U0029 on 2014-2019 GMC Sierra 1500: Communication Bus Fault Causes and Fixes

What's Unique About the 2014-2019 Gmc SIERRA 1500

The K2XX generation of the GMC Sierra (2014-2019) and its platform mates are known for a specific wiring vulnerability. General Motors issued a Technical Service Bulletin (#PIT5288H) that identifies a common cause for U0029 and other communication codes: a main wiring harness getting pinched between the left I/P dash mounting bracket and the body. This can happen during assembly or over time and can be difficult to see without pulling the harness away from the bracket. This specific, documented issue makes it a primary suspect, unlike in other vehicles where the cause might be more generic.

Diagnostic Flowchart

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

Symptoms You May Notice

• Radio, infotainment screen, or touchscreen is blank or inoperative.
• No audio from the stereo system, no chimes. [Bulletin #PIT5586G, 10]
• HVAC controls are inoperative. [Bulletin #PIT5586G]
• Instrument panel cluster goes blank or flickers. [Bulletin #PIT5405B, 1]
• Steering wheel controls do not work. [10, Bulletin #PIT5405C]
• Dead battery due to modules not shutting down correctly. [10, Bulletin #PIT5288H]
• Wipers continue to run for a short time after turning the vehicle off. [Bulletin #PIT5405C]
• "Service Stabilitrak" message appears on the DIC.
• Backup camera works, but nothing else on the screen does.

Most Likely Causes

1. Pinched Wire Harness Behind Instrument Panel 🔴 High Probability A known issue documented by GM in TSB #PIT5288H. The dash harness can be pinched between the left I/P dash mounting bracket and the body during assembly or over time. The bulletin notes this can be an upper or lower pinch point near the parking brake pedal assembly.
   How to confirm: Visually inspect the wiring harness located on the left side of the instrument panel, near the dash mounting bracket and parking brake pedal. You may need to remove the driver's side knee bolster and side dash panel for access. Check if the harness is caught, pinched, or unable to move freely. The damage may not be obvious without manipulating the harness.
   Typical fix: Loosen the I/P dash mounting bracket bolts, free the harness, inspect for damaged wires, and repair any chafed or broken wires with appropriate splicing techniques and heat shrink. Reroute the harness to prevent future pinching.
   Est. part cost: $5-$25 for wire, tape, and connectors.
2. Failed Module on the MOST Bus 🟡 Medium Probability The MOST bus operates in a ring. If one module fails (e.g., Radio, CD Player/Media Disc Player, HMI module), it can break the entire communication ring. The CD player is a very common point of failure and is often bypassed rather than replaced.
   How to confirm: A professional scan tool can show which modules are not communicating. A common DIY method is to use a MOST bus bypass loop (a special fiber-optic or electrical jumper, GM tool EL-51578) to bypass one module at a time. Unplug a module (like the CD player), install the loop, and if communication is restored to other modules, the bypassed module is faulty.
   Typical fix: Replace the failed module or, in the case of the CD player, permanently install the bypass loop. The HMI and Radio modules require programming after replacement.
   Est. part cost: $150-$800 depending on the module.
3. Poor Ground Connection at G218 🟡 Medium Probability These trucks are known for having a poor ground connection at location G218, which is located under the dash on the driver's side, near the A-pillar and speaker. Factory sound-deadening material can get trapped under the ground lug, causing a high-resistance connection that leads to flickering lights and various communication codes.
   How to confirm: Access the G218 ground stud by removing the driver's side A-pillar trim and dash side panel. Inspect the connection for corrosion or trapped material. Many owners report seemingly random electrical issues that are resolved by cleaning this ground.
   Typical fix: Remove the nut, clean the contact surfaces of the ground lug and the chassis with a wire brush or sandpaper, and re-secure the connection tightly. Some owners add a star washer to ensure a better bite.
   Est. part cost: $0-$5 for cleaning supplies.

Rare But Worth Checking

• Corroded Connectors: Water intrusion, especially from a leaking windshield or A-pillar, can corrode connectors for network modules, causing intermittent communication failures.
• Failed Serial Data Gateway Module (SDGM): A less common but possible cause is an internal error in the SDGM, which can cause it to stop communicating on CAN channels. This may require reprogramming or replacement of the SDGM.

