OBD-II Code U0137: Lost Communication With Trailer Brake Control Module

What Does U0137 Mean?

The U0137 code means your vehicle's main computer lost its connection to the Trailer Brake Control Module (TBCM). This module operates the brakes on a connected trailer. Without this communication link, the vehicle cannot control the trailer's brakes, and the code is stored when expected data from the TBCM is missing for several seconds.

Technical definition: Lost Communication With Trailer Brake Control Module (TBCM). This code is set when the trailer brake data that should be received from the TBCM over the Controller Area Network (CAN) bus is missing for a specified period, typically 2-5 seconds.

Can I Drive With U0137?

Yes, But With Caution. You can drive the vehicle normally, but do not tow a trailer. The electronic trailer brakes will not function. Towing without trailer brakes increases your stopping distance by 50% or more, depending on trailer weight. This significantly overstresses the truck's brakes, leading to overheating, brake fade, and a high risk of trailer sway or jackknifing under hard braking.

Common Causes

• Blown fuse for the Trailer Brake Control Module (TBCM). (Very Common) — The TBCM is protected by one or more fuses. If a fuse blows due to a short circuit in the vehicle or trailer wiring, the module loses power and cannot communicate. This is the easiest and most important first check.
• Corroded or damaged wiring and connectors. (Very Common) — The wiring harness for the TBCM and the trailer connector at the rear of the vehicle are exposed to moisture, road salt, and physical damage. Corrosion (appearing as green powder on terminals) or a broken wire interrupts power, ground, or the CAN bus communication signal.
• Low system voltage / Weak battery. (Common) — Control modules behave erratically when vehicle voltage is low. A failing battery or alternator causes random communication codes, including U0137, to appear, especially during engine cranking.
• Damage from aftermarket accessory installation. (Common) — If accessories like a 5th-wheel hitch, aftermarket lighting, or a lift gate are installed, the wiring is often spliced into the trailer harness. An improper splice corrodes, breaks, or shorts out, causing a loss of power or communication to the TBCM.
• Software or programming issue. (Less Common) — Sometimes the problem is a software glitch causing a loss of communication. The module requires reprogramming or updating by a dealer. This is a known, documented issue on certain modern Ford and Ram models.
• Faulty Trailer Brake Control Module (TBCM). (Less Common) — The module itself fails internally due to voltage spikes, moisture intrusion, vibration, or electronic degradation over time. While possible, this should never be the first assumption without testing the wiring.
• CAN bus communication network failure. (Rare) — The TBCM communicates with other vehicle computers over the CAN bus. A broken wire, short circuit, or faulty gateway module anywhere on this network prevents the TBCM from talking to the main computer, even if the module itself is fine.
• Incorrect module installed. (Rare) — After a repair, an incorrect part is sometimes installed. For example, installing a TBCM from a 1500-series truck into a 2500/3500-series truck causes a communication failure, as the modules are not interchangeable.

Symptoms

• "Service Trailer Brake System" message. — A specific message appears on the driver information center, clearly stating there is a problem with the trailer brake system.
• Trailer brakes do not work. — When you apply the vehicle's brakes, the brakes on a connected trailer will not activate, resulting in significantly longer stopping distances.
• Manual trailer brake override does not work. — The manual slider or button on the integrated brake controller in the cab fails to activate the trailer brakes.
• Check Engine Light or ABS warning light is on. — The vehicle illuminates a warning light on the dashboard to alert the driver to the communication fault.
• Trailer brake lights stay on continuously. — The communication failure sometimes causes the trailer's brake lights to remain activated even when the vehicle's brakes are not applied.
• "Pre-Collision System Malfunction" warning (Toyota specific). — On certain Toyota models, a U0137 code links to the advanced driver-assistance systems (ADAS) and triggers a pre-collision system warning.

