C1114 on 2019-2023 Chevy Silverado 2500: Service Trailer Brake System Causes and Fixes

What's Unique About the 2019-2023 Chevrolet SILVERADO 2500

The integrated trailer brake control system on these modern Silverado HD trucks is sophisticated, designed to work with both standard electric and electric-over-hydraulic (EOH) trailer brakes. This requires the truck's Chassis Control Module (CCM) or Brake System Control Module (BSCM), depending on the year, to actively identify the trailer type upon connection by analyzing the reaction to a test pulse. This sensitivity makes the system prone to setting faults like C1114 due to issues not just on the truck, but also with trailer wiring, aftermarket trailer accessories, or even a poor connection at the 7-pin plug. GM has issued extensive technical service bulletins (like the PIT5509 series) acknowledging that diagnosing these issues can be complex because the fault could lie with either the truck or the trailer, and that many trailer wiring systems are not built to robust automotive standards. A specific issue noted in a GM Customer Satisfaction Program for 2020 and 2024 models is that voltage feedback from a trailer's own battery can create a false short-to-ground signal, disabling the system.

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)
• "Check Trailer Wiring" message on the DIC
• Trailer brakes do not engage or engage erratically
• Integrated trailer brake controller is disabled or shows an error
• "Trailer Connected" message appears and disappears intermittently
• Trailer lights may stay on or function incorrectly.

Most Likely Causes

1. Trailer Wiring or Connector Issues 🔴 High Probability The system is sensitive to faults, and trailer wiring is often less robust than vehicle wiring. Corrosion, loose pins, poor grounds, and non-standard wiring splices are extremely common and are the most frequent cause of C1114.
   How to confirm: The primary diagnostic step is to test the truck with a different, known-good trailer or a dedicated trailer brake system tester (like GM tool EL-52641) as recommended by GM. If the code does not return, the fault is in the trailer's wiring. Inspect the trailer's 7-pin plug for corrosion, bent pins, or moisture. Also inspect the trailer's ground wire (usually white) and its connection to the trailer frame.
   Typical fix: Repair the wiring on the trailer. This may involve replacing the 7-pin plug on the trailer, fixing shorted or open wires, or cleaning and securing ground connections. Using a high-quality, SAE-compliant trailer-side connector, like those from Pollak (the OEM supplier), is highly recommended by GM TSBs to ensure a secure connection.
   Est. part cost: $20-$50
2. Truck-Side Wiring or 7-Pin Connector Fault 🟡 Medium Probability The rear connector is exposed to the elements, leading to potential corrosion or damage. The spring-loaded door can weaken, causing a loose connection. The wiring harness leading to the connector can also be damaged or suffer from water intrusion into the connectors for the Trailer Brake Power Module (TBPM), located above the spare tire.
   How to confirm: If the code appears with a known-good trailer or a tester, the issue is on the truck. Visually inspect the truck's 7-pin connector for corrosion, spread terminals, or a weak door. Check for a short to power or ground on the trailer brake output circuit (circuit 47, dark blue wire) as indicated by the TSB. Inspect the Trailer Brake Power Module (K133) and its connector, often located near the spare tire, for missing or unseated cavity plugs which can allow water entry.
   Typical fix: Clean or replace the truck-side 7-pin connector socket. GM released an updated part (23404450) with a stronger spring to hold the trailer plug more securely. Repair any damaged wires in the harness and ensure all module connectors are clean, dry, and fully seated. Applying dielectric grease can help prevent future corrosion.
   Est. part cost: $30-$100
3. Incompatible Trailer Equipment ⚪ Low Probability The CCM/BSCM can misinterpret signals from certain aftermarket trailer devices, such as electronic sway control systems or non-standard electric-over-hydraulic (EOH) brake adapters. These devices can interfere with the truck's diagnostic pulses.
   How to confirm: The code appears only with a specific trailer that has aftermarket electronic accessories. Disconnecting these accessories may resolve the issue. Some EOH brake systems, like certain Dexter models, are known to be incompatible without a specific adapter.
   Typical fix: Remove the incompatible aftermarket device or install a manufacturer-recommended compatibility adapter. For example, Dexter offers P/N K58-036-00 for some of their EOH systems to resolve this specific issue.
   Est. part cost: $50-$200
4. Chassis Control Module (CCM) Fault ⚪ Low Probability While less common than wiring issues, electronic modules can fail. GM notes that many modules are replaced unnecessarily when the actual fault is in the wiring or connectors. For 2020 and 2024 models, a specific condition where voltage feedback from the trailer's battery creates a false short requires replacing the Trailer Brake Power Module (TBPM), not the main CCM/BSCM.
   How to confirm: This is typically a process of elimination. If all truck-side wiring, trailer wiring, and connectors have been verified as good using a dedicated tester, the CCM itself may be the problem. A dealer-level scan tool (GDS2) can monitor CCM data parameters like 'Trailer Brake Control Output Circuit' status to help diagnose the module.
   Typical fix: Replace and program the Chassis Control Module. This must be done by a qualified shop or dealership with the proper programming tools.
   Est. part cost: $300-$600

