C1113 on 2015-2018 Chevrolet Tahoe: 'Service Trailer Brake' Causes and Fixes

What's Unique About the 2015-2018 Chevrolet TAHOE

The 2015-2018 Tahoe, along with other GM K2XX platform trucks and SUVs, is particularly sensitive to battery voltage. A weak or failing battery is a very common trigger for trailer brake system faults, including C1113. GM issued service bulletins specifically advising technicians to check the battery's state of health before performing any in-depth diagnostics for these codes. Additionally, the location of the Trailer Brake Power Module (TBCM), officially known as K133, on the frame rail above the spare tire makes its electrical connector susceptible to corrosion from road spray and debris.

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 not recognized when connected.
• Sluggish or slow engine cranking, indicating a weak battery.
• No power output to the trailer brakes when using the manual controller.
• ABS and traction control lights may also illuminate in some cases.

Most Likely Causes

1. Low Battery Voltage or Failing Battery 🔴 High Probability The trailer brake control system is sensitive to voltage drops and requires a stable voltage between 9.5 and 17 volts to operate correctly. GM TSB #PIT5521A and the combined TSB #PIT5529A specifically identify low battery voltage as a primary cause for C1113 and related codes, advising it be the first check.
   How to confirm: Test the battery's state of health and charge using a professional battery tester like a Midtronics GR8, as recommended by GM. A slow engine crank is also a strong indicator. Many auto parts stores will test your battery for free.
   Typical fix: Charge or replace the vehicle's battery. Ensure battery terminals and cables are clean and tight. A user on TahoeYukonForum confirmed a new battery resolved their issue after chasing other possibilities.
   Est. part cost: $150-$350
2. Corroded or Damaged Trailer Brake Power Module (TBCM) Connector 🔴 High Probability The TBCM is located on the driver's side frame rail, often above the spare tire, where its connector is exposed to water, salt, and dirt. TSB #PIT5529A notes this as a key cause, specifically calling out missing or dislodged cavity plugs in the connector that allow moisture intrusion.
   How to confirm: Visually inspect the TBCM connector for green or white corrosion, moisture, or pushed-out terminal pins. Disconnect the connector (with the key off) to check the pins and terminals on both sides. Ensure all rubber cavity plugs are present and fully seated.
   Typical fix: Clean the connector terminals with an electrical contact cleaner and a small brush. Apply dielectric grease upon reassembly to prevent future moisture. If corrosion is severe, the connector pigtail (e.g., GM #19329472) or individual terminals may need to be replaced.
   Est. part cost: $20-$60
3. Corroded or Damaged 7-Pin Trailer Connector 🟡 Medium Probability The 7-pin connector at the bumper is constantly exposed to the elements. Corrosion inside the socket or in the harness connector just behind it can cause shorts and communication issues.
   How to confirm: Inspect the terminals inside the truck's 7-pin socket and on the trailer's plug for corrosion. A user on TahoeYukonForum recommends taking the connector apart to clean it thoroughly. 🎬 See how to clean and inspect your trailer brake connectors. Also, unplug the large gray harness connector behind the 7-pin assembly and check for corrosion there.
   Typical fix: Clean the terminals thoroughly. If damaged, replace the 7-pin socket. GM issued an updated part (#23404450) with a stronger door spring to ensure a tighter connection. Many owners recommend using a quality aftermarket socket from Pollak, the OEM supplier.
   Est. part cost: $25-$75
4. Faulty Trailer Brake Power Module (TBCM) ⚪ Low Probability While less common than wiring or battery issues, the module itself can fail internally due to moisture intrusion or electronic failure.
   How to confirm: This is typically diagnosed by exclusion. If the battery, all wiring, and connectors are confirmed to be in good condition with proper power and ground, the module is the likely culprit. A bi-directional scan tool can help confirm a lack of communication with the module.
   Typical fix: Replace the Trailer Brake Power Module (OEM Part #85073617). The new module must be programmed to the vehicle's VIN by a dealer or a shop with SPS (Service Programming System) software to function correctly.
   Est. part cost: $80-$200

Rare But Worth Checking

• Poor Ground Connection: A loose or corroded ground for the TBCM can cause a variety of electrical issues, including this code. A Reddit user with a platform-mate GMC Sierra fixed their intermittent issue by cleaning and securing the ring terminal ground that bolts to the frame near the spare tire. Check the ground wire attachment point on the frame for integrity.
• Blown Fuse: A blown fuse in the under-hood fuse box can disable the trailer brake system. Check the large 30A J-case fuses for the trailer brake system (often labeled 'STUD 1' or 'STUD 2') and other related fuses. A short circuit on the trailer side can cause these fuses to blow.