Diagnostic Flowchart

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

Common Fixes & Costs

• Repairing Damaged Wiring — Parts: $10-$20, Labor: $150-$400, ~2.5 hr book time (Intermediate)
• Replacing Trailer Wiring Harness Connector/Pigtail — Parts: $25-$75, Labor: $100-$200, ~1.2 hr book time (Intermediate)
  : OEM
• Module Reprogramming or Software Update — Parts: $0, Labor: $150-$250, ~1.2 hr book time (Professional)
• Replacing the Trailer Brake Control Module (TBCM) — Parts: $50-$450, Labor: $100-$300, ~1.5 hr book time (Professional)
  : OEM
  : OEM
  : OEM
  : OEM
• Diagnostic Services — Parts: $0, Labor: $100-$200, ~1.5 hr book time (Professional)

DIY vs Professional

• Replacing Trailer Wiring Harness Connector/Pigtail — Beginner: Yes
  Tools: Wire cutters, wire strippers, crimpers, heat shrink tubing, heat gun, socket set.
• Repairing Damaged Wiring — Beginner: Maybe
  Tools: Multimeter, wire cutters/strippers, soldering iron or quality butt connectors, heat shrink tubing, electrical tape.
• Replacing the Trailer Brake Control Module (TBCM) — Beginner: No
  Tools: Socket set, trim removal tools, advanced bi-directional scan tool for programming.

Used vs. New Parts: Buying Guide

When a used part is worth it: A used Trailer Brake Control Module (TBCM) only makes sense if you have a guaranteed way to program it to your vehicle. It is a cost-effective option for older trucks (pre-2013) where programming is less common or if you are an advanced DIYer with tools like FORScan (Ford) or AlfaOBD (Ram).

Donor-vehicle mileage cap: roughly under 100000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Match the OEM part number exactly. Modules for different trim levels or truck series (1500 vs 2500) are not interchangeable.
• Source from a vehicle of the same model year range.
• Avoid parts from flood-damaged or heavy-corrosion vehicles.
• Consider pre-programmed modules from reputable online sellers who flash the module to your VIN before shipping.

Decision logic:

• If The new part requires programming and you don't have the tools/expertise → Buy a new OEM part and have the dealer install/program it, or buy a pre-programmed module online.
• If You are an advanced DIYer with access to dealer-level software (FORScan, AlfaOBD) → A used module is a viable, low-cost option, but be prepared for troubleshooting.
• If The vehicle is older and the module is known to be plug-and-play (no programming needed) → A used part is a good choice with low risk.

Warranty tradeoff: Used parts from a salvage yard typically have a 30-90 day warranty, but this does not cover programming or labor costs. Aftermarket new parts often have a 1-year to limited lifetime warranty. OEM parts installed by a dealer usually carry a 1-2 year warranty.

Worst-case if a used part fails: $250-$500 if a used part is faulty or cannot be programmed. This includes the cost of the part itself plus diagnostic/labor fees from a shop that discovers it's a dud.

What Happens If You Wait — Timeline

1. Immediate: Code U0137 is set, 'Service Trailer Brake System' message appears. The TBCM is offline. (MPG impact: 0%% · Added cost: $0)
2. 0-1 month: Primary consequence is the complete inability to safely tow a trailer with electric brakes. There is no direct mechanical harm to the truck itself, but the liability and safety risk is enormous if you tow regardless. (MPG impact: 0%% · Added cost: Potential for thousands in liability, fines, or insurance claim denial if an accident occurs while towing.)
3. 1-6 months: If the root cause is a wiring short or faulty module, it creates a parasitic electrical draw, leading to a weak or dead battery, especially in cold weather. (MPG impact: 0%% · Added cost: $150-$350 for a new battery and potential tow/service call fees if the vehicle won't start.)
4. 6+ months: An ignored wiring issue worsens over time. Moisture travels up the copper wire, damaging the harness and affecting other circuits or modules that share the same power source, complicating the eventual repair. (MPG impact: 0%% · Added cost: $400-$1000+ if a simple wire repair turns into a full harness section replacement due to widespread corrosion.)

