C1114 on 2011-2015 GMC Sierra 3500: Service Trailer Brake System Fixes

What's Unique About the 2011-2015 Gmc SIERRA 3500

The integrated trailer brake control (ITBC) system on these heavy-duty trucks is sophisticated, designed to identify and work with different types of trailer brakes (electromagnetic vs. electro-hydraulic). However, its sensitivity and the location of key components make it prone to issues. The Trailer Brake Power Module (TBCM or K133) and its connectors are located above the spare tire, exposing them to road salt and moisture, which leads to corrosion—a fact acknowledged by GM 🎬 Watch: A mechanic explains common failure points and corrosion issues. in TSB PIT5529A. Furthermore, TSB PIT5509J notes the system is very sensitive to trailer wiring quality, and many owner complaints for C1114 trace back to issues with the trailer's own wiring or a poor connection at the 7-pin plug, rather than a failure of the truck's components.

Diagnostic Flowchart

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

Generation note: This year range covers the end of the GMT900 platform (2011-2014) and the start of the GMTK2XX platform (2015). The C1114 fault is common on both generations. For 2014-2015 models, GM released an updated truck-side 7-pin connector (Part #23404450, which replaces #22799842) with a stronger door spring to combat poor connections, a frequent cause of this code as noted in TSB PIT5509J.

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 work intermittently.
• Audible chimes or alerts when a trailer is connected.
• DIC may display "Trailer Disconnected" intermittently if the connection is loose.

Most Likely Causes

1. Poor Connection at 7-Pin Trailer Connector 🔴 High Probability → Shop Trailer Wiring Harness The factory connector door spring can weaken, and many aftermarket trailer plugs do not meet SAE specifications, leading to intermittent connections from road vibration. TSB PIT5509J specifically recommends using a high-quality "Pollak HD" trailer-side plug and confirms GM released an updated truck-side connector (P/N 23404450) with a stronger spring for 2014+ models to fix this.
   How to confirm: With a trailer connected, wiggle the plug to see if the error message appears or disappears. Visually inspect the pins on both the truck and trailer for corrosion (white or green powder), spread pins, or damage.
   Typical fix: Clean both sides of the connector with a terminal brush and apply dielectric grease. If the truck's connector door is loose or terminals are worn, replace it with the updated GM part #23404450.
   Est. part cost: $25-$75
2. Trailer-Side Wiring Issues 🔴 High Probability GM TSB PIT5509J explicitly states that trailer wiring quality is often not up to automotive standards. Poor grounds (typically white wire), bad splices (using non-sealed butt connectors), and damaged wires on the trailer itself are extremely common triggers for the sensitive GM system.
   How to confirm: Test the truck with a known-good trailer or a dedicated trailer system tester as recommended by GM. If the code does not return, the fault is on the trailer. Inspect the trailer's wiring harness, especially the ground wire and the brake wire (dark blue), for damage or corroded connections at the frame and junction boxes.
   Typical fix: Repair damaged sections of wire using soldered, heat-shrunk connections. Ensure the trailer has a solid, clean ground connection to its frame.
   Est. part cost: $5-$50
3. Corroded Wiring or Connectors at Trailer Brake Power Module 🟡 Medium Probability → Shop Trailer Brake Control Module As cited in TSB #PIT5529A, the Trailer Brake Power Module (TBCM, K133) and its connectors are located above the spare tire, exposing them to road salt and moisture. Missing or dislodged cavity plugs in the connector can allow water intrusion, leading to terminal corrosion.
   How to confirm: Lower the spare tire to gain access. Disconnect the electrical connectors from the Trailer Brake Power Module and inspect for any signs of green or white corrosion, moisture, or pushed-out terminal pins.
   Typical fix: Clean the terminals carefully with a contact cleaner and a small brush. Apply dielectric grease upon reassembly. If corrosion is severe, the connector pigtail or the entire module may need to be replaced. Ensure all cavity plugs are present and fully seated.
   Est. part cost: $20-$250
4. Faulty Trailer Brake Power Module ⚪ Low Probability → Shop Trailer Brake Control Module While less common than wiring issues, the module itself (GM P/N 20850925) can fail internally due to moisture damage or electronic failure. This is often the final culprit after all external wiring has been verified as good.
   How to confirm: This is typically diagnosed by exclusion. If all wiring, connectors, grounds, and fuses have been thoroughly tested and found to be in good condition, the module itself is the likely culprit. A professional scan tool may be able to communicate directly with the module to confirm its status.
   Typical fix: Replace the Trailer Brake Power Module. This part is located above the spare tire and is typically held by a few bolts.
   Est. part cost: $100-$250
5. Weak or Failing Vehicle Battery ⚪ Low Probability → Shop Vehicle Battery TSB #PIT5529A explicitly states that low battery voltage can cause this and related trailer brake system codes. Before performing extensive diagnostics, the battery's state of health should be tested.
   How to confirm: Test the vehicle's battery using a professional-grade battery tester like the Midtronics GR8, as recommended by GM. A simple voltage check may not be sufficient to identify a weak battery under load.
   Typical fix: Replace the vehicle's battery if it fails the health test.
   Est. part cost: $150-$350