Rare But Worth Checking

• Faulty In-Dash Trailer Brake Controller Switch:
• Voltage Feedback from Trailer Battery (2020 & 2024 models):

Diagnosis Steps

1. Connect a scan tool and confirm the presence of code C1114 in the Chassis Control Module (CCM) or Brake System Control Module (BSCM). Note whether the accompanying DIC message is "Service Trailer Brake System" or "Check Trailer Wiring".
2. If a trailer is connected, disconnect it. Clear the codes. The code should not set without a trailer connected. If it does, a truck-side wiring fault is highly likely.
3. Connect a known-good trailer or a dedicated trailer brake system tester tool (like GM tool EL-52641). If the code does NOT return, the fault lies within the original trailer's wiring, plug, or brake components.
4. If the code DOES return with a known-good trailer/tester, the fault is on the truck.
5. Thoroughly inspect the truck's 7-pin connector for any signs of corrosion, moisture, or damaged/bent pins. Ensure the door spring is strong. Replace with OEM part 23404450 if weak or damaged.
6. Inspect the wiring harness from the 7-pin connector to the Trailer Brake Power Module (K133), which is located above the spare tire. Look for any chafed, broken, or corroded wires and check for water intrusion in the connectors.
7. Using a GDS2 scan tool, monitor the 'Trailer Brake Control Output Circuit' parameter. This will help identify the specific fault type ('Short to Ground', 'Short to Power', 'Okay').
8. Following TSB guidelines, check the trailer brake output circuit (dark blue wire, circuit 47) for a short to power or a short to ground, which are common triggers for C1114.
9. If the vehicle is a 2020 or 2024 model and all else fails, investigate GM Customer Satisfaction Program N232414840, which addresses false shorts caused by trailer battery voltage feedback, fixed by replacing the Trailer Brake Power Module.
10. If all wiring and connections are confirmed to be good, the Chassis Control Module (CCM) or Brake System Control Module (BSCM) may be faulty. This requires advanced diagnostics to confirm before replacement.

Parts You'll Likely Need

• 7-Pin Trailer Connector Socket (Truck-Side) (OEM #23404450) — The truck's connector is a frequent point of failure due to corrosion and a weak door spring causing a poor connection. This updated part has a stronger spring to hold the trailer plug securely. This part number replaces the older 22799842.
  Trusted brands: ACDelco, Pollak
• Trailer Brake Power Module (TBPM) (OEM #85073615) — For 2020 and 2024 models, this updated module is the specific fix for a known issue where voltage feedback from a trailer battery can cause a false short-to-ground condition, triggering code C1114.
  Trusted brands: ACDelco, GM Genuine Parts

Related Codes That Often Appear With This One

• U0137 - Lost Communication With Trailer Brake Control Module

Technical Service Bulletins (TSBs) & Recalls

• PIT5509K: The most current version of a long-running TSB. Provides comprehensive diagnostic advice for 'Check Trailer Wiring' and 'Service Trailer Brake System' messages with DTC C1114, emphasizing that the issue could be the truck or the trailer and detailing how to build a tester to differentiate.
• PIT5311F: Specifically calls out poor connections at the 7-way connector and insufficient trailer grounding as primary causes. Recommends using a Pollak HD trailer-side plug and replacing the truck-side socket with part 23404450 if worn.
• PIT5529: Addresses water intrusion into the Trailer Brake Power Module (K133) connector due to missing or unseated cavity plugs, which can cause various trailer brake DTCs including C1114.

