C1113 on 2015-2018 Chevrolet Silverado 2500: Service Trailer Brake System Fixes

What's Unique About the 2015-2018 Chevrolet SILVERADO 2500

On this generation of Silverado HD trucks, the trailer brake control module is mounted on a frame crossmember, directly above the spare tire. This location makes its electrical connector highly susceptible to water, road salt, and dirt kicked up by the rear wheels. As a result, corrosion on the connector pins is a very common and well-documented cause for code C1113. GM TSB PIT5529A specifically notes that water can enter the connector from a missing or dislodged cavity plug, and that 'connector hydro-locking' can push the plugs out during connection, exacerbating the problem.

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.
• Integrated trailer brake controller is disabled and shows no output.
• Trailer brakes do not apply when using the manual slider or when pressing the brake pedal.
• Trailer connection is not recognized by the truck.
• Slow engine crank (may accompany the message, indicating a weak battery).

Most Likely Causes

1. Weak or Failing Vehicle Battery 🔴 High Probability → Shop Vehicle Battery Modern trucks have high electrical demands. A battery with low voltage, especially during engine cranking, can cause modules like the TBCM to set fault codes. TSB PIT5521A was issued specifically to address this.
   How to confirm: Test the battery's state of health and charge using a professional-grade battery tester like a Midtronics GR8, as recommended by GM in TSB PIT5529A. A simple voltage check is often not sufficient. A slow cranking engine is a strong clue.
   Typical fix: Recharge or replace the vehicle's battery. This should always be the first step before further diagnosis.
   Est. part cost: $150-$350
2. Corroded Trailer Brake Power Module (TBPM) Connector 🔴 High Probability → Shop Trailer Brake Control Module The module is located above the spare tire, exposing its connector to moisture and road debris. TSB PIT5529A identifies this as a primary cause, often due to missing or dislodged cavity plugs allowing water intrusion.
   How to confirm: Lower the spare tire, locate the TBPM on the frame crossmember, disconnect its electrical connector, and visually inspect the pins and terminals on both the harness and module side for green or white corrosion or water intrusion. Specifically check that all small rubber cavity plugs are present and fully seated in the aconnector body.
   Typical fix: Clean the connector terminals with electrical contact cleaner and a small brush. If corrosion is severe, the connector pigtail and sometimes the module must be replaced. Apply dielectric grease before reassembly and ensure the connector seals and cavity plugs are intact.
   Est. part cost: $25-$75 for a connector pigtail.
3. Blown Fuse 🟡 Medium Probability
   How to confirm: Check the under-hood fuse box for blown fuses related to the trailer brake system. Specifically check fuses labeled for the trailer brake controller (ITBC) or trailer battery power.
   Typical fix: Replace the blown fuse with one of the identical amperage rating. If the new fuse blows immediately, it indicates a short circuit that requires further diagnosis.
   Est. part cost: $1-$5
4. Damaged Wiring Harness ⚪ Low Probability The harness running to the rear of the truck can be susceptible to physical damage, chafing against the frame, or corrosion further away from the main connector.
   How to confirm: Visually inspect the wiring leading to the Trailer Brake Power Module and the 7-pin trailer connector for any breaks, chafing, or signs of repair. Perform continuity and short-to-ground/voltage tests on the relevant circuits with a multimeter, as outlined in the service manual.
   Typical fix: Repair the damaged section of the wiring harness. This can be complex and may require a professional.
   Est. part cost: $10-$50 for wiring repair supplies.

Rare But Worth Checking

• Faulty Trailer Brake Power Module (TBPM): → Shop Trailer Brake Control Module This module is often replaced unnecessarily. It should only be considered faulty after all other possibilities (battery, wiring, 🎬 See this walkthrough on replacing the module above the spare tire. connectors, fuses) have been definitively ruled out through testing.
• Poor Connection at 7-Pin Bumper Connector: Corrosion inside the truck's 7-pin bumper connector or the use of a worn or out-of-spec trailer plug can cause intermittent connection issues and trigger faults. This is an easy first place to clean and inspect.
• Faulty In-Dash Trailer Brake Control Switch: → Shop Trailer Brake Control Module The switch assembly in the dashboard containing the manual slider and gain buttons 🎬 Watch: A quick guide to fixing the service trailer brake message. can fail internally, causing a 'Service Trailer Brake System' message. This is a known, though less common, failure point.

