C1114 on 2024-2026 Chevrolet Silverado EV: Trailer Brake System Fault Guide

What's Unique About the 2024-2026 Chevrolet SILVERADO EV

The Chevrolet Silverado EV, built on the GM Ultium platform, features a sophisticated chassis control system designed to manage various trailer brake types. However, this sensitivity makes it prone to flagging faults when connected to certain trailers. Specifically, trailers with their own power sources (like batteries with solar chargers) or some Electric-Over-Hydraulic (EOH) brake systems can send voltage back to the truck, which the control module interprets as a fault, setting code C1114. GM has acknowledged these scenarios in multiple Technical Service Bulletins (TSBs), confirming the issue affects not just the Silverado EV but also the GMC Hummer EV and other GM trucks and SUVs.

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 power output to the trailer's electric brakes.
• Inability to adjust trailer brake gain using the in-cab controller.
• A recurring chime or alert while driving 🎬 Watch: What the service trailer brake warning looks like with a trailer connected.

Most Likely Causes

1. Towing a Trailer with an Onboard Power Source (Battery, Solar, Generator) 🔴 High Probability If the trailer's battery is at a higher state of charge than the vehicle's, it can feed voltage back into the truck's Trailer Brake Power Module, causing it to shut down and set C1114. This is a known issue for EVs when propulsion is first engaged, as the truck's main battery voltage can fluctuate.
   How to confirm: The issue occurs specifically when a trailer with its own charging system is connected. Disconnecting the trailer and clearing the code should make the code disappear. The issue may resolve itself once the truck's charging system brings its own battery to a higher state of charge.
   Typical fix: Per TSB #23-NA-149, the official fix is for a dealer to replace the Trailer Brake Control Module with an updated part designed to handle this voltage feedback scenario. The updated part is P/N 85073615, which supersedes P/N 23306694.
   Est. part cost: $20-$50 for the module itself, plus labor.
2. Incompatible Electric-Over-Hydraulic (EOH) Trailer Brakes 🟡 Medium Probability Certain EOH brake actuators, specifically the Hydrastar brand, are known to generate a voltage spike back into the truck's electrical system during light brake applications or even during the system's self-test. The Chassis Control Module detects this spike as a fault.
   How to confirm: The problem only occurs with a specific EOH-equipped trailer. Testing the truck with a standard electric-brake trailer or a trailer simulator tool (like GM's EL-52641) will show no faults. The issue is well-documented in TSB #PIT6212D.
   Typical fix: This is considered a trailer issue, not a truck issue. No repairs should be made to the vehicle. The trailer requires an adapter module, such as the Hydrastar HBA-CAM (P/N 381-7073), to be installed on the trailer to condition the signal and prevent the voltage spike.
   Est. part cost: $100-$150 (for trailer adapter)
3. Trailer Wiring or Connector Issues 🟡 Medium Probability The system is sensitive to poor connections, corrosion, or incorrect wiring. A poor ground on the trailer (white wire) or a short-to-power on the brake output circuit (dark blue wire, Circuit 47) are common culprits that trigger a 'Service Trailer Brake System' message. A short-to-ground on the same circuit will typically trigger a 'Check Trailer Wiring' message.
   How to confirm: Test the truck with a known-good trailer or a trailer simulator. If the code does not return, the fault is on the trailer side. Visually inspect the 7-pin connectors on both the truck and trailer for corrosion, bent pins, or moisture. A weak spring on the truck's connector door can also cause a loose connection.
   Typical fix: Repair the wiring on the trailer. Clean the connectors with a terminal brush and apply dielectric grease. Replacing the trailer-side plug with a high-quality OEM-style connector (e.g., Pollak) is often recommended by GM.
   Est. part cost: $20-$60

Diagnosis Steps

1. Read the specific message on the DIC. 'Service Trailer Brake System' often points to a short-to-power or bad ground, while 'Check Trailer Wiring' often points to a short-to-ground or open circuit on the brake output wire.
2. If a trailer is connected, disconnect it. Clear the DTC. If C1114 does not return, the fault is almost certainly with the trailer or the truck-trailer interface.
3. Identify the trailer's brake system. Is it standard electric, Electric-Over-Hydraulic (EOH), or does it have its own battery/charging system?
4. If the trailer has its own battery, consult TSB #23-NA-149. The fix is likely a dealer-installed updated Trailer Brake Control Module (P/N 85073615).
5. If the trailer has Hydrastar EOH brakes, consult TSB #PIT6212D. The issue is with the trailer generating a voltage spike. The fix is a trailer-side adapter module like the Hydrastar HBA-CAM.
6. If the trailer is a standard type, thoroughly inspect the 7-pin connectors on both the truck and trailer for corrosion, spread pins, or damage. Ensure the truck's connector door has a strong spring. Clean both sides and apply dielectric grease.
7. Inspect the trailer's wiring, paying close attention to the ground connection (white wire) at the trailer frame and the brake control wire (dark blue, Circuit 47).
8. If the code persists with no trailer connected, the issue is on the truck side. Inspect the truck's 7-pin connector and harness for damage, then have a professional diagnose the truck's internal wiring and Trailer Brake Power Module.

