U0415 on 2015-2019 Chevrolet Silverado 2500: Causes and Fixes

What's Unique About the 2015-2019 Chevrolet SILVERADO 2500

For this generation of Silverado HD trucks (K2XX Platform), the U0415 code is uniquely and strongly tied to several well-documented issues. Most notably, as outlined in GM Technical Service Bulletin #PIT5490B, the code is frequently triggered by a low brake fluid level, which causes the fluid to slosh during maneuvers and momentarily trip the level sensor. This sends 'invalid' data that other modules flag. Additionally, this platform is known for specific wiring harness issues. TSB #PIT5288H points to a chafe point near the park brake pedal bracket, and TSB #PIT5457D identifies corrosion-prone splices in the harness running under the driver and passenger sill plates due to water intrusion.

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)
• "Service StabiliTrak" message
• ABS warning light illuminated
• Traction Control System (TCS) light illuminated
• Inoperative trailer brakes
• Message appears intermittently, often during turns, hard braking, or acceleration.
• In some cases with related wiring faults, other electrical issues like inoperative wipers, a dead battery, or loss of reverse camera may occur.

Most Likely Causes

1. Low Brake Fluid Level 🔴 High Probability → Shop Brake Fluid As documented in TSB #PIT5490B, the brake fluid level sensor is very sensitive. During turns, acceleration, or braking, fluid sloshing in a partially-filled reservoir can momentarily trigger the 'low level' sensor. The EBCM reports this, and the Chassis Control Module flags it as invalid data, setting U0415 and displaying the 'Service Trailer Brake' message.
   How to confirm: Visually inspect the brake fluid level in the master cylinder reservoir. A scan tool can also monitor the 'Brake Fluid Level Sensor' parameter in the EBCM data list, which will read 'Low' or 'OK'.
   Typical fix: Top off the master cylinder with the correct DOT brake fluid to the 'MAX' line. It is also critical to inspect for brake fluid leaks or worn brake pads, as these are common reasons for a low fluid level. If no external leaks are found, inspect the rear of the master cylinder for leaks into the brake booster.
   Est. part cost: $5-$15
2. Damaged or Pinched Wiring Harness 🟡 Medium Probability GM has issued multiple TSBs for this platform regarding wiring issues. TSB #PIT5288H points to the dash harness being pinched by the left instrument panel mounting bracket, near the park brake pedal. TSB #PIT5457D identifies potential damage or corrosion to the harness and splice packs running under the driver and passenger sill plates, often due to water intrusion.
   How to confirm: Visually inspect the wiring harnesses in the locations specified by the TSBs. For PIT5288H, look for a pinched harness near the park brake pedal bracket from underneath the dash. For PIT5457D, remove the plastic sill plates and peel back the carpet to inspect the wiring channel for signs of moisture or blue/green corrosion on the wires or in splice connectors.
   Typical fix: Repair the damaged section of the wire harness. This may involve splicing wires, replacing terminals, cleaning corrosion, and re-routing or protecting the harness with anti-abrasion tape to prevent future damage.
   Est. part cost: $10-$50
3. Failing Battery or Poor Ground Connection ⚪ Low Probability → Shop Vehicle Battery Low system voltage during cranking or from a weak battery can cause multiple control modules to receive erratic data or lose communication, setting a variety of 'U' codes, including U0415. A corroded main EBCM ground connection on the frame can also cause this. On many GM trucks, a key ground point is located on the frame rail under the driver's door. A Reddit user fixed a similar issue by cleaning a corroded ground for the trailer brake control module near the spare tire.
   How to confirm: Test the battery's state of charge and health with a load tester. Check the main power and ground connections for tightness and corrosion. Specifically, locate and inspect the main ground points on the frame under the driver's side and near the rear of the vehicle for the trailer brake system.
   Typical fix: Replace a weak or failing battery. Disassemble, clean, and secure corroded ground connections. Applying dielectric grease can help prevent future corrosion.
   Est. part cost: $150-$300

Rare But Worth Checking

• Faulty Trailer Brake Control Switch: → Shop Trailer Brake Control Module The manual trailer brake gain/activation switch assembly on the dashboard can fail internally, sending erratic signals. This is a common enough issue that Dorman produces a replacement circuit board (Part #601-237) to avoid replacing the entire assembly. Several owner forums and videos report success with this specific repair.
• Faulty Electronic Brake Control Module (EBCM): → Shop ABS Control Module While possible, module failure is less common than wiring or fluid level issues. A faulty EBCM may send corrupt data without any external cause. This should only be considered after all wiring, power, and ground checks have been completed.
• Faulty Trailer Brake Control Module (TBCM): → Shop Trailer Brake Control Module The separate Trailer Brake Control Module, located above the spare tire, can also fail. This module communicates with the EBCM and can be a source of the fault. One owner on YouTube documented replacing this module to fix the issue after checking wiring.
🎬 Watch this walkthrough on replacing the trailer brake control module.

