C1112 on 2015-2018 Chevrolet Silverado 1500: Trailer Brake System Fault Causes & Fixes

What's Unique About the 2015-2018 Chevrolet SILVERADO 1500

On this generation of Silverado (K2XX platform), the various control modules are highly sensitive to vehicle voltage. As confirmed by multiple GM Technical Service Bulletins (PIT5521A, PIT5529A), a battery that is even slightly weak can cause the trailer brake system to set a C1112 fault during its startup self-test, even if the battery has enough power to start the engine. This makes a professional battery load test the mandatory first step in diagnosis, often saving owners from unnecessarily replacing expensive control modules. Many owners in forums report that a new battery resolved the issue, even when the old battery seemed fine.

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 activate when applied manually or with the truck's brakes
• The trailer gain and output display on the DIC may be blank or show an error
• The system may not recognize when a trailer is connected
• Audible chime or alert repeating while driving

Most Likely Causes

1. Weak or Failing Vehicle Battery 🔴 High Probability → Shop Vehicle Battery As documented in TSBs PIT5521A and PIT5529A, the control modules on this truck are extremely sensitive to voltage drops during startup. A weak battery can cause intermittent faults in the trailer brake system before causing a no-start condition. This is the most common cause reported by owners. 🎬 Watch: Common failure points and fixes for the trailer brake warning.
   How to confirm: Test the battery's state of health and charge using a professional-grade load tester (like a Midtronics GR8), not just a multimeter. A simple voltage reading is not sufficient to identify a battery that is weak under load.
   Typical fix: Recharge or replace the vehicle's battery. Ensure all battery terminals and ground connections are clean and tight. Many owners on forums like Reddit have confirmed that replacing an aging battery was the definitive fix.
   Est. part cost: $150-$350
2. Corroded Trailer Brake Power Module (TBPM) Connector 🔴 High Probability → Shop Trailer Brake Control Module The module is located on the driver's side frame rail, above the spare tire, an area highly exposed to road spray and debris. TSB PIT5529A notes that water intrusion from missing or dislodged cavity plugs in the connector is a frequent cause of corrosion and this code. The connector can become 'hydro-locked', forcing the plugs out when connected.
   How to confirm: Lower the spare tire for access. Unplug the module's electrical connector (often labeled X411) and inspect thoroughly for green or white corrosion ('blue crusties'), moisture, or bent/damaged pins. Check that all small rubber cavity plugs are present and seated.
   Typical fix: Clean the connector terminals with a specialized contact cleaner and a small brush. If corrosion is severe, the connector pigtail may need to be cut out and replaced. Apply dielectric grease before reconnecting to prevent future moisture intrusion.
   Est. part cost: $20-$80
3. Blown Fuse 🟡 Medium Probability A short circuit in the trailer's own wiring is a common reason for blowing the truck's trailer-related fuses. The under-hood fuse block is the primary location for these fuses.
   How to confirm: Check the fuses related to the trailer brake system in the under-hood fuse box. Specifically, 🎬 See this guide to locate and replace trailer brake fuses. check the 30A J-case fuse at position F1 (for 2017-2018 models) or other trailer-related fuses like F14, F15, F17, and F34.
   Typical fix: Replace the blown fuse. If it blows again immediately or when a trailer is connected, a short circuit exists that must be diagnosed, likely in the trailer wiring or the harness leading to the 7-pin connector.
   Est. part cost: $5-$15
4. Faulty Trailer Brake Power Module (TBPM) ⚪ Low Probability → Shop Trailer Brake Control Module While the module itself can fail internally, it is far more common for the issue to be with its power supply (battery) or connectors. Many modules are replaced unnecessarily. Internal failure is often due to moisture getting past the seals or connector pins.
   How to confirm: This is typically diagnosed by exclusion. If the battery is healthy, all fuses are good, and all wiring/connectors are clean and show proper voltage/ground, the module itself is the likely culprit. A scan tool can be used to check for communication with the module.
   Typical fix: Replace the Trailer Brake Power Module (GM part #85073617). The new module may require programming by a dealer or a properly equipped independent shop to function correctly with the vehicle's VIN.
   Est. part cost: $80-$150

Rare But Worth Checking

• Poor Ground Connection (G401): TSB PIT4595J recommends checking the G401 ground for proper connection. This ground point is located on the driver's side frame rail, near the rear of the truck, and can become corroded, causing various electrical issues. It is a common source of high resistance faults.
• Damaged Wiring Harness: The wiring harness running to the rear of the truck is exposed. Damage from road debris, improper jacking, or previous repairs can cause a short or open circuit, leading to code C1112. Pay special attention to the dark blue wire (Circuit 47), as damage to it is a direct cause of this code.
• Corrosion in 7-pin Bumper Connector: Moisture and road salt can cause corrosion inside the 7-pin trailer connector on the bumper, or in the large harness plug that connects to the back of it. This can cause shorts or high resistance that the system detects as a fault.