Cost of Not Fixing It

• Immediate: Inability to safely or legally tow any trailer that requires electric brakes. Your stopping distance nearly doubles, dramatically increasing the risk of a collision, especially when loaded or driving downhill. (Added cost: Potential fines for illegal towing, insurance claim denial in case of an accident, and significant liability costs if an accident causes injury or property damage.)
• Short-Term (0-3 months): No direct mechanical damage to the truck itself occurs. The primary cost is the loss of utility (cannot tow) and the persistent safety risk if you choose to tow regardless. (Added cost: $0 (unless an accident occurs))
• Long-Term (3+ months): Continued exposure to safety and liability risks. A persistent electrical short that caused the U0137 creates a parasitic draw, draining the battery over time. (Added cost: $150-$300 for a new battery if drained, plus the ever-present risk of accident-related costs.)

Diagnosis Steps

1. Check for Other Codes
   Use an OBD-II scanner to check for any other trouble codes. Other 'U' (communication) codes, especially from unrelated modules like restraints (U0151) or ABS, point to a larger network problem rather than an isolated issue with the TBCM.
   Tools: OBD-II Scanner (Beginner)
2. Inspect the Fuses
   Locate the fuse box using your owner's manual. Find all fuses labeled for 'Trailer Brake Control Module,' 'TBC,' or 'Tow.' Visually inspect each fuse to see if it's blown and replace it if necessary. A blown fuse indicates a short circuit that must be found.
   Tools: Owner's Manual, Fuse Puller or Pliers (Beginner)
3. Inspect Wiring and Connectors
   Visually inspect the trailer wiring connector at the rear bumper for signs of green corrosion, bent pins, or physical damage. Trace the wiring harness from the connector to the TBCM (often located under the vehicle near the spare tire), looking for cuts, abrasions, or damage from improper aftermarket installations.
   Tools: Flashlight (Beginner)
4. Load Test Power and Ground at the Module
   A wire can show 12V on a multimeter but fail under load due to hidden corrosion. Unplug the TBCM. Connect one side of a headlamp bulb to the power supply pin and the other to the ground pin. If the bulb lights brightly, power and ground are healthy. If it is dim or off, the wiring has high resistance and requires repair.
   Tools: Multimeter, Headlamp bulb with wires, Vehicle-specific wiring diagram (Intermediate)
5. Test the CAN Bus Network
   With the battery disconnected, measure resistance between the CAN High and CAN Low pins at the TBCM connector. A reading of 60 ohms indicates the network wiring is intact. Next, reconnect the battery and turn the ignition ON. Measure voltage: CAN High should read ~2.6V and CAN Low ~2.4V. Readings of 0V, 5V, or 12V indicate a short circuit.
   Tools: Multimeter, Vehicle-specific wiring diagram (Advanced)
6. Scan Tool Live Data Analysis
   Using a professional bi-directional scan tool, attempt to communicate directly with the TBCM. Monitor PIDs like 'TBCM Status' and 'Brake Command Output.' If the tool cannot establish communication despite confirmed good power, ground, and network wiring, the module itself has failed internally or requires a software flash.
   Tools: Advanced Bi-directional Scan Tool (Advanced)

When This Code Triggers (Freeze-Frame Conditions)

• Fault Trigger: Key-On or during network initialization (The main ECU polls all networked modules upon startup. The U0137 code is set when the TBCM fails to respond to this initial handshake within a few seconds.)
• Engine Coolant Temp: 40-200°F (Occurs at any engine temperature, from cold start to fully warmed up, as it is a communication failure, not a performance one.)
• RPM: 0 or 700-2500 (The fault logs with the key on, engine off (0 RPM), or during normal driving/idling conditions.)
• Vehicle Speed: 0-65 mph (The communication check is continuous, so the fault flags while the vehicle is stationary or at highway speeds.)

