U0415 on 2015-2019 GMC Sierra 2500: Causes for Invalid ABS Data and Fixes

What's Unique About the 2015-2019 Gmc SIERRA 2500

On the K2XX generation of GM trucks (2014-2019), this network communication code is uniquely tied to several well-documented issues that are not a failed computer. A specific GM Technical Service Bulletin (PIT5490B) points directly to low brake fluid causing this code during turns or hard braking as fluid sloshes in the reservoir. 🎬 Watch: How low brake fluid triggers the service trailer message. Other bulletins highlight known weak points in wiring harnesses, such as under the driver/passenger sill plates (PIT5457D) and a pinch point for the main dash harness behind the instrument panel near the parking brake pedal 🎬 See this walkthrough on finding and repairing pinched dash wiring. (PIT5288H), which are prone to damage and can cause this and other communication codes.

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).
• ABS warning light illuminated.
• Traction control or StabiliTrak warning light illuminated, sometimes with a "Service Stabilitrak" message.
• Cruise control may be disabled.
• Intermittent loss of trailer brake function.
• HVAC (Heater-Vent-Air Conditioning) display may go blank. [PIT5405A]
• In severe cases related to dash wiring damage, other symptoms like "No Fob Detect," no audio, or a dead battery can occur.

Most Likely Causes

1. Low Brake Fluid Level 🔴 High Probability → Shop Brake Fluid A GM Technical Service Bulletin (PIT5490B) explicitly states that brake fluid sloshing in a low reservoir during turns, acceleration, or braking can cause the level sensor to send a momentary 'low' signal. The EBCM sends this data to the Chassis Control Module, which flags it as invalid and sets U0415, triggering the "Service Trailer Brake" message.
   How to confirm: Visually inspect the brake fluid level in the master cylinder reservoir. If it is near or below the 'MIN' line, this is the likely cause. A professional scan tool (like GDS2) can monitor the 'Brake Fluid Level Sensor' parameter in the EBCM data list, which will read 'Low' when the fault occurs.
   Typical fix: Fill the master cylinder reservoir to the 'MAX' line with the correct DOT 3 or DOT 4 brake fluid. It is critical to also inspect for the cause of the low fluid, such as worn brake pads (most common reason) or a leak in the brake system, including the rear of the master cylinder.
   Est. part cost: $5-$15
2. Damaged or Corroded Wiring Harness 🟡 Medium Probability Multiple TSBs point to specific areas. TSB #PIT5457D notes wiring under the driver and passenger sill plates can corrode or break, specifically affecting the Communication Enable circuit 5986. TSB #PIT5288H identifies a pinch point for the main instrument panel harness between a metal mounting bracket and the body, near the parking brake pedal. [PIT5288H]
   How to confirm: Visually inspect the wiring harnesses in the locations mentioned in the TSBs. For sill plates, remove the plastic trim and look for green corrosion or broken wires. For the dash, inspect from underneath for a pinched harness near the large metal bracket to the left of the steering column. A multimeter can be used to check for voltage on circuit 5986 at the EBCM connector.
   Typical fix: Repair the damaged section of the wire harness. This involves cutting out the damaged section, splicing in a new piece of wire using approved crimp connectors, and protecting the repair with heat shrink tubing. GM advises against soldering for most wiring repairs. For the pinched dash harness, it must be freed, repaired, and rerouted to prevent future damage.
   Est. part cost: $10-$50
3. Faulty Trailer Brake Control Module (TBCM) ⚪ Low Probability → Shop Trailer Brake Control Module The TBCM, located near the spare tire, is exposed to road salt and moisture, which can lead to internal failure or corroded connections, causing communication issues.
   How to confirm: After confirming power and ground to the module and verifying the integrity of the wiring harnesses, a technician would use a scan tool to attempt communication. If the module has power but doesn't communicate, it is likely faulty.
   Typical fix: Replace the Trailer Brake Control Module. The replacement module must be programmed to the vehicle's VIN using dealership-level software like GM's SPS (Service Programming System).
   Est. part cost: $150-$300
4. Poor Connection at EBCM or BCM ⚪ Low Probability Vibrations and moisture can lead to poor connections at the main control modules. TSB #PIT5405A suggests checking the Body Control Module (BCM) connections when multiple communication codes are present. Water intrusion into the EBCM connector is also a known, though less common, issue.
   How to confirm: Disconnect the electrical connectors at the Electronic Brake Control Module (EBCM) and Body Control Module (BCM). Inspect for corrosion (green or white powder), bent pins, or loose-fitting terminals.
   Typical fix: Clean the connector pins with electrical contact cleaner and a small brush. Apply a small amount of dielectric grease before reconnecting securely to prevent future moisture intrusion.
   Est. part cost: $5-$10

