U0129 on 2019-2020 GMC Sierra 1500: Lost Communication With Brake Module Fixes

What's Unique About the 2019-2020 Gmc SIERRA 1500

For the 2019-2020 Sierra 1500 (and its T1 platform-mate, the Chevy Silverado), this code is frequently linked to software issues and specific wiring vulnerabilities. GM has issued Technical Service Bulletins (TSBs) mentioning that a combination of U-codes, including U0129, can be resolved by reprogramming the Engine Control Module (ECM) or the Brake System Control Module (BSCM). [Bulletin #N192267870] A recall was also issued for 2019 models for an EBCM software error that could disable ABS and ESC. These trucks are also highly susceptible to engine wiring harness chafing at several known locations, which can short CAN bus circuits and cause a flood of communication codes. [Bulletin #PIT5713A]

Diagnostic Flowchart

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

Symptoms You May Notice

• ABS warning light is on
• StabiliTrak / ESC warning light is on
• Service Brake System message on the dashboard
🎬 See this quick fix for brake system failure messages
• Check Engine Light (MIL) is on
• Gauges sweeping while driving [Bulletin #PIT5713A]
• Multiple other warning lights may appear simultaneously [Bulletin #PIT5713A]
• Transmission may not shift correctly
• Engine may stall, run rough, or enter reduced power mode.
• Remote start may be disabled.

Most Likely Causes

1. Engine Control Module (ECM) or Brake System Control Module (BSCM) Software Glitch 🔴 High Probability → Shop ABS Control Module GM issued TSB #N192267870 for 2019 models where low battery voltage could trigger multiple U-codes, including U0129, requiring an ECM reprogram. [Bulletin #N192267870] TSB PIT5735B also notes a separate issue where the BSCM stays awake, setting communication codes, which is fixed with a BSCM software update. A recall (N192281130) also required an EBCM reprogram.
   How to confirm: A GM dealer or a qualified shop with access to GM's programming software (Tis2Web/Techline Connect) can check the current software calibration of the ECM and BSCM and compare it against the latest available versions referenced in TSBs.
   Typical fix: Reprogramming the Engine Control Module (ECM) and/or the Electronic Brake Control Module (EBCM) to the latest software version. [Bulletin #N192267870]
   Est. part cost: $0-$250
2. Wiring Harness Chafing or Damage 🔴 High Probability TSB #21-NA-149 is a comprehensive bulletin detailing multiple locations where the engine harness can chafe, a known issue on the T1 truck platform. An omitted retaining clip during assembly allows the harness to rub against sharp edges. This can interrupt CAN bus communication, causing U0129 and other codes. [Bulletin #PIT5713A]
   How to confirm: Visually inspect the engine wiring harness, particularly at the three main chafe points identified in TSB 21-NA-149: the ECM/TCM bracket, the driver's side upper control arm, and the shock tower bolt. Other spots vary by engine but include the camshaft cover (2.7L) and near the generator (3.0L). This often requires removing the driver's side wheel and wheelhouse liner for access.
   Typical fix: Repairing the damaged wires using approved methods (solder and heat shrink) and securing 🎬 Watch: Professional tips for repairing a damaged wiring harness the harness away from sharp edges. GM specifies using anti-abrasion tape or a dedicated Kevlar sleeve (P/N 84820678 or 84826758) and zip ties to prevent recurrence.
   Est. part cost: $15-$75
3. Poor Ground Connection 🟡 Medium Probability Modern trucks have numerous ground points critical for module communication. Corrosion or loose connections are common sources of intermittent electronic issues. TSB PIT5689A specifically identifies a loose or broken engine-to-body ground strap (G132/G134) 🎬 Watch: How to find and fix common GM ground issues on 2019-2020 models that can cause a no-start and various communication codes. Forum users often point to checking grounds as a key step for resolving widespread electrical faults.
   How to confirm: Locate and inspect the main ground points, especially the engine-to-body ground strap near the firewall. Disassemble, clean all contact surfaces to bright metal, apply dielectric grease, and re-secure them. A voltage drop test on the ground side of the BSCM connector can also confirm a bad ground.
   Typical fix: Cleaning and tightening the ground connections. In some cases, a new ground strap or cable end may be needed.
   Est. part cost: $1-$20
4. Failed Electronic Brake Control Module (EBCM/BSCM) ⚪ Low Probability → Shop ABS Control Module While less common than software or wiring faults, internal failure of the module can occur due to heat, moisture, or component defects. This should only be suspected after all other causes are ruled out.
   How to confirm: After verifying good power, ground, and CAN bus wiring to the module with a multimeter, a bidirectional scan tool that still fails to communicate with the EBCM points to an internal module failure.
   Typical fix: Replacing the Electronic Brake Control Module. The new module will require programming to the vehicle's VIN using dealer software.
   Est. part cost: $250-$500

