U0028 on 2013-2017 GMC Sierra 3500: MOST Bus Communication Fault Guide

What's Unique About the 2013-2017 Gmc SIERRA 3500

Unlike the standard CAN bus networks that control the engine and chassis, GM uses the MOST bus protocol specifically for the high-bandwidth needs of the infotainment system. This network operates in a ring topology, meaning every module must be powered and communicating correctly to pass the signal to the next one in the loop. A single point of failure—be it a wire or a module—can bring down the entire system, which is a common experience for owners of these trucks, often due to the factory wiring harness pinch point documented in TSB PIT5288H.

Diagnostic Flowchart

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

Generation note: This year range covers the end of the GMT900 generation (through 2014 for HD models) and the start of the K2XX generation (2015-2019 for HD models). While both use a MOST bus architecture, the specific modules and their locations may differ slightly. However, the primary cause—a pinched dash harness—is a well-documented issue on the K2XX platform trucks (2015+) covered in this range, as detailed in TSB PIT5288H.

Symptoms You May Notice

• Blank radio or infotainment screen (display is completely black)
• No audio from the stereo system, but chimes may still work
• Inoperative steering wheel controls for audio
• Loss of navigation functions
• OnStar or telematics system not working
• Intermittent no-start condition
• Dead battery due to parasitic drain
• Radio controls are inoperative
• DIC (Driver Information Center) audio page is blank

Most Likely Causes

1. Pinched or Damaged Dash Wiring Harness 🔴 High Probability A known manufacturing flaw documented in GM TSB #PIT5288H describes the 🎬 See how to diagnose U0028 codes and blank displays main dash harness getting pinched and chafed by a sharp metal instrument panel mounting bracket. This bracket is located behind the driver's side dash, near the parking brake assembly. The pinching can crush or sever the twisted-pair MOST bus wires, causing an open or short circuit.
   How to confirm: Remove the driver's side lower dash/kick panel and the I/P fuse block cover. From underneath the dash, visually inspect the large wiring harness where it passes the left I/P mounting bracket. The TSB shows images of the pinch point. Check if the harness can move freely; if it's tight against the bracket, damage is likely even if not immediately visible.
   Typical fix: Loosen the I/P dash mounting bracket bolts to free the harness. Carefully cut open the harness conduit, inspect for broken or chafed wires (they are often a twisted pair), and perform a proper splice and solder repair. Insulate the repair well and reroute the harness to prevent it from being pinched again.
   Est. part cost: $10-$50 for wire repair supplies.
2. Failed Human Machine Interface (HMI) Module 🟡 Medium Probability The HMI module, located behind the glove box, is the central processor for the infotainment system. It is a complex electronic unit that is a common point of internal failure, which breaks the MOST communication ring. In some cases, this can be due to internal corrosion from moisture.
   How to confirm: After confirming the wiring is intact, use a MOST bus bypass loop (special tool EL-51578) on the HMI module's connector. If bypassing it restores function to the rest of the system (e.g., audio returns, though the screen will be blank), the HMI module is faulty.
   Typical fix: Replace the HMI module. The new module must be programmed to the vehicle's VIN. Some aftermarket vendors sell pre-programmed modules if you provide your VIN.
   Est. part cost: $250-$500
3. Failed Radio, CD Player, or Amplifier ⚪ Low Probability Because the MOST bus is a ring, any module in the loop can fail and break communication. The CD player, radio tuner, or amplifier can fail internally, stopping the signal from being passed to the next module. An iATN case study on a 2015 Silverado with U0028/U0029 identified a failed CD player as the culprit.
   How to confirm: Use a MOST bus bypass loop to systematically test each module in the ring. When the faulty module is bypassed, the system will come back online. For example, in one documented repair, jumping the data lines at the CD player connector restored all other functions, proving it had failed internally.
   Typical fix: Replace the failed module. In some cases, like a CD player, it can simply be bypassed and left disconnected if the feature is not needed.
   Est. part cost: $150-$600 depending on the module.
4. Poor Ground Connection (G218) ⚪ Low Probability TSB #PIT5405C notes that a poor ground at the G218 location (under the driver's side dash near the A-pillar) can cause various communication codes, including U0028. Sound deadening material can sometimes get trapped under the ground terminal from the factory, causing a weak connection and a host of intermittent electrical issues.
   How to confirm: Locate ground G218 under the driver's side dash. Remove the nut and ground eyelet, and thoroughly clean the terminal and the contact surface on the chassis to ensure a bare metal connection.
   Typical fix: Clean and secure the ground connection, ensuring no insulation is trapped underneath.
   Est. part cost: $0