Diagnosis Steps

1. Check the vehicle's battery first. Ensure it is fully charged and test its health with a professional-grade battery tester. Address any battery issues before proceeding. This is the first step recommended by GM.
2. If no trailer is connected, inspect the 7-pin trailer connector at the rear bumper for corrosion, moisture, or bent pins. Also, disconnect the large harness plug on the back of the 7-pin socket and inspect it for corrosion, as this is a common hidden failure point.
3. Check relevant fuses in the under-hood fuse box. Specifically look at the 30A J-case fuses for the trailer brake power studs.
4. Lower the spare tire to gain access to the Trailer Brake Power Module (TBCM) on the driver's side frame rail.
5. With the ignition off, disconnect the TBCM electrical connector. Carefully inspect both the module's pins and the connector's terminals for green/white corrosion, water intrusion, or pushed-out pins.
6. Check that all cavity plugs are present and fully seated in the connector to prevent future moisture entry, as specified in TSB #PIT5529A.
7. Locate and inspect the main ground wire for the TBCM, which should be bolted to the frame near the module. Ensure it is clean, tight, and free of corrosion.
8. If wiring and battery are good, test for proper power and ground at the TBCM connector using a multimeter.
9. If all external circuits test good, the TBCM itself is the likely point of failure and may require replacement and programming.

Parts You'll Likely Need

• Vehicle Battery — A weak or failing battery is a primary cause of this code on this platform, as confirmed by GM service bulletins.
  Trusted brands: ACDelco, Interstate, DieHard
  OEM price range: $200-$350
  Aftermarket price range: $150-$250
• Trailer Brake Power Module (OEM #85073617 (supersedes 23337305, 23114650, 23104453)) — This module can fail, but more often its connector is the problem. It is replaced only after all wiring and power issues are ruled out. Note that replacement requires programming. 🎬 Watch this walkthrough on replacing the trailer brake control module.
  Trusted brands: ACDelco (OEM), Dorman (601-237)
  OEM price range: $120-$200
  Aftermarket price range: $80-$150
• 7-Pin Trailer Connector Socket (OEM #84056018 (Socket), 23404450 (Updated Socket for 2014+ trucks with stronger door)) — The bumper-mounted connector is prone to corrosion and damage, which can cause this fault.
  Trusted brands: ACDelco (OEM), Pollak, Dorman
  OEM price range: $25-$75
  Aftermarket price range: $20-$50

Related Codes That Often Appear With This One

• C1112 — Relates to the trailer brake control relay low control circuit, often set for the same root causes like low voltage or corrosion.
• C1114 — Relates to the trailer brake control solenoids control circuit and is frequently seen with C1113 due to shared power and ground issues.
• C111B — Another code related to the trailer brake control system that is cited in the same TSBs as C1113, pointing to a common electrical fault.
• U1556 and U1505 — These are communication codes that can be set alongside C1113 when low voltage or corrosion disrupts the network communication with the Trailer Brake Power Module.

Technical Service Bulletins (TSBs) & Recalls

• PIT5529A: Addresses 'Service Trailer Brake' messages and codes C1112, C1113, C1114, C111B, U1556, U1505. It combines the advice of PIT5521A (check battery first) with a new focus on checking for corrosion in the TBCM connector due to missing cavity plugs.
• PIT5521A: A diagnostic tip for 'Service Trailer Brake' messages with codes C1112, C1113, C1114, and C111B, advising technicians to address any battery issues before performing any in-depth diagnostics.

Platform-Specific Known Issues

• TSB #PIT5521A explicitly states that a 'Service Trailer Brake Message' with DTC C1113 should first be diagnosed by checking the battery's state of health before any other complex diagnostics are performed.
• TSB #PIT5529A points to corrosion in the Trailer Brake Power Module (K133) connector, located near the spare tire, as a common cause for C1113 and related codes. It advises inspecting the connector and ensuring all cavity plugs are properly seated to prevent water intrusion, which can 'hydro-lock' and push the plugs out.

