltage higher than 4.1V suggests a short to voltage; a voltage lower than 3.2V suggests a short to ground or an open/high resistance.
• Trailer Brake Control Relay Ground Circuit Resistance — expected: Less than 5.0 ohms (measured between the module's ground circuit terminal and a clean chassis ground). Failure: Resistance greater than 5.0 ohms indicates an open or high resistance in the ground circuit.

Hidden / Shadow Codes Worth Checking

• C1114 + 'Check Trailer Wiring' Message: This combination indicates the Chassis Control Module has detected a short to ground on the trailer brake output circuit (Circuit 47). (see via Visible on the Driver Information Center (DIC) and can be confirmed with a GDS2 scan tool.)
• C1114 + 'Service Trailer Brake System' Message: This combination 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 Visible on the Driver Information Center (DIC) and can be confirmed with a GDS2 scan tool.)
• U0137: Lost Communication With Trailer Brake Control Module. This code may be stored in other modules (like ABS) when the Trailer Brake Control Module (K170) is malfunctioning or has lost power or ground. (see via Professional scan tool (like GDS2) in the ABS or BCM modules.)

Scan Tool Commands That Help

• GDS2: Chassis Control Module -> Data Display -> 'Trailer Brake Control Output Circuit' — This is a primary diagnostic parameter. It directly displays the fault status detected by the module, such as 'Okay', 'Short to Ground', or 'Short to Power', which immediately guides the electrical diagnosis.
• GDS2: Chassis Control Module -> Data Display -> 'Trailer Brake Type' — Use this to verify if the truck correctly identifies the connected trailer’s brake system ('Electro-magnetic' or 'Electro-over hydraulic'). If it shows 'Undefined' with a trailer connected, it points to a connection or trailer wiring fault.
• GDS2: Trailer Brake Control Module -> Data Display -> 'TBCM Relay Feedback Signal' — Use this to monitor the voltage on the brake output circuit in real-time. It is especially useful for diagnosing intermittent shorts or confirming the voltage specification (3.2-4.1V) is being met.

Wiring & Ground Locations

• K170 Trailer Brake Control Module — Located above the spare tire, mounted to a bracket that may also hold the fuel pump control module.. This is the module that sets the code. It is the target for replacement under Customer Satisfaction Program N232414840 and is susceptible to water intrusion.
• Circuit 47 — A Dark Blue wire that runs from the K170 Trailer Brake Control Module to pin 2 of the 7-way trailer connector at the bumper.. This is the specific trailer brake output circuit that is monitored for faults. All C1114 faults (short to ground, short to power, open) occur on this circuit.
• G401 — A chassis ground point associated with the rear trailer connector wiring harness.. A poor connection at this ground can cause a 'Service Trailer Brake System' message with code C1114, as the system can interpret the high resistance as a circuit fault.

Real Owner Repair Stories

• YouTube user 'GMC and Chevrolet Trailer Brakes Not Working Fix.' (2024 Chevrolet 2500HD (sister vehicle)) — Picked up a new travel trailer and immediately got a 'Check trailer wiring' message on the DIC. The trailer brake icon in the infotainment screen was not illuminated, indicating no connection.
  ❌ Tried (didn't work) Visual inspection of truck and trailer wiring., Replacing the 7-pin connector on the trailer.
  ✅ What actually fixed it The root cause was interference from the trailer's solar charge controller back-feeding voltage. The temporary roadside fix was to disconnect the wires from the solar panel. The permanent fix was installing an inline switch on the solar panel circuit to disable it before towing, which immediately resolved the error and restored trailer brake function.

OEM Part Supersession History

• e.g., 23306694 → 85073615 — The new module is designed to handle voltage feedback from trailer-side charging systems without setting a fault code.
  Heads up: Using an older module on a truck that tows a trailer with a solar/battery system will likely result in a C1114 code.
• Unknown → 84056018 — This is an updated truck-side 7-way trailer connector socket to replace the original if its terminals are found to be deformed or have excessive wear.