Diagnosis Steps

1. Check Battery and Charging System: Ensure the battery voltage is stable and above 12.4V. Low or fluctuating voltage can cause numerous communication errors.
2. Scan for All Codes: Use a high-quality OBD-II scanner that can read manufacturer-specific codes (B-codes, C-codes, U-codes) from all modules. Note all present codes and which modules are not communicating.
3. Inspect the Pinched Harness Area (TSB #PIT5288H): This is the most likely cause. Remove the driver's side dash end cap and knee bolster to gain access to the left side of the instrument panel. Locate the main dash harness near the metal mounting bracket and check thoroughly to see if it is being pinched or has been damaged. The pinch point can be high or low on the bracket.
4. Repair Harness if Damaged: If you find a pinched or damaged harness, disconnect the battery. Carefully repair any broken or chafed wires using solder and heat shrink or approved connectors. Reroute the harness to prevent it from being pinched again.
5. Inspect Ground G218: If the harness is OK, inspect the G218 ground connection. It's located behind the driver's side A-pillar trim, near the speaker. Remove the nut, clean all contact surfaces to bare metal, and re-tighten securely.
6. Check MOST Bus Integrity: If wiring and grounds are good, the problem is likely on the MOST bus ring. The modules in the ring typically include the Radio, CD/Media Player, HMI Module, and Instrument Cluster.
7. Use a Bypass Loop: The most effective way to find a failed module on the ring is to use a MOST bypass loop (GM Tool EL-51578). Unplug a module and install the loop in its place. If the other modules start working, you have found the faulty component. Start with the CD player, as it is a very common failure point.
8. Inspect Module Connectors: If you don't have a bypass loop, visually inspect the connectors at each module for corrosion, bent pins, or loose connections.
9. Clear Codes and Test: After any repair, clear all DTCs and perform a full ignition cycle to see if the codes return.

Parts You'll Likely Need

• Wiring Repair Supplies — To fix the common issue of a pinched or chafed wiring harness as described in TSB #PIT5288H.
  Trusted brands: 3M
  Aftermarket price range: $5-$25
• Human Machine Interface (HMI) Module (OEM #23443745 (2014 models), 84331775 (2018-2019 models). Part numbers vary by year and options.) — If the HMI module fails, it can bring down the entire MOST communication bus, causing code U0029. This module controls the infotainment screen and requires programming.
  Trusted brands: ACDelco
  OEM price range: $400-$700
  Aftermarket price range: $250-$500
• Media Disc Player (CD Player) — The CD player is a very common point of failure on the MOST bus. Its failure will break the communication ring. Many owners choose to bypass it rather than replace it.
  Trusted brands: ACDelco
  OEM price range: $200-$400
  Aftermarket price range: $100-$250
• MOST Bus Bypass Loop (OEM #EL-51578) — Essential diagnostic tool for isolating a failed module on the MOST ring network.
  Trusted brands: GM Essential Tools
  OEM price range: $50-$100
  Aftermarket price range: $20-$40

Related Codes That Often Appear With This One

• U0028 — U0028 is also a Vehicle Communication Bus A code. They often appear together when there is a MOST bus fault.
• U0140 — Lost Communication With Body Control Module. This can be a symptom of the main bus failure that also causes U0029. [Bulletin #PIT5405B]
• U0155 — Lost Communication With Instrument Panel Cluster (IPC) Control Module. The IPC is on the network, and if the bus is down, this code will set. [Bulletin #PIT5586G]
• U0184 — Lost Communication With Radio. The radio is a key module on the MOST bus, and this code is common when the ring is broken. [Bulletin #PIT5586G]

Technical Service Bulletins (TSBs) & Recalls

• PIT5288H: Dead battery and various DTCs including U0029 due to a pinched wire harness at the left instrument panel.
• PIT5586G: Multiple communication DTCs including U0029 causing inoperative HVAC controls.
• PIT5405B / PIT5405C: Instrument cluster/HVAC going blank with multiple DTCs including U0029.
• PI1149A: Diagnostic aid for infotainment system issues, including MOST bus faults like U0028 and U0029.

Platform-Specific Known Issues

• TSB #PIT5288H: Explicitly calls out a pinched wire harness behind the left side of the instrument panel as a cause for U0029 and other communication codes, leading to symptoms like a dead battery, blank screen, and no audio.
• TSB #PIT5405B / #PIT5405C: Note that U0029 can be set along with a host of other communication codes when the instrument panel or other modules go blank.
• Grounding Issue G218: A well-documented issue on forums where a poor ground connection under the driver's side dash causes widespread, intermittent electrical problems that can mimic module failure.