Rare But Worth Checking

• Blown Fuse: Always a simple first check. The EBCM is powered by several fuses in the underhood fuse block. A blown fuse will cut all power and communication, causing the module to go offline.
• Low Battery Voltage: → Shop Vehicle Battery A weak or failing battery can cause unpredictable behavior in various control modules, leading to a flood of communication codes, including U0129. TSB N192267870 directly links this scenario to a required ECM update. [Bulletin #N192267870] Many owners report a host of electrical issues that are resolved by replacing an aging battery.
• Unseated TCM Connector: TSB 19-NA-228 describes a condition where the Transmission Control Module (TCM) connector is not fully latched, causing poor connections and a variety of communication DTCs. While not directly U0129, it highlights the sensitivity of the network to connector issues.

Diagnosis Steps

1. Connect a professional-grade OBD-II scanner capable of reading all vehicle modules, not just the ECM.
2. Check for any other DTCs. A long list of U-codes suggests a network-wide problem (wiring, ground, power) rather than a single faulty module. [Bulletin #PIT5713A]
3. Check for any applicable TSBs or Recalls with the vehicle's VIN. TSBs N192267870, 21-NA-149, and PIT5735B are highly relevant. [Bulletin #N192267870]
4. Inspect the battery and charging system. Ensure battery voltage is above 12.4V with the engine off and that the alternator is charging correctly (typically 13.5-14.5V) with the engine running. Low voltage can trigger communication faults. [Bulletin #N192267870]
5. Inspect all fuses related to the EBCM/ABS in the underhood fuse block.
6. Inspect and clean the main engine and chassis ground connections, paying close attention to the engine-to-body ground strap identified in TSB PIT5689A.
7. Thoroughly inspect the engine wiring harness for chafing. Remove the driver's side front wheel and wheelhouse liner to access the key areas detailed in TSB #21-NA-149: the ECM/TCM bracket, upper control arm, and shock tower bolt.
8. If wiring and power/grounds are good, consult a dealer or qualified shop to check if an ECM or BSCM software update is available and perform the reprogram as per TSBs N192267870 or PIT5735B. [Bulletin #N192267870]
9. If all of the above checks out, the final step is to test the power, ground, and CAN bus signals directly at the EBCM connector. If signals are present but the module won't communicate, the EBCM has likely failed and needs replacement and programming.

Parts You'll Likely Need

• Electronic Brake Control Module (EBCM) (OEM #84634366) — This is the part to replace if it has been confirmed to have failed internally after ruling out all software, wiring, and power/ground issues. This part number supersedes 84074958 and requires programming upon installation.
  Trusted brands: ACDelco (GM Genuine)
  OEM price range: $250-$500
  Aftermarket price range: $250-$400
• Engine Harness Repair Materials (OEM #84820678 (Kevlar Sleeve)) — If the cause is harness chafing per TSB 21-NA-149, you will need materials to repair wires and protect the harness. GM specifies a particular Kevlar sleeve for this repair.
  Trusted brands: GM Genuine, Tesa Tape, Standard wire repair supplies
  OEM price range: $20-$50
  Aftermarket price range: $10-$30

