C1113 on 2014-2018 Chevy Silverado 1500: Trailer Brake System Fault Explained

What's Unique About the 2014-2018 Chevrolet SILVERADO 1500

On this generation of Silverado (K2XX platform), the trailer brake control system is notoriously sensitive to the vehicle's main battery voltage. GM issued multiple Technical Service Bulletins (TSBs) advising technicians to test the battery's health *before* performing any other diagnostics for this code. Additionally, the Trailer Brake Power Module (officially known as component K133) is located on a frame crossmember above the spare tire, making its electrical connector highly susceptible to corrosion from road spray, a well-documented cause of this fault.

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 connection is not recognized by the truck
• Integrated trailer brake controller is inoperative
• Slow engine crank may be noticed (symptom of a weak battery)

Most Likely Causes

1. Weak or Failing Vehicle Battery 🔴 High Probability As documented in TSBs PIT5521A and PIT5529A, the control modules on this platform are extremely sensitive to low voltage, which can trigger faults during events like engine cranking. This is the number one recommended check by GM.
   How to confirm: Test the battery's state of health with a professional-grade load tester, such as the Midtronics GR8 mentioned in GM bulletins. A simple voltage check is often not sufficient to identify a weak battery.
   Typical fix: Replace the vehicle's battery. Ensure the new battery is fully charged before installation and that all terminals are clean and tight. Many owners have confirmed this fix in forums after other failed attempts.
   Est. part cost: $150-$350
2. Corroded Trailer Brake Power Module (TBPM) Connector 🔴 High Probability The module (also known as K133) is located on the frame directly above the spare tire, exposing its connector to water, salt, and dirt. TSB PIT5529A specifically notes that water can enter if a cavity plug is missing or dislodged, and that 'connector hydro-locking' can force these plugs out during connection.
   How to confirm: Lower the spare tire for access. Disconnect the module's electrical connector (with the key off) and visually inspect the pins and connector housing for green or white corrosion or any signs of water intrusion.
   Typical fix: If corrosion is minor, clean the terminals with a specialized contact cleaner and a small brush. If severe, the connector pigtail must be replaced. Apply dielectric grease liberally upon reassembly to prevent future moisture intrusion.
   Est. part cost: $25-$150
3. Corroded or Damaged 7-Pin Trailer Connector 🟡 Medium Probability The rear bumper connector is constantly exposed to the elements, leading to corrosion inside the plug which can cause shorts or open circuits. The system is very sensitive to resistance changes.
   How to confirm: Visually inspect the pins inside the truck's 7-pin socket for corrosion or damage. Test with a known-good trailer or a 7-pin circuit tester to see if the fault disappears.
   Typical fix: Clean the terminals or replace the 7-pin socket assembly if it's damaged. GM released an updated part with a stronger door spring to hold the trailer plug more securely.
   Est. part cost: $20-$70
4. Faulty Trailer Brake Control Module (TBCM/TBPM) ⚪ Low Probability While the module can fail internally, it is often replaced unnecessarily when the actual cause is a bad battery or corroded wiring. It should be the last part replaced after all other causes are ruled out.
   How to confirm: This is typically a process of elimination. If the battery, all connectors, and wiring have been confirmed to be in good condition through visual inspection and multimeter testing, the module itself is the likely culprit.
   Typical fix: Replace the Trailer Brake Power Module (GM Part #85073617). Note that a new module may require programming by a dealer or a qualified shop with a GM scan tool.
   Est. part cost: $60-$150

Rare But Worth Checking

• Faulty In-Dash Trailer Brake Control Switch: The manual control switch on the dashboard (GM Part #84108373) can fail internally, sending incorrect signals. Some owners have reported 🎬 Watch: How to replace the in-dash control switch fixing the issue by replacing this switch, but it is far less common than battery or corrosion issues.