Mechanic-Grade Diagnostic Values

• TBCM Operating Voltage — expected: 9.5 - 17 Volts. Failure: The module will not run the DTC checks or operate correctly outside this range. Low voltage is a primary trigger for C1113.
• TBCM Relay Feedback Signal Voltage (GMT900-era, but principle is similar) — expected: 3.2 - 4.1 Volts. Failure: A voltage reading outside this range between the specified control circuit terminal and ground indicates a fault in the circuit or the TBCM itself.
• TBCM Power Supply at Connector — expected: 11 Volts or greater. Failure: Less than 11V at the IGN 1 voltage circuit (Pin 15) indicates a short to ground or an open/high resistance in the power feed to the module.

Hidden / Shadow Codes Worth Checking

• Trailer Brake Control Output Circuit Status: This is not a DTC, but a live data parameter that shows the specific electrical fault type detected by the control module on circuit 47. (see via Using a GM GDS2 scan tool, navigate to Chassis Control Module (CCM) -> Data Display. The parameter will read 'Okay', 'Short to Ground', 'Short to Power', or 'Unknown'.)

Scan Tool Commands That Help

• GDS2: CCM -> Data Display -> 'Trailer Brake Type' — Use this to verify if the Chassis Control Module is correctly identifying the connected trailer's brake system as 'Electro-magnetic' or 'Electro-over hydraulic'. An incorrect reading can point to wiring or trailer-side issues.
• GM SPS (Service Programming System): Trailer Brake Control Module Programming — This function is required after replacing the Trailer Brake Power Module (TBCM). The new module must be programmed with the vehicle's VIN to communicate with other modules and function correctly.

Wiring & Ground Locations

• K133 — The Trailer Brake Power Module itself, located on the driver's side frame rail, typically above the spare tire.. This is the module at the center of the C1113 fault. Its location makes its connector highly susceptible to corrosion, a primary cause of the code.
• TBCM Connector Pin 32 — Pin 32 (Red/White wire) on the K133 TBCM connector.. This is the main Battery Positive Voltage feed to the module. Verifying battery voltage at this pin is a critical step to rule out power supply issues.
• TBCM Ground (G3xx or G4xx) — A ring terminal bolted to the frame near the K133 module. Per GM's scheme, grounds in the rear of the vehicle are labeled G3xx (under rear seat area) or G4xx (rear of back seat to bumper).. A corroded or loose ground connection at this point will cause intermittent and difficult-to-diagnose electrical faults for the entire trailer brake system, including code C1113.

Real Owner Repair Stories

• YouTube video by user 'Fix It Frank' (2015 Chevrolet Silverado 2500 HD 6.0L) — Intermittent 'Service Trailer Brake System' warning that had been occurring for years and recently became almost constant.
  ❌ Tried (didn't work) The owner unplugged the in-dash switch to silence the warning prior to the final repair, implying it was not the cause.
  ✅ What actually fixed it Replacing the Trailer Brake Power Module (TBCM) located under the spare tire resolved the long-standing issue.
• YouTube video by user 'Biker Mike' (2015 GMC Sierra 2500 HD) — 'Service Trailer Brake System' message on the DIC.
  ❌ Tried (didn't work) Checked the wiring harness to the module and it appeared to be in good condition.
  ✅ What actually fixed it The owner used a BlueDriver scan tool which pointed to the module or wiring. After a visual wiring check, he replaced the Trailer Brake Power Module (GM Part shown in video), which fixed the problem.

OEM Part Supersession History

• 23104453, 23114650, 23337305 → 85073617 — Standard part evolution, likely for improved reliability or internal components.
  Heads up: The latest part number (85073617) is the correct service replacement for all previous versions on this platform. For 2015 models specifically, if the connector is damaged, the mating pigtail connector is GM P/N 19329472.

Model Year Variations Within This Range

• 2015-2018: The primary control module that communicates with the K133 Trailer Brake Power Module can vary. Depending on the model year and options, it may be the Chassis Control Module (CCM), an auxiliary CCM, or the Brake System Control Module (BSCM). This can affect which module a technician needs to query with a scan tool for diagnostics.