Related Codes That Often Appear With This One

• U0100 — Lost Communication with ECM/PCM. Often appears with other U-codes when there is a general network problem, such as a chafed harness or bad ground. [Bulletin #PIT5713A]
• U0101 — Lost Communication with TCM. Like U0100, it points to a broader network or power/ground issue. It is specifically mentioned in TSB N192267870 along with U0129. [Bulletin #N192267870]
• U0140 — Lost Communication with Body Control Module. Its presence reinforces the likelihood of a systemic network, power, or ground fault rather than a single module failure. It is also listed in TSB N192267870. [Bulletin #N192267870]
• U0073 — Control Module Communication Bus 'A' Off. This is a general code indicating the entire high-speed CAN bus is down, often due to a wiring short or a failed terminating resistor, consistent with the chafing issue in TSB 21-NA-149. [Bulletin #PIT5713A]
• P25A2 — Brake System Control Module Requested MIL Illumination. This code is set by the ECM when the BSCM detects a fault and requests the Check Engine Light to be turned on. It is a pointer code that confirms the issue originates in the brake control system.

Technical Service Bulletins (TSBs) & Recalls

• N192267870: Addresses multiple U-codes, including U0129, being stored in the ECM and recommends an ECM reprogram.
• PIT5713A (superseded by 21-NA-149): Mentions U0129 as part of a large group of DTCs caused by network issues, manifesting as sweeping gauges and multiple warnings.
• 21-NA-149: Details common locations for engine wire harness chafing that can cause communication codes.

Platform-Specific Known Issues

• A recall (NHTSA Campaign ID: 19V889000, GM #N192281130) was issued for 2019 Sierra 1500s due to an EBCM software error that could disable ABS and ESC without warning. The fix is a software reprogram.
• TSB #N192267870 addresses a condition on 2019 models where multiple U-codes, including U0129, are stored after a low-voltage event, and the fix is to reprogram the ECM.
• TSB #21-NA-149 (superseding PIT5713A) points to widespread issues with engine harness chafing on 2019-2022 models, causing a variety of electrical faults and communication DTCs. Key inspection points are the ECM bracket, upper control arm, and shock tower.
• TSB #PIT5735B describes a specific software issue where the BSCM stays awake after shutdown, causing communication DTCs. The fix is a BSCM software update.

Mechanic-Grade Diagnostic Values

• High-Speed CAN Bus Resistance at DLC — expected: Approximately 60 Ohms. Failure: A reading of 120 Ohms indicates an open circuit or that one of the two terminating resistors is offline. A reading significantly lower than 60 Ohms indicates a short between the CAN High and CAN Low wires.
• CAN High (Pin 6 at DLC) to Ground (Pin 4 or 5) Voltage — expected: Approximately 2.5V (Key On, Engine Off). Failure: Voltage significantly higher or lower than 2.5V can indicate a short to power or ground on the CAN High line.
• CAN Low (Pin 14 at DLC) to Ground (Pin 4 or 5) Voltage — expected: Approximately 2.5V (Key On, Engine Off). Failure: Voltage significantly higher or lower than 2.5V can indicate a short to power or ground on the CAN Low line.

Hidden / Shadow Codes Worth Checking

• U-code with Symptom Byte 71: Indicates that a module received invalid data from another module. For U0129, this means another module (like the ECM) received an invalid signal from the Brake System Control Module. This points away from the receiving module and toward the sending module (BSCM) or its inputs (like a wheel speed sensor). You should not replace the module reporting the byte 71 code. (see via GM's GDS2/Tech2 dealer scan tool or an advanced aftermarket scanner that can read manufacturer-specific symptom bytes.)