Related Codes

• U0252 — Lost Communication With Lighting Control Module Rear. These codes often appear together, especially on newer Ford trucks. If both are present, the fault is likely in a shared wiring harness or a central module (like the Trailer Module) that controls both lights and brakes. If only U0137 is present, the fault is more isolated to the brake control circuit.
• U0151 — Lost Communication with Restraints Control Module. If U0137 appears with U0151 and other U-codes from unrelated systems (e.g., HVAC, door modules), it strongly indicates a wider network problem. The issue is likely a fault in the main CAN bus wiring or the central Gateway Module, not the individual TBCM.
• C-series codes (e.g., C1112, C1114) — These are chassis codes that indicate a specific electrical fault within the TBCM system (e.g., 'TBCM Output Circuit Short to Ground'). If you have a U0137 code alongside a C-code, diagnose the C-code first. Fixing the specific circuit fault it identifies almost always resolves the general U0137 communication failure.
• U0101 — Lost Communication with TCM (Transmission Control Module). If this code is present with U0137, it points towards a more general CAN bus network issue, as both modules are critical and typically reside on the same high-speed network. The fault is typically a compromised wire shared by both modules or a failing gateway.

Climate & Environmental Factors

• Road Salt and Humidity: Vehicles operated in the salt belt (northern states and Canada) or in humid, coastal climates are significantly more prone to U0137. Salt and moisture accelerate corrosion on the trailer wiring connector, module connectors, and any splices or breaks in the harness along the vehicle's frame.
• Physical Debris: Off-road use or driving on gravel roads leads to physical damage to the wiring harness that runs along the frame rail to the rear of the vehicle, causing shorts or open circuits.

How to Talk to a Mechanic About This Code

Say this: "I have a 'Service Trailer Brake System' message and my scanner shows a U0137 code. I'd like to book a diagnostic appointment. Please start by checking fuses, load-testing the power wire, and testing CAN signals at the trailer brake module connector before recommending a module replacement."

This signals that you understand the common causes are often simple wiring or power issues, not a failed module. It directs the technician to follow a logical diagnostic path and prevents them from jumping to the most expensive conclusion.

Avoid saying:

• My check engine light is on, can you fix it?
• Just fix whatever is wrong with the trailer brakes.
• My truck says 'Service Trailer Brake System', I probably need a new module.

Questions to ask before authorizing the repair:

• What were the specific power, ground, and CAN bus voltage/resistance readings at the module connector?
• Did you perform a load test on the power feed wire to the module?
• If the module needs to be replaced, does the new one require programming and is that included in the quote?
• Can you show me the corroded wiring or damaged part before you replace it?

Where to Take It: Dealer vs Independent vs Chain

• Dealer:
  Best for: Vehicles under warranty., Known software issues or TSBs that require proprietary software (e.g., Ford TSB SSM 53236)., Complex CAN bus network diagnostics on newer vehicles., Guaranteed correct module programming.
  Downsides: Highest labor rates., May prefer to replace a whole harness section rather than repair a single wire. (Typical cost: +50% vs. baseline)
• Independent Shop: Excellent choice, especially for older trucks. A good independent auto electric specialist is often the best and most cost-effective option for finding and fixing wiring faults, which are a primary cause of U0137.
  Best for: Out-of-warranty trucks with common, well-documented issues (e.g., GM frame rail wiring rot)., Cost-effective wiring repairs and diagnosis., Shops specializing in truck or electrical systems.
  Downsides: May not have the latest diagnostic tools or software subscriptions for module programming on very new models., Quality and expertise vary widely; look for ASE certifications and good reviews on electrical work. (Typical cost: +0% vs. baseline)
• Chain Shop: AVOID for diagnosing U0137. This code requires a level of electrical and network diagnostic expertise not typically found at chain shops.
  Best for: Checking and replacing fuses., Battery testing and replacement.
  Downsides: Technicians often lack the specialized training for complex network diagnostics., High pressure to sell parts leads to misdiagnosis (e.g., recommending a new module when the wiring is bad). (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the estimated repair cost for the U0137 fault exceeds 40-50% of your truck's private-party value (e.g., from Kelley Blue Book), it's time to seriously consider selling or trading it in.