Diagnosis Steps

1. Read all Diagnostic Trouble Codes (DTCs) from all modules using a capable OBD-II scanner.
2. CRITICAL: Perform a professional battery health and load test using a tool like a Midtronics GR8. Address any battery issues before proceeding. This is the first step mandated by GM TSBs.
3. Inspect all fuses in the under-hood fuse block related to the trailer towing system. Specifically check F1, F14, F15, F17, and F34. Replace any that are blown.
4. Lower the spare tire to gain access to the driver's side frame rail.
5. Locate the Trailer Brake Power Module (TBPM), also known as K133. Disconnect its electrical connector and inspect both sides for any signs of corrosion, moisture, or damaged pins. Ensure all cavity plugs are present and fully seated.
6. If corrosion is found, clean the terminals thoroughly with electrical contact cleaner. If damage is severe, replace the connector pigtail. Apply dielectric grease upon reassembly.
7. Locate and inspect ground G401 on the driver's side frame rail. Disassemble, clean the connection point to bare metal, and re-secure it tightly.
8. Inspect the wiring harness leading to the TBPM and the 7-pin bumper connector for any visible damage, chafing, or poor repairs. Pay close attention to the dark blue wire (Circuit 47).
9. Inspect the 7-pin trailer connector at the rear bumper for corrosion or damage, including the harness plug on the back side of the socket.
10. If all wiring, connectors, and the battery check out, the Trailer Brake Power Module itself is the most likely remaining cause. Replacement 🎬 Watch: Step-by-step walkthrough for replacing the trailer brake power module. may require programming.

Parts You'll Likely Need

• Vehicle Battery — A weak battery is the most common cause of this code on this platform, as specified in multiple GM service bulletins.
  Trusted brands: ACDelco, Interstate, DieHard
  OEM price range: $200-$350
  Aftermarket price range: $150-$250
• Trailer Brake Power Module (OEM #85073617) — This module can fail, but more often its connector corrodes. The part number 85073617 supersedes several previous versions, including 23104453, 23114650, and 23337305.
  Trusted brands: ACDelco (GM Genuine), Dorman (601-237), Standard Motor Products (TBM003)
  OEM price range: $80-$150
  Aftermarket price range: $40-$70
• Trailer Brake Power Module Connector Pigtail (OEM #ACDelco PT2713) — If the connector is too corroded to be cleaned, it must be cut out and a new pigtail spliced in.

Related Codes That Often Appear With This One

• C1114 — This code is also related to the trailer brake control system and is frequently set alongside C1112, as noted in TSBs PIT5529A and PIT4595J.
• C111B — Another trailer brake system code often triggered by the same root causes, particularly low battery voltage, as mentioned in TSB PIT5521A.
• U1556 / U1505 — These are communication codes that can be set along with C1112 when low voltage or connection issues disrupt the network, as seen in TSB PIT5529A.

Technical Service Bulletins (TSBs) & Recalls

• PIT5529A: Service Trailer Brake Message With DTCs C1112, C1113, C1114, C111B, U1556, and/or U1505. Points to low battery voltage or corroded TBPM connector.
• PIT5521A: Diagnostic Tip for Service Trailer Brake Message with DTCs C111B, C1112, C1113, C1114. Advises addressing battery issues first.
• PIT4595J: Diagnostic tips for a service trailer brake message with DTC C1114 and C1112. Recommends checking ground G401.

Platform-Specific Known Issues

• TSB PIT5529A directly addresses the "Service Trailer Brake" message with code C1112, identifying the two primary causes as low battery voltage or water intrusion into the Trailer Brake Power Module connector from a missing cavity plug.
• TSB PIT5521A specifically advises technicians to address any battery health issues *before* performing any in-depth diagnostics for C1112, highlighting how common this root cause is.
• The location of the Trailer Brake Power Module above the spare tire makes it extremely vulnerable to corrosion, a point repeatedly made in owner forums and repair videos.