Rare But Worth Checking

• Poor Battery/Ground Connections: → Shop Vehicle Battery
• Faulty Brake Fluid Level Sensor: → Shop Brake Fluid

Diagnosis Steps

1. Read all Diagnostic Trouble Codes (DTCs) from all modules using a professional scan tool that can access chassis and network codes.
2. Check the brake fluid level in the master cylinder. If low, top it off with the specified fluid. Crucially, inspect brake pads for wear, as this is the most common cause of a gradually dropping fluid level. Clear codes and re-test by driving.
3. If fluid is OK, consult TSBs PIT5490B, PIT5457D, and PIT5288H.
4. Remove the driver and passenger front door sill plates and peel back the carpet to inspect the wiring harness channel for signs of water intrusion, corrosion (especially green wires), or broken wires, as noted in TSB #PIT5457D.
5. Inspect the wire harness behind the left side of the instrument panel, near the parking brake pedal assembly, for pinching against the metal dash support bracket, as noted in TSB #PIT5288H. [PIT5288H]
6. Inspect the electrical connector and wiring at the Trailer Brake Control Module (TBCM), located above the spare tire, for corrosion or damage.
7. Perform loaded voltage drop tests on the power, ground, and communication enable (Circuit 5986) wires at the EBCM to ensure the module has proper electrical supply under load.
8. If all wiring and connections are confirmed good, the issue may be with a control module. Further diagnosis with a scan tool would be needed to isolate a faulty TBCM or, less likely, the EBCM itself.

Parts You'll Likely Need

• Brake Fluid — This is the most common and simplest fix, as low fluid level is a known cause for this code on this platform per TSB PIT5490B.
  Trusted brands: ACDelco, Prestone
  OEM price range: $10-$20
  Aftermarket price range: $5-$15
• Trailer Brake Control Module (OEM #20964299) — If wiring and fluid levels are good, the module itself can fail due to its exposed location, causing communication errors. Note: Part number 20964299 is listed for 2013-2014 models; always verify the correct part number with the vehicle's VIN for later years as it may differ.
  Trusted brands: ACDelco, Dorman
  OEM price range: $200-$300
  Aftermarket price range: $150-$250
• Wire Splice Connectors — Needed for repairing corroded or broken wires found in the sill plate or dash harnesses. GM recommends using specific crimp-style connectors, not solder.
  Trusted brands: 3M, Dorman
  OEM price range: $2-$5 per connector
  Aftermarket price range: $5-$15 for a kit

Related Codes That Often Appear With This One

• U0077 — Indicates a High Speed Communication Bus issue, often related to the wiring problems described in TSBs PIT5288H and PIT5457D.
• U0121 — Indicates Lost Communication With Anti-Lock Brake System (ABS) Control Module, a more severe version of the fault that can accompany U0415, often pointing to a complete break in the wiring.
• U0126 — Indicates Lost Communication With Steering Angle Sensor Module, which is on the same network and can be affected by the same wiring faults. (TSB #PIT5288H, #PIT5457D)
• U0140 — Indicates Lost Communication With Body Control Module (BCM), pointing to a wider network failure, often related to the dash or sill plate harness issues. (TSB #PIT5405A)

Technical Service Bulletins (TSBs) & Recalls

• PIT5490B: Links U0415 and a 'Service Trailer Brake' message to low brake fluid level.
• PIT5457D: Points to damaged/corroded wiring (specifically circuit 5986) under the sill plates as a cause for loss of communication codes, including U0415.
• PIT5288H: Identifies a pinched wire harness in the instrument panel as a cause for U0415 and other electrical faults.
• PIT5405A: Suggests checking the BCM when U0415 is present with other codes and a blank HVAC display.
• 22-NA-034: Addresses various electrical issues caused by poor battery cable connections or a bad BCM ground (G218).