• Car worth $20000, fix is $1200: Fix it. This is a reasonable cost relative to the truck's value.
• Car worth $8000, fix is $3500: Borderline. The repair cost is approaching 50% of the vehicle's value. Get a second opinion before proceeding.
• Car worth $4000, fix is $2500: Walk away. The repair cost is over 60% of the truck's value. It's not a sound financial decision.

What Scan Tool You Need for This Code

Minimum: A tool that can read codes from all vehicle modules (ABS, BCM, IPC, etc.), not just the engine computer. It must also be able to display live data PIDs.

A basic $20 scanner only reads engine codes (P-codes) and won't see a U0137 code if it's stored in the ABS or Body Control Module. It also lacks the ability to test the CAN network or program a new module, which is often required.

Budget: BlueDriver Pro (~$100) — Reads codes from all modules, provides freeze-frame data, and graphs live data. This is sufficient to confirm the code and monitor module status, but lacks advanced functions.

Mid-range: FORScan (with adapter) or AlfaOBD (with adapter) (~$150) — These are extremely powerful PC/mobile-based tools for Ford and Ram respectively. They offer dealer-level diagnostics, read all manufacturer-specific codes, run network tests, and perform the module programming ('Proxy Alignment' for Ram) needed when installing a new TBCM.

Professional: Autel MaxiCOM MK808S or Foxwell NT510 Elite (~$350-550) — These are full-featured tablets with bi-directional control, allowing you to command the TBCM to perform self-tests. They offer comprehensive diagnostics for all makes and models and perform many service functions and programming, making them a bridge between DIY and professional tools.

Rent vs buy: For a one-time fix, paying for a professional diagnosis is often cheaper than buying a capable scanner. However, if you own a modern Ford or Ram, investing in FORScan or AlfaOBD is highly recommended for any future DIY repairs, as they are essential for many common tasks.

How to Clear the Code After You Fix It

1. Ensure all repairs (e.g., wiring fix, module replacement) are complete.
2. Reconnect the battery if it was disconnected for the repair.
3. Use a standard OBD-II scan tool to select the 'Clear/Erase Codes' function.
4. Cycle the ignition off and then on, and check if the 'Service Trailer Brake System' message or warning lights have disappeared.

Drive cycle (~20 minutes): While not always required for a 'U' code, performing a drive cycle helps ensure all systems are communicating correctly. A generic cycle involves: 1. Cold start (sit for 8+ hours). 2. Idle for 2-3 minutes. 3. Drive for 10-15 minutes with mixed stop-and-go and steady speeds (e.g., 55 mph). 4. Allow the vehicle to cool down.

Readiness monitors affected: This code does not directly affect primary emissions readiness monitors like Catalyst or O2 sensors., However, if the code triggers a general Check Engine Light, it prevents you from passing an emissions test until cleared.

Before emissions retest: drive at least 50 miles to fully set monitors.

Watch out for:

• Simply clearing the code without fixing the underlying issue (blown fuse, broken wire, faulty module) results in the code returning almost immediately.
• If a new module was installed, it must be programmed by a dealer or with advanced software *before* the code can be successfully cleared.

Will This Fail Emissions / State Inspection?

Yes — this code typically fails an OBD-II emissions inspection.

• California: An active U0137 code that illuminates the Malfunction Indicator Lamp (Check Engine Light) results in an automatic smog check failure. All OBD readiness monitors must also be set to 'Ready', which is blocked by an active communication fault.
• New York: The NYS DMV inspection includes an OBD-II scan. Any code that turns on the Check Engine Light is grounds for failure. The U0137 must be repaired and cleared before the vehicle passes.
• Texas: In counties where emissions testing is required, a vehicle fails the inspection if the Check Engine Light is on due to code U0137. The fault must be repaired for the vehicle to become compliant.