Mechanic-Grade Diagnostic Values

• TBCM Relay Feedback Signal voltage (Scan Tool Data) — expected: 3.2 - 4.1 Volts. Failure: A reading higher than 4.1V suggests a short to voltage; a reading lower than 3.2V suggests a short to ground or an open circuit.
• Voltage at Trailer Brake Power Control Module (K133) 10-volt relay control circuit (Terminal E) — expected: 9 - 11 Volts. Failure: A reading less than 9V suggests a short to ground or open/high resistance. A reading greater than 11V suggests a short to voltage.
• Ground circuit resistance at trailer brake control relay connector (Terminal B to ground) — expected: Less than 5 ohms. Failure: Resistance greater than 5 ohms indicates an open or high resistance in the ground circuit.

Hidden / Shadow Codes Worth Checking

• C1112 00: The '00' is a symptom byte that specifies the fault as 'Trailer Brake Control Relay Low Control Circuit'. It provides more detail than the base code alone. (see via Professional GM scan tools like the Tech 2 or GDS2 will display the code with its corresponding symptom byte.)

Scan Tool Commands That Help

• GDS2 / Tech 2: Monitor 'TBCM Relay Feedback Signal' Data PID — This is a primary diagnostic step to check the health of the trailer brake control circuit (dark blue wire 47). It helps quickly determine if a short to voltage (>4.1V) or short to ground/open (<3.2V) exists without extensive manual probing.
• GDS2: Monitor 'Trailer Brake Control Output Circuit' Status — This data parameter directly tells you the module's interpretation of the circuit's state, displaying 'Okay', 'Short to Ground', or 'Short to Power'. This is useful for confirming a fault on circuit 47, especially when a trailer is connected.
• GDS2 / Tech 2: Command Trailer Brake Relay ON/OFF — This is a bidirectional test to check the functionality of the trailer brake relay and the integrity of its control circuit. It can be used with a test lamp at the 7-pin connector to visually confirm if the command is working.

Wiring & Ground Locations

• K133 — On the driver's side frame rail, typically located above the spare tire.. This is the Trailer Brake Power Module itself. Its connector is highly susceptible to corrosion from road spray, which is a primary cause of code C1112 as noted in TSB PIT5529A.
• G401 — On the driver's side rear frame rail, often near or on the spare tire hoist bracket, behind the rear tire.. This is a critical ground point for the rear lighting and trailer brake system. TSB PIT4595J specifically calls for inspecting this ground for looseness or corrosion as a key diagnostic step for C1112.
• Circuit 47 (Dark Blue Wire) — Runs from the trailer brake control relay, along the frame harness, to the K133 Trailer Brake Power Module, and finally to Pin 3 of the 7-way bumper connector.. This is the main trailer brake control output wire. The control module continuously sends a test pulse on this circuit to detect faults. A short or open on this specific wire is a direct cause of codes C1112 and C1114.
• X411 — This is the designation for the main electrical connector at the K133 Trailer Brake Power Module.. This connector is the most common point of failure due to corrosion. Inspecting its pins and ensuring all cavity plugs are seated is a mandatory step per TSB PIT5529A.

Real Owner Repair Stories

• YouTube channel '5-9 Motorsports' (2014-2018 GM Truck (specific year not mentioned, but within range)) — "Service Trailer Brake System" message on the DIC.
  ❌ Tried (didn't work) Replacing the in-dash trailer brake controller switch module.
  ✅ What actually fixed it The #2 30-amp fuse in the under-hood fuse box, for the 'Trailer Battery', was blown. Replacing the fuse cleared the message and fixed the problem.
• YouTube channel 'Phillip Bailey' (2008 GM 2500HD (older model, but identical fault logic)) — "Service Trailer Brake System" message with codes C1112, C1114, C1119.
  ❌ Tried (didn't work) Replacing the trailer brake control relay., Load testing the wiring from the relay to the module., Replacing the trailer brake control module.
  ✅ What actually fixed it Found two wires were crossed in the trailer brake relay plug from a previous incorrect repair. Correcting the wiring in the plug resolved all codes.

OEM Part Supersession History

• 23104453, 23114650, 23337305 → 85073617 — Standard part evolution, likely for improved reliability or internal components.
  Heads up: The newest part number, 85073617, is the correct service replacement for all previous versions on this platform.

Model Year Variations Within This Range

• 2015-2018: While the core components and common failures are the same, there can be minor differences in fuse box layouts. For example, a YouTube repair on a 2014-2018 truck identified fuses F1, F2, F14, F15, and F17 as critical to check, while the Pass 2 data specifically called out F1 for 2017-2018 models. Always refer to the owner's manual for the specific fuse locations for your model year.
• 2015-2018: The wiring harness for installing an aftermarket brake controller is the same for all 2015-2018 Chevrolet Silverado models, indicating no significant changes to the under-dash electrical connections for the trailer brake system throughout this period.