Scan Tool Commands That Help

• GDS2 (Global Diagnostic System 2): Module Diagnostics > EBCM > Control Functions — To perform bidirectional tests on components controlled by the EBCM, such as individual solenoids or the ABS pump motor. This helps verify if the module is capable of commanding outputs, which confirms it is powered up and partially functional even if it has communication issues.
• GDS2 (Global Diagnostic System 2): Vehicle DTC Information > Clear All DTCs — Used after a repair (like fixing a ground or chafed wire) to clear codes from all modules simultaneously. Some communication codes may not clear from a single module's menu and require a global reset.
• GDS2 (Global Diagnostic System 2): Module Replacement and Setup > EBCM — This function is mandatory after replacing the Electronic Brake Control Module. It involves programming the module with the correct software and then performing a setup procedure to configure it to the vehicle's specific options. Failure to perform the setup will result in a C056E code and the ABS/ESC system will remain inoperative.

Wiring & Ground Locations

• G131 / G132 / G134 — The main body-to-frame ground strap. On the passenger side, it runs from the firewall down to the frame, near the front body support.. This is a critical ground path for multiple modules. TSB PIT5689A specifically identifies this strap becoming loose or corroded, causing widespread communication codes, including U0129. It is a very common failure point due to its exposure to the elements.
• EBCM/BSCM Connector (K17) — The main electrical connector at the Electronic Brake Control Module, which is attached to the ABS hydraulic block in the engine compartment.. This is the primary connection point for all power, ground, and CAN bus signals to the brake module. Technicians test for voltage, ground integrity, and CAN bus signals at the pins of this connector to determine if the fault is in the wiring to the module or the module itself.
• Engine Block to Chassis Ground — A braided strap typically located on the rear of the engine block (often near a sensor) connecting to the firewall/chassis.. A poor connection at this point can cause electrical noise and voltage fluctuations that disrupt module communication. A user-submitted video showed that replacing a burnt strap at this location resolved numerous electrical glitches and warning lights.

Real Owner Repair Stories

• Reddit user J_Schnetz (2020 Silverado (platform mate)) — A flood of ~50 check engine light codes, loss of power steering, trailer brake errors, loss of ABS, loss of traction control. The truck was described as a 'mental patient off its medication'.
  ❌ Tried (didn't work) Replacing the battery, Having the alternator checked
  ✅ What actually fixed it The braided body-to-frame ground strap was found to be severely corroded. Replacing this single ground strap resolved all the codes and symptoms. Another user noted this is a known issue and the strap is located on the passenger side, accessible by removing the front wheel liner.
• YouTube video comment by a Bosch engineer (2019+ GM Truck) — After a brake pad change, the truck enters limp mode with multiple brake warnings and a mushy pedal. The computer thinks there is a loss of pressure because the pedal went to the floor during the service.
  ❌ Tried (didn't work) Cycling the ignition and driving around, which only sometimes worked., Clearing codes with a standard scanner before performing a relearn.
  ✅ What actually fixed it A specific relearn procedure was required: 1. With the engine off, press and hold the start button (without pressing the brake) until the truck enters accessory mode. 2. Firmly press and HOLD the brake pedal to the floor for ~5 minutes to allow the computer to relearn that there are no pressure leaks. 3. After this, use a scan tool to delete all codes. The codes would not clear prior to performing this pedal-hold relearn procedure.

OEM Part Supersession History

• Varies by specific vehicle options → 84662980 (example for 2020-2022 models without auto-brake) — Part revisions for reliability or feature updates.
  Heads up: The EBCM is highly specific to the vehicle's VIN and options (e.g., with/without auto-brake). The correct part number must be ordered by VIN. All replacements require programming and a special setup procedure using GM's GDS2 software to function.

Model Year Variations Within This Range

• 2020: The 2020 models introduced available adaptive cruise control, which uses the brake control module. While not a direct cause of U0129, it adds complexity to the EBCM's function and software compared to the 2019 model which did not offer this feature.
• 2020+: Starting in 2020, GM began isolating the Data Link Connector (DLC) from the main high-speed CAN bus via the Serial Data Gateway Module (SDGM). On a 2019, measuring resistance across pins 6 and 14 at the DLC checks the entire network (should be ~60 ohms). On a 2020, this same test only checks the resistance of the SDGM itself (should be ~120 ohms), which can be misleading if a technician is unaware of the change.