Diagnosis Steps

1. Read all Diagnostic Trouble Codes (DTCs) from all modules using a professional scan tool.
2. Check the brake fluid level in the master cylinder. If it is not at the 'MAX' line, top it off with the correct DOT fluid. Clear the codes and perform a road test with turns and stops to see if the code returns.
3. If the fluid was low, inspect the brake system for leaks or worn pads to determine the cause of the fluid loss.
4. If the code returns, inspect the wiring harness at the known problem areas: under the driver and passenger sill plates for blue/green corrosion (TSB #PIT5457D) and in the left instrument panel area near the park brake pedal for pinching (TSB #PIT5288H).
5. Inspect the main EBCM connector for corrosion, moisture, or backed-out pins.
6. Test the vehicle's battery and charging system to rule out low voltage as a cause.
7. Inspect and clean the main chassis ground points, particularly the one located on the frame under the driver's door and any related to the trailer brake system near the rear of the vehicle.
8. If the 'Service Trailer Brake' message is the primary symptom, consider testing or replacing the manual trailer brake control switch in the dashboard, as this is a known failure point.
9. If all wiring, grounds, and fluid levels are confirmed good, the issue may be with the Trailer Brake Control Module (above the spare tire) or the EBCM itself. Further diagnosis with an advanced scan tool to monitor data packets would be required.

Parts You'll Likely Need

• Brake Fluid — The most common fix is simply topping off the brake fluid reservoir to resolve a false 'low level' signal.
  Trusted brands: ACDelco, Prestone
  OEM price range: $10-$20
  Aftermarket price range: $5-$15
• Trailer Brake Control Switch (OEM #84109433 (Verify by VIN)) — The manual switch on the dash is a known failure point, causing erratic signals. It can often be replaced without changing the entire Trailer Brake Control Module.
  Trusted brands: ACDelco, Dorman
  OEM price range: $50-$85
  Aftermarket price range: $30-$60

Related Codes That Often Appear With This One

• U0077 — Often appears with U0415 in cases of wiring harness damage, as noted in TSBs #PIT5288H and #PIT5457D, indicating a general CAN bus communication failure with the Chassis Control Module.
• U0121 — Lost Communication With Anti-Lock Brake System (ABS) Control Module. This code may appear alongside U0415, indicating a more severe communication breakdown with the EBCM, often related to the sill plate wiring corrosion per TSB #PIT5457D.
• U0126 — Lost Communication With Steering Angle Sensor (SAS) Module. This can be set due to the same wiring harness issues (per TSB #PIT5288H) that cause U0415.
• C1117 — A YouTube video creator noted that replacing the faulty manual trailer brake switch also resolved a C1117 DTC.

Technical Service Bulletins (TSBs) & Recalls

• PIT5490B
• PIT5288H
• PIT5457D

Platform-Specific Known Issues

• TSB #PIT5490B: Documents that a 'Service Trailer Brake' message and U0415 can be set simply by the brake fluid level being near the minimum mark. The fix is to fill the reservoir to the maximum level.
• TSB #PIT5288H: Warns of a pinched wire harness in the left instrument panel area by the park brake bracket that can cause U0415 and a wide range of other communication and electrical fault codes.
• TSB #PIT5457D: Points to potential open, damaged, or corroded wiring (specifically Communication Enable circuit 5986) in the harness under the driver and passenger sill plates, leading to communication loss with the EBCM and other modules.

Mechanic-Grade Diagnostic Values

• CAN Bus Network Resistance — expected: ~60 Ω. Failure: A reading of ~120 Ω indicates an open circuit or a terminating module is offline. A reading significantly less than 60 Ω (e.g., ~40 Ω) suggests an extra terminating resistor or a shorted module on the bus.
• Trailer Brake Control Switch 5V Reference — expected: 4.8-5.2 V. Failure: Voltage outside this range indicates a problem with the TBCM's reference output or a short in the harness.
• Trailer Brake Control Switch Low Reference Circuit — expected: < 5 Ω to ground. Failure: Resistance higher than 5 Ω indicates an open or high resistance in the ground circuit for the switch.

Hidden / Shadow Codes Worth Checking

• Symptom Byte (e.g., U0415 5A): GM uses a two-character symptom byte after the primary DTC to provide more specific information. For example, '5A' indicates a 'Plausibility Failure,' meaning the data from the EBCM is technically valid but doesn't make sense in the current context (like the brake fluid level sensor flapping between 'OK' and 'Low' rapidly). '08' indicates 'Signal Invalid'. Seeing these requires a scan tool that can read manufacturer-specific codes. (see via GM GDS2/Tech2 or other professional-grade scan tools.)