Platform-Specific Known Issues

• A "Service Trailer Brake" message accompanied by DTC U0415 is frequently caused by the brake fluid level being near the minimum mark. Topping off the fluid is the specified first check per TSB #PIT5490B.
• Damaged or corroded wiring in the harness that runs under the driver and passenger sill plates is a known issue that can cause a loss of communication with the EBCM and other modules. This often affects the Communication Enable Circuit 5986. (TSB #PIT5457D)
• A pinched wire harness behind the left side of the instrument panel, near the parking brake pedal, can cause a host of electrical issues, including setting code U0415. (TSB #PIT5288H)

Mechanic-Grade Diagnostic Values

• Communication Enable Circuit 5986 Voltage — expected: Approximately 12 Volts when the BCM is awake (ignition in ACC, ON, or START).. Failure: Low or no voltage indicates an open, short, or high resistance in the circuit. The circuit should be able to light a small 194 bulb (drawing ~250mA) with at least 11 volts measured across the bulb.
• CAN Bus Network Resistance — expected: Approximately 60 Ohms when measured between the High-Speed GMLAN High and Low pins at the DLC (Pins 6 and 14) with the battery disconnected. A reading of 120 Ohms indicates one of the two terminating resistors (in the BCM and EBCM) is offline.. Failure: A reading significantly different from 60 Ohms (e.g., 0 Ohms, OL, or 120 Ohms) points to a wiring fault or module issue on the data bus.
• BCM Ground (G218) Integrity — expected: Less than 0.2 Ohms of resistance between the ground stud and the negative battery terminal. A loaded voltage drop test should show minimal voltage.. Failure: High resistance or voltage drop indicates a poor ground connection, often due to the dash insulator mat being trapped under the ground eyelet.

Scan Tool Commands That Help

• GDS2 (GM Dealer Scan Tool): EBCM Data List -> 'Brake Fluid Level Sensor' — To confirm the root cause identified in TSB PIT5490B. This allows you to see if the EBCM is reporting 'Low' fluid status, even if the reservoir appears full, which would point to a sensor or circuit issue rather than just low fluid.
• GDS2 / SPS (Service Programming System): Module Replacement and Programming — After replacing the EBCM or TBCM, the new module must be programmed with the vehicle's VIN and correct software configuration. This function downloads the latest calibration from GM's servers and installs it onto the new module to ensure it communicates correctly with other modules on the network.

Wiring & Ground Locations

• G218 — Behind the driver's side of the instrument panel, near the kick panel area. It is a ground stud on the body.. This is a primary ground for the Body Control Module (BCM). TSB PIT5405C identifies a poor connection here (often due to sound insulation getting trapped under the terminal) as a cause for numerous communication DTCs, including U0415, due to unstable BCM operation.
• Circuit 5986 (Communication Enable) — This wire runs from the BCM to multiple modules, including the EBCM. It is known to be damaged under the driver's and passenger's sill plates.. This circuit acts as a 'wake-up' signal for modules like the EBCM. If the signal is lost due to a broken wire (a known issue per TSB PIT5457D), the EBCM won't communicate on the CAN bus, leading to U0121 and U0415 codes.
• Splice J365 — Located in the wiring harness under the passenger front sill plate.. This is a splice point for Circuit 5986. Corrosion or a poor connection at this splice can cause the same loss of communication to the EBCM as a broken wire.
• EBCM Connector (X1) — The main 38-pin electrical connector at the Electronic Brake Control Module, located on the driver's side frame rail.. This is the primary connection point for all EBCM power, ground, and data signals. Specific pins are used for testing, such as the pin for Circuit 5986, to diagnose if the fault is in the wiring or the module itself.

Real Owner Repair Stories

• gm-trucks.com forum user (2015 GMC Sierra) — "Service Trailer Brake System", "Service Stabilitrak" messages, and code U0415.
  ❌ Tried (didn't work) Topping off brake fluid (level was not low)., Checking connections at the trailer brake control module.
  ✅ What actually fixed it The owner found corroded and broken wires in the harness located under the driver's side door sill plate, consistent with TSB PIT5457D. After repairing the broken wires, all messages and codes were resolved.

Model Year Variations Within This Range

• 2019: The 2019 model year marked the introduction of the new T1 platform for the 1500 series, while the 2500/3500 HD models remained on the K2XX platform for one more year (designated 'Sierra Limited'). However, both shared many electrical systems. The all-new 2019 Sierra 1500 introduced different interior technology options, like an available heads-up display and rear camera mirror, which were not on the 2015-2018 models, potentially adding complexity to network diagnostics. Despite these changes, the underlying causes for U0415 related to wiring (sill plates, grounds) and low brake fluid remained consistent across the 2015-2019 HD range.