Parts You'll Likely Need

• Trailer Brake Control Module (OEM #85073615) — This is the updated part specified in TSB #23-NA-149 to fix issues with voltage feedback from trailers that have their own battery/charging systems. It supersedes the older part number 23306694.
  Trusted brands: ACDelco
  OEM price range: $20-$50
  Aftermarket price range: $20-$40
• 7-Pin Trailer Connector Socket (Truck-Side) (OEM #23404450) — Often replaced if the original is corroded or the spring-loaded door is weak, causing a poor connection. A secure connection is critical for the system to operate correctly. GM released this updated part with a stronger spring to combat this issue.
  Trusted brands: ACDelco, Pollak
  OEM price range: $40-$60
  Aftermarket price range: $20-$40
• Hydrastar Controller Adapter Module (for trailer) (OEM #HBA-CAM 381-7073) — This trailer-mounted part is the known solution for Hydrastar EOH brake systems that cause voltage spikes, preventing the C1114 code from setting. This is a trailer repair, not a truck repair.
  Trusted brands: Hydrastar
  OEM price range: $100-$150
  Aftermarket price range: $100-$150

Technical Service Bulletins (TSBs) & Recalls

• 23-NA-149: Addresses DTC C1114 when pulling a trailer with a battery, generator, or solar charger, recommending a new Trailer Brake Control Module (P/N 85073615).
• PIT6212D: Details the issue of Hydrastar EOH trailer brake systems causing a voltage spike, leading to C1114.
• PIT5509 Series (J, K, etc.): Explains how the Chassis Control Module determines trailer brake type and can be sensitive to wiring issues, leading to C1114. Differentiates the causes for 'Check Trailer Wiring' (short to ground) and 'Service Trailer Brake System' (short to power/bad ground).

Platform-Specific Known Issues

• Per TSB #23-NA-149, these vehicles are known to set C1114 when towing a trailer with its own power source (battery, generator, solar) due to voltage feedback. The fix is an updated Trailer Brake Control Module, P/N 85073615.
• Per TSB #PIT6212D, connecting to a trailer with a Hydrastar Electric-Over-Hydraulic (EOH) brake system can cause a voltage spike that the truck interprets as a fault, setting C1114. GM considers this a trailer issue, and the fix is a trailer-mounted adapter.
• A user on Reddit with a Silverado EV described towing a heavy trailer where the 'Check Trailer Wiring' message would appear after 10-15 minutes of driving, disabling the trailer brakes. After stopping, the error would sometimes clear, only to return again, indicating an intermittent connection or fault condition exacerbated by driving.

Hidden / Shadow Codes Worth Checking

• C1114 + 'Check Trailer Wiring' Message: Indicates the Chassis Control Module (CCM) or Brake System Control Module (BSCM) has detected a short to ground on the trailer brake output circuit (Circuit 47). (see via Visible on the Driver Information Center (DIC) in conjunction with scanning for the DTC. The GDS2 scan tool parameter 'Trailer Brake Control Output Circuit' will display 'Short to Ground'.)
• C1114 + 'Service Trailer Brake System' Message: Indicates the 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) in conjunction with scanning for the DTC. The GDS2 scan tool parameter 'Trailer Brake Control Output Circuit' will display 'Short to Power'.)

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', 'Electro-over hydraulic brakes', or if it's 'Undefined'. An incorrect or 'Undefined' reading with a trailer connected 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), which immediately guides the next diagnostic steps toward the specific type of electrical fault.

Wiring & Ground Locations

• Circuit 47 — Dark Blue wire running from the Trailer Brake Power Control Module (K133) to Pin 5 of the 7-pin trailer connector at the bumper.. This is the primary trailer brake control output circuit. The system continuously sends a test pulse on this wire to detect faults. Nearly all C1114 conditions relate to a short-to-ground, short-to-power, or open/high resistance on this specific circuit.
• Trailer Ground Circuit — White wire running to Pin 7 of the 7-pin trailer connector, which should be connected to a solid chassis ground on the trailer.. A poor trailer ground is a common cause for the 'Service Trailer Brake System' message with DTC C1114. The control module interprets the high resistance or voltage differential from a bad ground as a circuit fault.
• K133 Trailer Brake Power Control Module — On many modern GM trucks, this module is located above the spare tire, mounted to the frame rail.. This module is what sends power to the trailer brakes and is susceptible to damage from road debris and corrosion due to its location. It is also the module that gets replaced (with P/N 85073615) to solve the voltage feedback issue from trailers with batteries.

OEM Part Supersession History

• 23306694 → 85073615 — Updated design to handle voltage feedback from trailers equipped with their own battery/charging systems, preventing false C1114 codes.
  Heads up: The new part (85073615) should be used for all replacements, especially if the vehicle tows trailers with onboard power sources. Using old stock of 23306694 will not resolve the issue described in TSB 23-NA-149.
• 22799842 → 23404450 — The updated truck-side 7-pin connector incorporates a stronger door/cover spring to ensure a more secure connection with the trailer plug, reducing intermittent connection faults that can trigger C1114.