Diagnosis Steps

1. Address Battery Health First: Fully charge and test the vehicle's battery with a professional tester (like the GM-recommended Midtronics GR8). A weak battery is a known cause for this code. Resolve any battery issues before proceeding.
2. Check for Other Codes: Scan all vehicle modules for other DTCs. Pay close attention to codes C1112, C1114, C111B, and any 'U' (communication) codes, as they provide valuable diagnostic clues.
3. Inspect Fuses: Open the under-hood fuse block and inspect all fuses related to the trailer brake system. Replace any that are blown.
4. Inspect the TBPM Connector: Lower the spare tire to gain access to the Trailer Brake Power Module (TBPM). Disconnect the main electrical harness and thoroughly inspect both the harness connector and the module pins for any signs of water intrusion, or green/white corrosion. Pay close attention to missing or dislodged rubber cavity plugs in the connector body, a known issue from TSB PIT5529A.
5. Inspect the 7-Pin Bumper Connector: Check the truck's 7-pin trailer connector at the bumper for corrosion, debris, or bent pins.
6. Test Circuits: If no obvious issues are found, use a multimeter to test the 'solid state relay enable circuit' mentioned in the code definition for a short to voltage, as well as checking for proper power and ground at the TBPM connector per the service manual.
7. Consider the Module: If all wiring, connectors, and the battery test normal, the Trailer Brake Power Module itself may have failed.

Parts You'll Likely Need

• Vehicle Battery — A weak or failing battery is a primary cause of this code as specified by GM TSB PIT5521A and PIT5529A.
  Trusted brands: ACDelco, Interstate, DieHard
  OEM price range: $200-$350
  Aftermarket price range: $150-$250
• Trailer Brake Power Module Connector Pigtail (OEM #ACDelco PT2712 (GM #13584094)) — The original connector is prone to corrosion due to its location. Replacing the connector pigtail is the standard repair for corroded terminals. This specific part number is the widely recognized replacement.
  Trusted brands: ACDelco (OEM), Dorman
  OEM price range: $40-$75
  Aftermarket price range: $25-$50
• Trailer Brake Power Module (OEM #85073617, 84108373 (verify by VIN)) — This part is replaced only if it is confirmed to be faulty after all wiring, power, and ground checks have been completed. Part numbers can vary.
  Trusted brands: ACDelco (GM Genuine)
  OEM price range: $150-$250
  Aftermarket price range: $100-$180

Related Codes That Often Appear With This One

• C1112 — Relates to the Trailer Brake Control Relay Low Control Circuit, often set along with C1113 due to the same root causes like corrosion or low voltage.
• C1114 — Relates to the Trailer Brake Control Solenoids Control Circuit and shares the same power and ground circuits, making it susceptible to the same faults.
• C111B — Another trailer brake system code often triggered by low battery voltage, as noted in TSB PIT5521A and PIT5529A.
• U1505 / U1556 — These are communication codes that can be set when corrosion or wiring issues on the trailer brake module connector disrupt network communication, as noted in TSB PIT5529A.

Technical Service Bulletins (TSBs) & Recalls

• PIT5521A: Advises checking for and addressing battery issues first when C1113 and other trailer brake codes are present.
• PIT5529 / PIT5529A: Points to a corroded Trailer Brake Power Module connector as a likely cause for C1113 and recommends inspection and replacement of the connector if corroded.

Platform-Specific Known Issues

• A known issue documented in TSB #PIT5529A involves water and dirt entering the Trailer Brake Power Module connector, causing corrosion and triggering codes C1112, C1113, C1114, and others. The TSB specifically calls out that missing or improperly seated cavity plugs in the connector body are a primary cause of the water intrusion.