Scan Tool Commands That Help

• GDS2: EBCM Data List > Brake Fluid Level Sensor — As per TSB #PIT5490B, this is the first step after reading codes. It allows you to see in real-time if the sensor is reading 'Low' or 'OK', confirming if fluid slosh is the root cause.
• GDS2: Trailer Brake Control Module > Output Test — This command manually activates the trailer brake output from the TBCM. It's used to verify if the module itself can generate a signal, helping to isolate the problem between the module, wiring, or the dash switch.
• Trailer Simulator Tool: Load Circuit Test — This specialty tool, mentioned in GM bulletin PIT5509, connects to the 7-pin connector and uses actual brake magnets to simulate a trailer's electrical load. It is the definitive way to determine if the fault lies within the truck's system or the trailer's wiring, as the truck may not send voltage unless a proper load is detected.

Wiring & Ground Locations

• Main EBCM Ground — On the frame rail, directly under the driver's side door.. This is the primary ground for the Electronic Brake Control Module. Corrosion or looseness here can cause erratic EBCM behavior and a host of communication codes, including U0415.
• G218 — Under the driver's side dash, behind the kick panel or sill plate trim.. This is a major interior ground point. It is referenced in TSB #PIT5457D as a location prone to corrosion from water intrusion, affecting CAN bus communication and causing codes like U0415.
• G103 — On the cowl in the rear of the engine compartment, or on a cylinder head. It grounds the BCM, Instrument Panel Cluster (IPC), and Data Link Connector (DLC).. A poor connection at G103 can disrupt the Body Control Module or other key modules that need to communicate with the EBCM, leading to network codes.
• G401 — On the rear frame rail, often near the spare tire.. This is a primary ground point for rear-body components, including the Trailer Brake Control Module (TBCM) and trailer lighting circuits. Corrosion here is a common cause of 'Service Trailer Brake' messages.
• EBCM Connector (X1) — The main 38-pin harness connector at the Electronic Brake Control Module.. Testing for power, ground, and CAN bus signals directly at this connector is essential for advanced diagnosis. Pinout diagrams are required to test specific circuits like the High Speed LAN (pins 22 & 23 on some models) or power/ground inputs.

Real Owner Repair Stories

• eTrailer Q&A Forum (2015 Chevrolet Silverado 3500) — Trailer brakes not working, no power at trailer connector, no DIC messages.
  ❌ Tried (didn't work) Replaced the dash trailer brake controller switch., Replaced the trailer brake control module (TBCM) on the frame.
  ✅ What actually fixed it The expert diagnosis pointed to a blown fuse (#1 in the engine bay fuse block) or an open in the power supply wire leading to the controller. This highlights the need to check basic power supply before replacing expensive modules.
• Reddit user /u/bbbbbraddddd (2015 Silverado 1500) — Stabilitrak warning, radio and AC randomly shutting off and turning back on.
  ❌ Tried (didn't work) Checking grounds in the engine bay.
  ✅ What actually fixed it The owner found and fixed a bad ground connection under the dash where insulation was interfering with the connection. This is likely ground G218, a known issue that causes widespread CAN bus problems.
• Chevrolet Forum user 'ragtoptempest' (2015 Silverado 2500) — Trailer brakes not working, but all trailer lights work. No codes or messages on the dash.
  ❌ Tried (didn't work) Changing the plug on the trailer., Checking all fuses and connections for corrosion.
  ✅ What actually fixed it The issue was not fully resolved in the thread, but an expert noted that an underlying ABS issue can disable the trailer brake system even if no trailer-specific codes are present, pointing the owner towards a deeper ABS system diagnosis rather than continuing to focus only on the trailer circuits.

When the Usual Fixes Don't Work

• While wiring and fluid are common causes, multiple owner reports exist where the problem persisted after checking them. In one case, a 2015 Silverado 3500 owner replaced both the dash switch and the frame-mounted TBCM module, but the problem was ultimately traced to a lack of power from a blown fuse or an open in the supply wire. This underscores the importance of verifying basic power and ground circuits with a multimeter before condemning expensive control modules, even when they are known to fail.

OEM Part Supersession History

• 22822675 → 84109433 — Part revision or manufacturer change for the dashboard-mounted Trailer Brake Control Switch.

Model Year Variations Within This Range

• 2014-2016 vs 2017-2019: The underhood fuse box relay for the trailer brake controller is in the same physical location but has a different number. For 2014-2016 models, it is relay #64. For 2017-2019 models, it is relay #63.
• 2017 (specific VINs): A small batch of 2017 models from the Ft. Wayne plant may have defective, improperly hardened ground bolts that fail to provide proper clamping force, leading to intermittent electrical issues per TSB #PIT5562.