Platform-Specific Known Issues

• Per TSB PIT5509K, the diagnosis of this code is highly dependent on whether the accompanying message is 'Check Trailer Wiring' (short to ground on circuit 47) or 'Service Trailer Brake System' (short to power on circuit 47 or poor trailer ground).
• For 2019-2020 models specifically, the CCM/BSCM does not distinguish between electromagnetic and EOH brakes in the scan tool data; both will show as 'electromagnetic'. This is normal for those years.
• Some owners report that the issue can be triggered after the truck is stopped and then accelerates, pointing to an intermittent connection that is affected by vehicle movement.
• GM has Customer Satisfaction Programs (e.g., N232414840) for some model years related to trailer brake issues caused by voltage feedback from the trailer's battery, which can also trigger faults.

Mechanic-Grade Diagnostic Values

• Trailer Brake Magnet Resistance (per magnet) — expected: 3.0-3.8 Ohms. Failure: Significantly higher (open) or lower (shorted) resistance. A single faulty magnet on a single-axle trailer can cause the system to misidentify the trailer type and set a fault.
• Trailer Brake Output Circuit (Circuit 47) status — expected: Okay. Failure: Scan tool showing 'Short to Ground' or 'Short to Power'.

Hidden / Shadow Codes Worth Checking

• C1114 + 'Service Trailer Brake System' message: Indicates a short to power on the trailer brake output circuit (47) or a poor trailer ground connection. (see via Visible on the Driver Information Center (DIC) in conjunction with scanning the code.)
• C1114 + 'Check Trailer Wiring' message: Indicates a short to ground on the trailer brake output circuit (47). (see via Visible on the Driver Information Center (DIC) in conjunction with scanning the code.)

Scan Tool Commands That Help

• GDS2: Data Display -> 'Trailer Brake Type' — Use this to verify if the truck is correctly identifying the connected trailer as 'Electro-magnetic' or if it's 'Undefined'. An incorrect reading points to a connection or trailer wiring issue.
• GDS2: Data Display -> 'Trailer Brake Control Output Circuit' — This is the most critical diagnostic parameter. It directly tells the technician if the module has detected a 'Short to Ground', 'Short to Power', or 'Okay' status on the brake output wire (Circuit 47), guiding the next diagnostic steps.

Wiring & Ground Locations

• K133 Trailer Brake Power Module (TBPM) — Located above the spare tire, mounted to a frame crossmember.. This module sends the test pulse and power down Circuit 47. Its wiring harness is a common failure point due to exposure, and the module itself is the subject of a GM service campaign for certain model years.
• Circuit 47 (Dark Blue Wire) — Runs from the Trailer Brake Power Module (K133) to pin 2 of the 7-pin trailer connector at the bumper.. This is the primary signal and power wire for the trailer brakes. Nearly all C1114 faults are related to an open, short to ground, or short to power on this specific circuit.
• Trailer Ground (White Wire) — Pin 1 of the 7-pin trailer connector. On the trailer side, this should be securely fastened to a clean, unpainted spot on the trailer frame.. A poor trailer ground is a specific cause listed in TSBs for a 'Service Trailer Brake System' message with code C1114.

"I Checked Everything" — The Actual Cause

• For 2020 and 2024 models, a scenario exists where all truck-side and trailer-side wiring may test perfectly fine. The actual cause can be voltage feedback from the trailer's own battery if it is charged to a higher state than the truck's battery. This creates a 'false' short-to-ground condition that the Trailer Brake Power Module (TBPM) detects, setting code C1114. The official fix is to replace the TBPM with an updated part (P/N 85073615) per GM Customer Satisfaction Program N232414840.

OEM Part Supersession History

• 22799842 → 23404450 — The updated 7-pin connector (23404450) features a stronger door spring to create a more secure and reliable connection with the trailer plug, reducing intermittent connection faults.
• Unknown → 85073615 — This updated Trailer Brake Power Module (TBPM) is designed to prevent false short-to-ground conditions caused by voltage feedback from a trailer's auxiliary battery.
  Heads up: This part is the specific fix for the condition described in GM program N232414840, primarily affecting 2020 and 2024 models.

Model Year Variations Within This Range

• 2019-2024 (approx.): The primary control module for the system can be either the Chassis Control Module (K38 CCM) or the Brake System Control Module (K160 BSCM), depending on the specific model year and vehicle configuration. Diagnostic paths in GDS2 may vary slightly.
• 2020, 2024: These specific model years are called out in GM Customer Satisfaction Program N232414840 for being susceptible to voltage feedback from a trailer battery, causing a false C1114 code. The fix is a specific updated Trailer Brake Power Module (P/N 85073615).