Most Commonly Affected Vehicles

• Ford F-150 (2018-2023) — Prone to wiring issues and intermittent module failures. On these trucks, it's critical to differentiate the TBM (Trailer Brake Module) from the TRM (Trailer Tow Module for lights), as they are separate components. TSB SSM 53236 notes that on 2021-2023 models, a software issue causes this code and requires a specific reset and reprogram procedure, not module replacement.
• Chevrolet Silverado 1500/2500HD (2011-2017) — Often suffers from a corroded power feed wire (red with white stripe) in the harness running along the driver's side frame rail. This leads to a loss of power at the module (Chassis Control Module Auxiliary) located near the spare tire.
• GMC Sierra 1500/2500HD (2011-2017) — Shares the same platform and wiring harness design as the Chevrolet Silverado, making it susceptible to the exact same power wire corrosion issues along the frame rail.
• Ram 1500/2500/3500 (2013-2018) — These trucks frequently experience failures of the integrated TBCM itself. A 'CF' (Configuration Fault) message on the dash display often accompanies the U0137 code. It is also a common mistake to install a module for a 1500 into a 2500/3500 (or vice versa), which causes a communication fault.
• Ford F-250/F-350 Super Duty (2011-2016) — Known for having issues with a large, loose electrical connector located above the parking brake pedal. This single point of failure causes this and many other communication codes to appear simultaneously.
• Toyota Tundra (2018-2021) — On these models, U0137 often triggers a "Pre-Collision System Malfunction" warning. The cause is sometimes an aftermarket grille emblem interfering with the radar, or the truck not having the optional trailer brake controller hardware installed, which is required for the pre-collision system to initialize correctly.
• Chevrolet / GMC Silverado / Sierra 1500/HD (2019-2024) — Newer generation trucks still suffer from wiring damage and module failures, though the specific failure points differ from the previous generation. Replacement modules are readily available.
• Honda CR-V, Pilot, Odyssey (2018-2022) — On many Honda vehicles without a factory trailer brake controller, this code is set by the ADAS (Advanced Driver-Assistance Systems) control unit, indicating a communication problem within that system, rather than a literal trailer brake issue.

Manufacturer-Specific Notes

• Ford: Per TSB SSM 53236, some 2021-2024 F-Series, Expeditions, and Rangers display a 'Trailer Brake Module Fault' and log U0137/U0252. Ford states replacing the module will NOT fix this. The correct procedure is a power-down reset of the battery and module, followed by reprogramming the Trailer Module (TRM) with the latest software. A massive recall (NHTSA Campaign 26C10) was also issued for a similar software issue on 2021-2026 models, fixable with an over-the-air or dealer software update.
• General Motors (Chevy/GMC): On 2007-2017 trucks, the TBCM is often part of the Chassis Control Module Auxiliary near the spare tire. The most common failure is the power feed wire corroding and breaking inside the harness where it runs along the driver's side frame rail. Load testing the wire is essential for diagnosis.
• Ram (Dodge): The in-dash trailer brake gain display provides extra diagnostic clues. A 'CF' message means Configuration Fault (communication loss), 'SC' means Short Circuit, and 'sb' means short to battery. Also, after installing a new TBCM, a 'Proxy Alignment' procedure must be performed with a scan tool for the new module to be recognized by the vehicle.
• Toyota: On certain Tundras, the U0137 code and a 'Pre-Collision System Malfunction' are directly linked. The system fails to initialize properly if the optional factory trailer brake controller switch and module are not installed, even if you never tow. Installing the OEM parts is often the required fix.

Real Owner Stories

2018 Ford F-150 Raptor with persistent U0137

Owner experienced a recurring "Trailer Brake Module Fault" message on the dash every time the ignition was turned on, with or without a trailer connected. The manual brake controller slider was unresponsive.