Diagnosis Steps

1. Perform a full vehicle scan with a high-end scan tool (like GM's GDS2) to see which modules are reporting communication loss and if U0028 is current or history. Check for specific symptom bytes (e.g., sym00, 72) for additional clues.
2. Based on the high probability documented in TSB #PIT5288H, the first physical check should be the wiring harness. Remove the driver's side lower dash panel and inspect the harness near the left instrument panel bracket for pinching or damage, as detailed in the TSB.
3. If the harness is intact, check for poor grounds, specifically G218 under the driver's dash, for looseness or trapped insulation per TSB #PIT5405C.
4. If wiring and grounds are good, use a MOST bus bypass loop (GM tool EL-51578) to diagnose the ring. The typical ring order is 🎬 Watch: A deep dive into MOST bus circuitry and testing Radio -> CD Player -> HMI Module -> Instrument Panel Cluster -> Amplifier (if equipped) -> back to Radio.
5. Start by bypassing the most accessible module (e.g., the CD player or HMI module behind the glove box). Connect the loop to the module's harness connector.
6. If bypassing a module restores function (e.g., the screen turns on or audio returns) and the U0028 code changes to 'History', that module is the source of the fault.
7. A technician can also use scan tool data to help. For example, a 'Surrogate MOST Master Node Upstream Position' of 2 points to a fault at the CD player, which is the second module before the HMI in the ring.
8. If all modules are bypassed one by one and the fault persists, the issue is in the wiring between modules or an internal fault in the radio (the master module, which cannot be bypassed with the tool).
9. Check powers and grounds to the suspected faulty module before ordering a replacement part.

Parts You'll Likely Need

• Human Machine Interface (HMI) Module (OEM #23228496, 23443746 (Part numbers are frequently superseded; always verify with VIN)) — This is the central computer for the infotainment system and a common point of internal failure that will break the MOST bus ring. It requires VIN-specific programming upon replacement.
  Trusted brands: ACDelco
  OEM price range: $300-$500
  Aftermarket price range: $250-$400 (Often sold as remanufactured and pre-programmed)
• Radio/Tuner Module — The radio acts as the master of the MOST bus. If it fails internally, the entire network will go down. It cannot be bypassed for diagnosis.
  Trusted brands: ACDelco
  OEM price range: $400-$700
  Aftermarket price range: $300-$550
• MOST Bus Bypass Loop (OEM #EL-51578) — This is a required diagnostic tool to isolate which module on the MOST bus has failed. It is not a repair part but is essential for accurate diagnosis to avoid replacing good parts.
  Trusted brands: Kent-Moore (OEM), Various aftermarket kits
  OEM price range: $90-$150 (for the full kit)
  Aftermarket price range: $20-$40 (for individual loops)

Related Codes That Often Appear With This One

• U0029 — This is also a MOST bus communication code. U0028 often indicates a complete break in the ring, while U0029 can mean the ring has integrity but a module is not communicating correctly. They are frequently set together and are listed in the same TSBs.
• B127B — Mentioned in TSB #PIT5405A, this code can appear when infotainment communication issues cause the screen to go blank.
• U0151, U0126, U0415, etc. — A failure on the MOST bus, especially one caused by the pinched harness described in TSB #PIT5288H, can damage adjacent wires for other networks. This can cause a cascade of 'Loss of Communication' codes to be set in unrelated modules like the airbag (U0151) and Stabilitrak (U0126) systems.

Technical Service Bulletins (TSBs) & Recalls

• PIC6073E: Directs technicians to review Media Oriented Systems Transport (MOST) bus operation and use diagnostic tool EL-51578 when diagnosing U0028 and related symptoms like a blank display.
• PIT5288H: Documents a pinched dash harness at the left instrument panel bracket causing U0028/U0029 and a host of other electrical symptoms, including a dead battery or no-start. Provides images for locating the pinch point.
• PIT5405C: Notes that a poor ground at G218 can cause numerous intermittent electrical issues and communication DTCs, including U0028, especially when turning the steering wheel at low speeds.
• PI1149A: Provides diagnostic aid for intermittent blank displays with or without audio, specifically noting that if U0028 is stored, the root cause is a fault bringing the entire MOST bus down.

Platform-Specific Known Issues

• Pinched Dash Harness at I/P Bracket: A pinched wire harness at the left instrument panel bracket is a well-documented factory issue covered by TSB #PIT5288H, making it the most likely cause of U0028 on these trucks. The TSB includes diagrams showing the exact location near the parking brake assembly.
• iATN Case Study: Failed CD Player: A detailed diagnostic case on the International Automotive Technicians' Network (iATN) for a 2015 Silverado with U0028 and U0029 traced the fault to an internal failure of the CD player module. Bypassing the CD player restored all other infotainment functions, confirming it as the single point of failure.