Diagnosis Steps

1. Read all Diagnostic Trouble Codes (DTCs) from all vehicle modules.
2. CRITICAL: Thoroughly test the vehicle's battery state of health using a professional electronic tester (e.g., Midtronics GR8). Do not proceed until you have confirmed the battery is good. Address any battery or charging system issues first.
3. If the battery is good, turn the ignition off. Lower the spare tire to gain access to the Trailer Brake Power Module (TBPM) on the frame crossmember.
4. Disconnect the main electrical connector from the TBPM. Carefully inspect both the module's pins and the connector's terminals for any signs of green or white corrosion, moisture, or backed-out pins.
5. Check that all cavity plugs are present and fully seated in the connector to prevent water intrusion, as specified in TSB PIT5529A.
6. If corrosion is found, clean thoroughly with electrical contact cleaner. If damage is severe, replace the connector pigtail. Apply dielectric grease before reconnecting.
7. Inspect the truck's 7-pin trailer connector at the bumper for corrosion or damage.
8. If all connectors and wiring appear clean and undamaged, test the power and ground circuits to the TBPM using a multimeter to ensure proper voltage and low resistance to ground (less than 5 ohms).
9. If all wiring, connectors, and the battery check out, the Trailer Brake Power Module (Part #85073617) itself is the most likely remaining cause of the fault.

Parts You'll Likely Need

• Vehicle Battery — The trailer brake system is highly sensitive to low voltage, and a weak battery is the most common cause of this code, as per multiple GM TSBs.
  Trusted brands: ACDelco, Interstate, DieHard
  OEM price range: $200-$350
  Aftermarket price range: $150-$250
• Trailer Brake Power Module (OEM #85073617 (supersedes 23104453, 23114650, 23337305)) — The module can fail internally or its pins can be damaged by corrosion due to its location above the spare tire. It is the component that sets the code.
  Trusted brands: ACDelco (GM Genuine)
  OEM price range: $80-$150
  Aftermarket price range: $60-$100
• Trailer Brake Power Module Connector Pigtail (OEM #ACDelco PT2715) — This connector is prone to corrosion. If the terminals are damaged, the connector itself must be replaced by splicing in a new pigtail.
  Trusted brands: ACDelco, Dorman (e.g., 645-511)
  OEM price range: $40-$80
  Aftermarket price range: $20-$50
• In-Dash Trailer Brake Control Switch (OEM #84108373 (supersedes 23145874)) — A rare but possible cause. The switch assembly on the dashboard can fail, leading to the service message. It is a less likely failure point than the battery or rear module/connector.
  Trusted brands: ACDelco (GM Genuine)
  OEM price range: $50-$90
  Aftermarket price range: $30-$60

Related Codes That Often Appear With This One

• C1112 — This code is for a fault in the trailer brake control relay low control circuit and is often set along with C1113 due to the same root causes like low voltage or corrosion, as noted in TSB PIT5529A.
• C1114 — This code relates to the trailer brake control solenoids control circuit and shares the same power and ground sources, making it susceptible to the same electrical issues.
• C111B — Another related trailer brake system code that GM groups with C1113 in its service bulletins for the same diagnostic procedure (check battery first).
• U1556 — A communication network code that can appear with the C-codes when low voltage or corrosion affects the module's ability to communicate.
• U1505 — Another communication code often triggered by the same electrical faults as the other trailer brake codes, listed in TSB PIT5529A.

Technical Service Bulletins (TSBs) & Recalls

• PIT5529A: The most comprehensive TSB for this issue. It combines previous bulletins and identifies the two primary causes as low battery voltage and water/dirt intrusion into the Trailer Brake Power Module (K133) connector due to missing or dislodged cavity plugs. It specifically warns about 'connector hydro-locking' pushing plugs out.
• PIT5521A: This bulletin specifically advises technicians to check the battery's state of health with a Midtronics GR8 tester *before* performing any other diagnostics for codes C1112, C1113, C1114, and C111B, noting that a slow engine crank can be a related symptom.
• PIT5529: The predecessor to PIT5529A, which first officially documented the issue of corrosion in the Trailer Brake Power Module connector as a cause for these DTCs.