What they tried:

1. Replaced fuses and the battery with no change.
2. Replaced the in-dash TBCM gain controller switch, but the fault returned after 3 days.
3. Replaced the rear bumper 7-pin connector and cleaned all accessible ground connections.
4. Visited two different dealers; one was stumped, the other suspected a bad gain switch.

Outcome: The issue temporarily resolved after a dealer reset, but returned. A separate, intermittent cruise control issue also occurred. Because cruise control shares the CAN bus network with the TBCM, this pointed to a central Gateway Module fault rather than a trailer brake component.

Lesson: If you replace the common parts (fuses, module, switch) and the U0137 code persists, look for other seemingly unrelated electrical issues. Multiple system faults point to a central CAN bus network problem, not an individual component failure.

2011-2017 Chevrolet Silverado with "Service Trailer Brake System"

The "Service Trailer Brake System" message appeared, and a scan tool showed code U0137 in the ABS module, indicating lost communication with the TBCM (Chassis Control Module Auxiliary).

What they tried:

1. Checked fuses, which were good.
2. Attempted to communicate with the module using a scan tool but could not.
3. Tested for power at the module connector near the spare tire and found low voltage.

Outcome: A corroded and broken power wire (red with a white stripe) inside the main wiring harness along the driver's side frame rail caused the fault. Splicing in a new wire section restored power and cleared the code.

Lesson: On GM trucks of this era, a U0137 code is frequently caused by a wiring failure along the frame rail, not a failed module. Always perform a load test on the power wire at the module connector before buying a new TBCM.

2012 Ram 1500 with "CF" code on dash

The trailer brake controller display showed a "CF" (Computer Fault) error, and the truck logged a U0137 code. This also caused 4WD and traction control to show errors.

What they tried:

1. The owner knew the TBCM module itself was new and functional.
2. Initial checks of wiring and fuses revealed no obvious problems.

Outcome: The root cause was a faulty brake pedal position switch. This switch tells the computers when the brakes are applied. The plunger on the switch was not making proper contact. Replacing the brake switch permanently fixed the issue.

Lesson: On Ram trucks, a 'CF' code is a strong indicator for U0137. Before suspecting complex wiring or module issues, check the brake pedal switch, as its signal is a critical input for the trailer brake system.

2022 Ford F-150 with U0137 but NO trailer brake controller installed

A U0137 code was present in the ABS module, but the truck was not equipped with a factory trailer brake controller.

What they tried:

1. The owner was confused about why a code for a non-existent part would appear.

Outcome: According to Ford's Technical Service Bulletin (SSM 50418), this is a known software issue in the ABS module. The code should be ignored, and no repairs are necessary. The vehicle functions normally.

Lesson: Always check for TSBs related to your specific vehicle and code. A fault code is sometimes a known software glitch that doesn't indicate a real hardware problem, saving you from an expensive diagnostic chase.

How to Prevent This Code From Triggering

• Apply dielectric grease to trailer connectors. (Annually or whenever towing in wet/salty conditions.) — Dielectric grease is a non-conductive, silicone-based sealant that keeps moisture, dirt, and road salt out of electrical connectors. This prevents the corrosion that causes most wiring-related U0137 faults.
• Use a protective cover on the truck's trailer plug. (Always when not towing.) — A simple plastic or rubber cover provides a physical barrier against water, snow, and road debris, significantly reducing the chance of corrosion starting on the 7-pin connector terminals.
• Periodically inspect the wiring harness. (Every 12,000 miles or during oil changes.) — Visually check the harness running along the vehicle frame for signs of rubbing, chafing, or physical damage, especially after off-road use or if aftermarket accessories were installed. Catching a damaged wire early prevents it from breaking or shorting out.
• Ensure the vehicle battery is healthy. (Test annually after 3 years of age.) — Control modules are sensitive to low voltage. A weak battery causes unpredictable communication errors across the CAN bus, including U0137, even if the trailer brake system is perfectly fine.
• Clean grounds and apply a corrosion inhibitor. (As needed, especially in salt-belt regions.) — A poor ground connection causes intermittent power loss to the TBCM. Periodically cleaning main chassis ground points and applying a spray-on corrosion inhibitor ensures a solid connection.