Mechanic-Grade Diagnostic Values

• High-Speed GMLAN Bus Resistance — expected: Approximately 60 Ω. Failure: A reading of 120 Ω indicates an open in the bus or that one of the two terminating resistors is offline. This test is for the GMLAN bus, not the MOST bus, but is a common parallel diagnostic step as harness damage can affect both.

Hidden / Shadow Codes Worth Checking

• U0028 sym00: A general MOST bus communication fault. Its presence confirms the bus master (radio) is setting the code. (see via GM GDS2 (Global Diagnostic System 2) or equivalent high-end professional scan tool.)
• U0028 72: Symptom byte '72' means 'Alive and Well Counter Incorrect'. This indicates that data is being received, but it is corrupted or not in the expected format, pointing towards a module failing internally rather than a complete wire break. (see via GM GDS2 (Global Diagnostic System 2) or equivalent high-end professional scan tool.)
• U0029 7F: Symptom byte '7F' means 'Intermittent'. When seen with U0028, it strongly suggests a fault that is not continuously present, such as a chafed wire that makes intermittent contact or a loose connection. (see via GM GDS2 (Global Diagnostic System 2) or equivalent high-end professional scan tool.)

Scan Tool Commands That Help

• GDS2: Radio Data > MOST Data > 'Number of MOST Communication Breaks' — Use this to determine if there is a physical break in the MOST ring. A value of 1 or more indicates a complete break. If the value is 0 but U0028/U0029 is present, it suggests the ring is physically intact but a module is failing internally.
• GDS2: Radio Data > MOST Data > 'Surrogate MOST Master Node Upstream Position' — This is a critical diagnostic PID. If a number (e.g., '2') is displayed, it tells the technician the location of the fault. The number corresponds to the module position counting backward from the HMI in the ring (e.g., '2' often points to the CD Player). This can significantly speed up diagnosis by telling you where to start testing.

Wiring & Ground Locations

• MOST Bus Wiring — Throughout the infotainment system, connecting the Radio, HMI, CD Player, and IPC.. These are the data wires for the affected network. They are typically a twisted pair. Common colors reported are Green and Gray, or Gray and a White/Green stripe. Identifying these wires is necessary to perform a bypass test on a module.
• HMI Connector (K74-X1) — Behind the glove box, connected to the Human Machine Interface module.. This connector contains both MOST bus wires and GMLAN bus wires. If the HMI module is removed for service, the GMLAN circuit can be broken, causing a no-start condition. Jumping pins 11 to 13 and 12 to 14 on this connector completes the GMLAN circuit and allows the truck to start while the HMI is out.

Real Owner Repair Stories

• YouTube user 'noonespecial' (2015 Chevy Silverado) — Blank screen, but backup camera worked. Codes U0028 and U0029 were present.
  ❌ Tried (didn't work) Replacing the screen did not fix the issue.
  ✅ What actually fixed it The CD/disc player had failed, bringing down the MOST network. The user unplugged the CD player and bridged the green and gray MOST bus wires in the harness connector, bypassing the module. This restored radio and screen function, and the owner opted to leave the CD player permanently bypassed.
• iATN Case Study (documented by Clore Automotive) (2015 Silverado) — MyLink display was dark, radio and control buttons were non-functional. Codes U0028 (current in Radio) and U0029 (current in HMI) were set.
  ✅ What actually fixed it The technician used a GDS2 scan tool and noted the 'Surrogate MOST Master Node Upstream Position' was '2'. Knowing the ring order (Radio->CD->HMI->IPC), this pointed to the CD player. The tech could not establish communication with the CD player module, confirming it had failed internally. Replacing the CD player would be the fix.

OEM Part Supersession History

• 23228498, 23212442, 84028492, etc. → Multiple, latest available part for VIN — Revisions for bug fixes and hardware improvements.
  Heads up: HMI modules are frequently superseded. Matching an old part number is less important than ensuring the replacement is the correct version (e.g., HMI 2.0 vs 2.5) and is programmed to the vehicle's specific VIN and options. A new module will not work without VIN programming.

Model Year Variations Within This Range

• 2013-2015: These models typically use the HMI 2.0 module, which does not support factory Apple CarPlay or Android Auto.
• 2016-2017: These models use the HMI 2.5 module, which introduced support for Apple CarPlay and Android Auto. The modules are not directly interchangeable without specific upgrade procedures and programming.