Mechanic-Grade Diagnostic Values

• Solid State Relay Enable Circuit Voltage — expected: DTC C1113 sets if the TBCM detects a short to voltage on this circuit.. Failure: A voltage reading significantly higher than expected, approaching battery voltage, indicates a short.
• Ground Circuit Resistance at TBPM Connector — expected: Less than 5.0 ohms between the ground circuit terminal and a good chassis ground.. Failure: A reading higher than 5.0 ohms indicates high resistance in the ground circuit, which can cause various faults.
• Battery Positive Voltage at TBPM Connector — expected: A test lamp should illuminate when connected between the B+ circuit terminal and ground.. Failure: If the test lamp does not light, it indicates a loss of battery power to the module, likely from a blown fuse or broken wire.

Scan Tool Commands That Help

• GDS2: Chassis Control Module (CCM) -> Data Display -> 'Trailer Brake Control Output Circuit' — This parameter helps differentiate the type of fault. For C1113, it may read 'Short to Power', confirming the diagnostic trouble code's definition and pointing the technician toward a wiring issue rather than a component failure.
• GDS2: Chassis Control Module (CCM) -> Data Display -> 'Trailer Brake Type' — When diagnosing trailer connection issues that accompany C1113, this parameter shows if the module correctly identifies the trailer as 'Electro-magnetic' or 'Electro-over hydraulic brakes'. An 'Undefined' reading with a trailer connected points to a communication or connection problem.

Wiring & Ground Locations

• Trailer Brake Power Module (TBPM) Connector (X411) — On the frame crossmember, directly above the spare tire.. This is the primary point of failure due to corrosion from water and road debris. All power, ground, and control signals for the trailer brakes pass through this connector.
• Pin 33 (Solid State Relay Enable) — At the TBPM connector (X411). The wire is typically Yellow/Black.. DTC C1113 specifically flags a short to voltage on this circuit. Testing for voltage at this pin is a direct confirmation of the fault condition.
• Pin 32 (Battery Positive Voltage) — At the TBPM connector (X411). The wire is typically Red/White.. This is the main power feed for the module. Verifying battery voltage here is a critical first step in electrical diagnosis.
• Ground G401 — On the left rear of the frame.. This is a common ground point for several rear vehicle components, including the trailer wiring harness. A poor connection at G401 can cause intermittent and difficult-to-diagnose trailer brake faults.

Real Owner Repair Stories

• YouTube channel '2017 GM Truck 1500 4x4 Service Trailer Brake System Message. The Fix Part 2' (2017 Chevrolet Silverado) — Service Trailer Brake System message, loss of communication with the 'chassis control module auxiliary' (the TBPM).
  ❌ Tried (didn't work) Initial fuse checks did not reveal the problem.
  ✅ What actually fixed it The technician found a corroded power feed wire (red wire, circuit 2040) within the main wiring harness near the driver-side running board motor. The corrosion was hidden inside the cloth tape of the harness and was not visible at the module connector itself. Repairing this section of wire restored power and communication to the module, clearing the code.

OEM Part Supersession History

• 23104453, 23114650, 23337305 → 85073617 — Standard part evolution, likely for improved reliability or manufacturing efficiency.
  Heads up: The newer part number 85073617 is the correct service replacement for the earlier numbers on these vehicles.
• 23145874 → 84108373 — This supersession is for the in-dash trailer brake control switch assembly, not the module under the truck.
  Heads up: Part 84108373 is the correct replacement for the dash switch. It's important not to confuse this with the Trailer Brake Power Module (TBPM) which is a separate component.

Model Year Variations Within This Range

• 2017-2018: For the 2017 model year, the Silverado HD models received the new 6.6L Duramax L5P turbo-diesel V8 engine. This update included a new hood with a prominent air intake vent. While the core trailer brake system functionality remained the same, wiring harnesses and module software calibrations may have minor differences compared to the 2015-2016 LML engine models.