Frequently Asked Questions

Is it safe to tow a trailer with the U0137 code active?

No. This code means your electronic trailer brakes are offline. Towing without functional brakes severely increases your stopping distance and causes a loss of control. It is also illegal in many jurisdictions.

Does code U0137 affect my truck's regular brakes?

No, this code is isolated to the trailer brake system. The primary hydraulic brakes of your truck will continue to function normally.

What are common mistakes when diagnosing a U0137 code?

A common mistake is immediately replacing the TBCM. Technicians often find the actual cause is a broken power wire further up the harness, a blown fuse, or a software issue requiring reprogramming. Always perform thorough wiring and power load tests before condemning the module.

Can a bad battery cause a U0137 code?

Yes, a weak battery causes low system voltage, leading to communication glitches between control modules. This triggers a U0137 code even if the trailer brake system has no actual faults. Always test the battery before beginning complex diagnostics.

My truck doesn't have a trailer brake controller, why do I have this code?

On some vehicles, like certain Ford F-150s, a software glitch causes this code to appear even if the hardware isn't installed. On other vehicles, like the Toyota Tundra, the code appears because other systems (like Pre-Collision) expect the controller to be present.

Can a problem with my trailer cause this code?

While a short in the trailer's wiring blows the TBCM fuse and causes the code, U0137 itself points to a communication failure within the truck. The code typically remains active even when no trailer is connected. A trailer-specific issue usually triggers a 'Trailer Disconnected' or 'Check Trailer Wiring' message instead.

My truck has an aftermarket trailer brake controller, can that cause the U0137 code?

Yes. If an aftermarket controller is wired incorrectly or uses an unrecognized communication protocol, the vehicle's main computers fail to see a valid TBCM and log a U0137 code. Using a vehicle-specific plug-and-play harness prevents this issue.

Will the U0137 code go away on its own?

If the cause was a temporary voltage glitch that has been resolved, the code clears itself after several drive cycles. However, if it stems from a blown fuse, broken wire, or failed module, the code remains until the part is repaired.

What's the difference between U0137 and a trailer wiring fault?

U0137 indicates a communication failure between control modules inside the truck. The main computer isn't hearing from the TBCM. A trailer wiring fault is a problem with the trailer itself or the 7-pin connector, resulting in a 'Trailer Disconnected' message.

What do 'CF', 'SC', or 'sb' mean on my Ram's trailer brake display?

These are specific diagnostic messages from the Ram integrated brake controller. 'CF' is a Configuration Fault directly related to U0137. 'SC' is a Short Circuit to ground, and 'sb' indicates a Short to Battery on the brake output wire.

Can I install an OEM trailer brake controller myself to fix this?

On some vehicles like the Toyota Tundra, installing the OEM controller fixes the missing hardware code. On Ram or Ford trucks, the vehicle's computer must also be programmed using a dealer tool or software like AlfaOBD/FORScan. Without this programming, the U0137 code remains active.

Key Takeaways

• Code U0137 indicates a total communication loss with the Trailer Brake Control Module, instantly disabling your electronic trailer brakes.
• Towing a heavy trailer with this active code increases stopping distance by up to 50%, creating a severe jackknife risk.
• Check the 7-pin bumper connector and dedicated TBCM fuses first, as corrosion and blown fuses cause the majority of U0137 faults.
• Never replace the TBCM without load-testing its power wire first; a corroded frame-rail wire mimics a dead module perfectly.
• On 2021-2024 Ford and Ram trucks, U0137 is frequently a software glitch requiring a 1-hour dealer flash rather than a $400 hardware replacement.