Rare But Worth Checking

• Faulty In-Dash Trailer Brake Controller Switch: The slider switch on the dashboard contains contacts that can wear out. While it can cause a 'Service Trailer Brake System' message, it is much less likely to be the cause of a C1114 code specifically, which usually points to the output circuit. Owners have reported replacing this part with no success for C1114.
• Incompatible Aftermarket Trailer Accessories: Some aftermarket devices, like certain electronic sway controllers or electric-over-hydraulic brake adapters that are not designed for GM's system, can interfere with the diagnostic pulses and trigger a C1114 code, as noted in TSB PIT5509J.

Diagnosis Steps

1. Check vehicle battery health first, as recommended by TSB PIT5529A.
2. Read the code with an OBD-II scanner and note the exact message on the DIC. Per TSB PIT5509J, 'Service Trailer Brake' often means a short to power or bad ground, while 'Check Trailer Wiring' suggests a short to ground.
3. If a trailer is connected, disconnect it and clear the codes. If the code does not return, the problem is almost certainly on the trailer side. Test with a known-good trailer or a trailer brake circuit tester to confirm.
4. Thoroughly inspect the truck's 7-pin connector for corrosion, moisture, or spread/damaged pins. Ensure the connector door provides firm pressure. If loose, consider replacing with the updated P/N 23404450.
5. Inspect the trailer's 7-pin plug and wiring for damage, especially the ground (white) and brake control (dark blue) wires.
6. Check the 30A fuse (often labeled STUD 2) for the Trailer Brake Control system in the under-hood fuse block.
7. Lower the spare tire and locate the Trailer Brake Power Module (TBCM). Disconnect and inspect its electrical connectors for corrosion or damage as noted in TSB #PIT5529A.
8. Trace the wiring harness (specifically the dark blue Circuit 47) from the 7-pin connector to the module, looking for any chafing, breaks, or signs of corrosion, paying attention to the X411 inline connector on the frame rail.
9. If all wiring and connections are confirmed to be good, the Trailer Brake Power Module (P/N 20850925) is the most likely culprit. Note that this part may require dealer programming.

Parts You'll Likely Need

• Trailer Connector Socket (OEM #23404450) — GM released this updated part with a stronger door spring to ensure a secure connection, a very common failure point. Replaces original part 22799842.
• Trailer Brake Power Module (OEM #20850925) — This module, located above the spare tire, can fail due to moisture intrusion or internal electronics. It is often the final fix when all wiring checks out.
• Dielectric Grease — Essential for protecting all cleaned electrical connections (7-pin, module connector) from future corrosion.
• Trailer-Side 7-Pin Plug (OEM #Pollak 12-706 (recommended by GM TSB)) — Many trailer-side issues are caused by low-quality plugs. TSBs recommend using a heavy-duty Pollak brand plug for a reliable connection.

Related Codes That Often Appear With This One

• C1112 — This code relates to the trailer brake control relay circuit and is often triggered by the same wiring harness or module issues that cause C1114. TSB #PIT5529A and #PIT4595J explicitly link these codes.
• C1113 — Indicates a short to battery in the relay control circuit, which can be caused by corrosion or damage in the same harness. TSB #PIT5529A lists this as a related code.
• U1556 / U1505 — These are communication codes that can appear when corrosion at the Trailer Brake Power Module connector affects multiple circuits, disrupting communication between modules. TSB #PIT5529A also lists these codes.

Technical Service Bulletins (TSBs) & Recalls

• PIT5509J: Provides detailed diagnostic tips, explaining how different DIC messages ('Check Trailer Wiring' vs. 'Service Trailer Brake System') point to different fault types (short to ground vs. short to power/bad ground). Recommends using a Pollak brand trailer-side plug.
• PIT5529A: Links C1114 with other codes (C1112, C1113, U1556, U1505) and points to two primary causes: low vehicle battery voltage or corrosion in the Trailer Brake Power Module connector due to missing cavity plugs.
• PIT4595J: Specifically addresses diagnostic strategies for the 'Service Trailer Brake' message accompanied by codes C1114 and C1112.