Mechanic-Grade Diagnostic Values

• High-Speed GMLAN Bus Resistance — expected: 60 ohms +/- 5 ohms. Failure: A reading of 120 ohms indicates an open in the bus or one of the two termination resistors has failed. A reading less than 60 ohms indicates the bus wires are shorted together.
• GMLAN Bus Voltage — expected: Approximately 2.5V on each leg (High and Low) at rest. During communication, the High leg toggles up to 3.5V and the Low leg toggles down to 1.5V.. Failure: Voltage significantly deviating from 2.5V at rest, or signals that do not show the proper toggle, can indicate a short, open, or module failure.

Hidden / Shadow Codes Worth Checking

• U0028 / U0029 with GDS2 Data: While not hidden codes, a GM dealer scanner (GDS2) provides critical context. The parameter 'Surrogate MOST Master Node Upstream Position' helps pinpoint the location of a communication break. A value of '0' often means the radio (master) cannot talk to the first module in the ring (often the CD player). A value of '2' points to a break before the third module in the ring. U0029 specifically indicates a performance error where the ring still has integrity, distinguishing it from U0028 which can mean a complete ring break. (see via GM GDS2 (Global Diagnostic System 2) software)

Scan Tool Commands That Help

• GDS2: Radio Data Display -> MOST Communication Data — This screen is critical for diagnosing U0029. It shows the 'Number of MOST Communication Breaks' and 'Surrogate MOST Master Node Upstream Position', which are key indicators for locating the fault in the MOST ring without physically disconnecting parts.
• GDS2: Module Programming (SPS) — Required after replacing the HMI module or Radio. The new module must be programmed with the vehicle's VIN and specific configuration using the Service Programming System (SPS) to function correctly.

Wiring & Ground Locations

• HMI Module — Located behind the glove box on the passenger side of the vehicle.. The HMI module is a key node on the MOST bus. A failure of this module or its connectors will break the communication ring and set codes U0029 and U0028.
• Pinched Harness (TSB PIT5288H) — The main dash harness can be pinched between the left I/P (Instrument Panel) dash mounting bracket and the body, near the parking brake pedal assembly.. This is a documented, high-probability cause for U0029. The pinch can damage wires for the communication bus, leading to intermittent or total failure of the infotainment system.
• GMLAN Termination Resistors — The high-speed GMLAN bus has two 120-ohm termination resistors. One is typically internal to the ECM. The other is often at the opposite end of the bus, sometimes as a standalone resistor taped into the harness or inside another module.. A failure of one of these resistors will change the total bus resistance from 60 ohms to 120 ohms, causing signal integrity issues and setting performance codes like U0029.

Real Owner Repair Stories

• YouTube video by 'Repairs and Rides' (2015 Chevrolet Silverado) — Blank infotainment screen, but the backup camera still worked. Codes U0028 and U0029 were present.
  ❌ Tried (didn't work) The owner had already replaced the screen itself, which did not solve the problem.
  ✅ What actually fixed it The technician identified the CD/disc player as a likely cause. He removed the CD player and used a jumper on the MOST bus connector (gray and green wires) to bypass it. This restored network communication, and the radio and screen began working correctly. The final fix was to permanently eliminate the CD player by bridging the network connection.
• iATN Technical Discussion Forum (2015 Chevrolet Silverado) — MyLink display was dark, radio would not play, and all control buttons were non-functional. Codes U0028 (in radio) and U0029 (in HMI) were current.
  ✅ What actually fixed it Using GDS2 scan data, the technician noted the 'Surrogate MOST Master Node Upstream Position' was 2. On this 4-node system (Radio, CD, HMI, IPC), counting back two positions from the end of the line pointed to the CD player as the source of the fault. The technician could not communicate with the CD player. He removed the CD player and jumped the data lines in the connector, which immediately restored all infotainment functions. The cause was an internal failure of the CD player.

OEM Part Supersession History

• 23443745 → Multiple part numbers, including 23228498. — Part revisions and updates by the manufacturer.
  Heads up: This is an HMI 2.0 module for vehicles with RPO code IO4/IO5 (non-navigation). It is not directly compatible with 2016+ trucks which use HMI 2.5 hardware for Apple CarPlay/Android Auto.
• 84331775 → 84546902 — Part revisions and updates by the manufacturer.
  Heads up: This is an HMI 2.5 module for vehicles with RPO code IO5 (non-navigation). It is not backward compatible with 2014-2015 models without also changing the radio module and other components.

Model Year Variations Within This Range

• 2014-2015: These models use the HMI 2.0 generation of infotainment modules. They do not support Apple CarPlay or Android Auto. A common HMI part number is 23443745.
• 2016-2019: These models use the HMI 2.5 generation, which introduced support for Apple CarPlay and Android Auto. The hardware is different and not directly interchangeable with earlier years without additional parts and programming. A common HMI part number is 84331775.