Platform-Specific Known Issues

• Owner Experience: The Battery is the Real Culprit: Many owners have shared experiences of chasing the C1113 code by replacing the in-dash switch or the trailer brake module itself, only to find the problem persists. A significant number of these stories end with the o

Mechanic-Grade Diagnostic Values

• Ground Circuit Resistance at TBPM Connector (X411) — expected: Less than 5.0 ohms. Failure: A reading higher than 5.0 ohms indicates high resistance or an open in the ground circuit.
• Voltage Drop on Ground Circuit at TBPM Connector (X411) — expected: Less than 0.3 Volts. Failure: A reading higher than 0.3V points to high resistance in the ground circuit, possibly from a corroded frame ground.
• Solid State Relay Enable Circuit Voltage (Pin 33 at X411) — expected: DTC C1113 is defined as a short to voltage on this circuit. Normal voltage varies, but it should not be shorted to battery voltage.. Failure: A reading near battery voltage on this circuit indicates a short to power.
• Operating Voltage Range — expected: 9.5-17 Volts. Failure: The module may set fault codes if the system voltage drops below 9.5V, especially during engine cranking.

Scan Tool Commands That Help

• GDS2: Data Display > Trailer Brake Type — Use this to see how the Chassis Control Module (CCM) or Brake System Control Module (BSCM) is identifying the connected trailer (or tester). It can show "Electro-magnetic", "Electro-over hydraulic brakes", or "Undefined". This helps confirm if the truck is correctly detecting a trailer.
• GDS2: Data Display > Trailer Brake Control Output Circuit — This parameter shows the real-time status of the output circuit (Circuit 47). It will display "Okay", "Short to Ground", "Short to Power", or "Unknown". This is useful for diagnosing codes like C1114 which often appear with C1113.

Wiring & Ground Locations

• K133 / X411 — The Trailer Brake Power Module (K133) is located on the frame crossmember, directly above the spare tire. Its main electrical connector is designated X411.. This is the most common location for corrosion-related failures due to its exposure to road spray and debris. All power, ground, and control signals for the trailer brake system pass through this connector.
• Pin 33 at X411 — Pin 33 at the Trailer Brake Power Module connector (X411). The wire is typically Yellow with a Black stripe (YE/BK).. This is the specific 'Solid State Relay Enable' circuit. DTC C1113 is set when the module detects a short to voltage on this exact pin/circuit.
• Pin 32 at X411 — Pin 32 at the Trailer Brake Power Module connector (X411). The wire is typically Red with a White stripe (RD/WH).. This is the main Battery Positive Voltage feed for the module. A loss of power on this pin, or high resistance, will cause multiple system faults.
• Underhood Fuse Block — Located on the driver's side of the engine bay, near the master cylinder.. Contains multiple fuses critical to the trailer brake system, including fuses for 'Trailer B+' (Trailer Battery) and the trailer brake control module itself. A blown fuse here can be the root cause of the issue.

Real Owner Repair Stories

• YouTube channel '59 Motorsports' (2014-2018 GM Truck (specific year not mentioned)) — "Service Trailer Brake" message on the dashboard.
  ❌ Tried (didn't work) Replacing the in-dash trailer brake control switch module.
  ✅ What actually fixed it After replacing the in-dash switch did not solve the problem, the owner inspected the underhood fuse box. They found that the 30-amp fuse in position #2 for the 'Trailer Battery' was blown. Replacing this fuse cleared the 'Service Trailer Brake System' message.
• YouTube user comment on 'Shaners Mechanic Life' video (2018 Silverado) — Service Trailer Brake System warning.
  ❌ Tried (didn't work) Replacing the in-dash switch with an AC Delco part., Replacing the Trailer Brake control module., Confirming all fuses were good., Confirming power and ground to both the auxiliary and main trailer brake modules., Confirming the 7-pin socket was good with no corrosion or wire breaks.
  ✅ What actually fixed it The user reported being 'baffled' as all common fixes failed. The only remaining component they had not replaced was the 'auxiliary control module', implying a more complex and unresolved issue possibly related to a secondary module in the system. This highlights an edge case where common fixes are not sufficient.

OEM Part Supersession History

• 23104453, 23114650, 23337305 → 85073617 — These are previous part numbers for the Trailer Brake Power Module that have been consolidated into the latest part number, 85073617. This is common as GM updates parts to improve reliability or for manufacturing changes.