Platform-Specific Known Issues

• TSB #PIT5509J notes that this code can set when the Chassis Control Module has trouble determining the type of trailer brake system being used, often due to an open or high resistance in the brake output circuit (Circuit 47).
• TSB #PIT5529A specifically calls out inspecting the battery and Trailer Brake Power Module connector for corroded terminals as a primary diagnostic step for code C1114.
• TSB #PIT4595J provides diagnostic tips for dealership technicians when encountering a 'service trailer brake' message with codes C1114 and C1112, highlighting it as a known issue.

Mechanic-Grade Diagnostic Values

• Voltage between Trailer Brake Control Relay control circuit terminal A and ground (Ignition ON) — expected: 3.2-4.1 V. Failure: A reading less than 3.2V suggests a short to ground or open/high resistance. A reading greater than 4.1V suggests a short to voltage.
• Resistance between Trailer Brake Control Relay ground circuit terminal B and ground (Ignition OFF) — expected: Less than 5 ohms. Failure: A reading greater than 5 ohms indicates an open or high resistance in the ground circuit.
• Voltage at the brake controller's output wire (typically blue) when manually activated — expected: Should read ~12V. Failure: A reading significantly lower than 12V or 0V indicates a problem with the controller or its wiring.

Scan Tool Commands That Help

• GDS2 (GM Techline): Data Display > Trailer Brake Type — To verify if the Chassis Control Module (CCM/BSCM) is correctly identifying the connected trailer's brake system as 'Electro-magnetic', 'Electro-over hydraulic brakes', or 'Undefined'. An incorrect reading can point to a trailer-side issue or incompatibility.
• GDS2 (GM Techline): Data Display > Trailer Brake Control Output Circuit — This live data parameter directly shows the fault status of Circuit 47 as detected by the module. It will display 'Okay', 'Short to Ground', 'Short to Power', or 'Unknown', which is more specific than the DTC alone and helps guide electrical testing.

Wiring & Ground Locations

• K133 Trailer Brake Power Control Module — Located on a bracket above the spare tire, mounted to a frame cross-member.. This is the main control unit for the trailer brake output. Its location makes it highly susceptible to moisture and corrosion from road spray, a primary cause of C1114. The connectors are a critical inspection point.
• Circuit 47 (Dark Blue Wire) — Runs from the Trailer Brake Power Control Module (K133) to Pin 2 of the 7-way bumper connector. It passes through the X411 inline connector on the frame rail.. This is the specific circuit monitored for faults that trigger C1114. Any short to ground, short to power, or open/high resistance along this wire will cause the code.
• X411 Connector — An inline harness connector located on the driver's side frame rail, between the TBCM and the rear bumper 7-way connector.. This is a common point for corrosion and wiring damage. A video from 'Shaners Mechanic Life' shows this connector near the spare tire and recommends inspecting it for damage or corrosion after checking the bumper plug and TBCM.
• STUD 2 Fuse — A 30A J-Case fuse in the under-hood fuse block, typically labeled for trailer brake power.. This fuse supplies the main power to the trailer brake system. While a blown fuse might indicate a dead short, it should be checked early in the diagnostic process.

Real Owner Repair Stories

• YouTube channel 'the Fab Forums' (2014 Chevrolet Silverado (platform equivalent)) — Persistent "Check Trailer Wiring" message on the DIC.
  ❌ Tried (didn't work) Initial scan with Snap-on Verus would not communicate with the trailer brake module., Used an Autel scanner which successfully read the C1114 code., Unplugging the 7-pin connector and clearing codes did not resolve the issue, suggesting the fault was on the truck side.
  ✅ What actually fixed it The final fix involved replacing both the Trailer Brake Power Module (P/N 20850925) and the rear 7-pin bumper connector, which had a missing/damaged pin. After replacement, all codes were cleared successfully. The video also notes that identifying the vehicle as a 2015 model in the scan tool was necessary to access the correct module for diagnostics on this specific 2014 truck.

OEM Part Supersession History

• 20850925 → 85073615 — GM regularly updates part designs to integrate new materials and technologies. This is the newer replacement part number for the Trailer Brake Power Module.
  Heads up: The replacement module (85073615) may require programming by a dealer or a shop with GM-certified tools upon installation.
• 22799842 → 23404450 — The updated truck-side 7-pin connector incorporates a stronger door spring to ensure a more secure connection with the trailer plug, reducing intermittent faults.

Model Year Variations Within This Range

• 2014-2015 (GMTK2XX Introduction): For 2014-2015 models, GM introduced an updated truck-side 7-pin connector (P/N 23404450) with a stronger spring to combat poor connections, a frequent cause of C1114. TSB PIT5509J specifically calls out this part for 2014-2018 models.
• 2011-2014 (GMT900): On these models, when the system detects EOH brakes, it will not provide any output when the brake pedal is applied at 0 mph. This is normal operation and not a fault. This behavior differs from later models.