U0028 on 2013-2017 Buick Verano: Infotainment Black Screen and MOST Bus Fault Guide

What's Unique About the 2013-2017 Buick VERANO

The Buick Verano of this generation, like many other GM vehicles on the Delta II platform, relies on a ring-based MOST network for all infotainment functions. Unlike a traditional copper wire bus where one module failing might not affect others, the MOST bus's ring topology means a single point of failure can take down the entire system. If one module fails—or even loses power—it breaks the loop, causing the common symptoms of a blank screen and no audio from what is often just one faulty component. TSB PI1149A explicitly notes that a blank display with no audio *at startup* is the classic sign of a MOST bus down condition.

Diagnostic Flowchart

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

Symptoms You May Notice

• Blank infotainment or radio display screen, especially on startup.
• No audio from the radio, CD player, or any other source.
• Infotainment system controls are unresponsive.
• Loss of warning chimes or turn signal sounds that play through the audio system.
• "Audio Off" message may appear on the instrument cluster display.
• System may work intermittently or freeze before failing completely.

Most Likely Causes

1. Failed Module on MOST Bus (CD Player, HMI, Radio, Amplifier) 🔴 High Probability Electronic modules can fail internally over time. On the Verano and its platform mates, the CD Player and the HMI (Human-Machine Interface) module are the most frequently identified culprits for breaking the MOST ring.
   How to confirm: Use a scan tool to see which modules are setting the U0028 code. A GM-capable scanner can show the 'Surrogate MOST Master Node Upstream Position'. An upstream position of '0' points to a fault with the first module after the radio (the CD player). Then, use a fiber-optic bypass loop (GM tool EL-51578 or equivalent) to systematically bypass each module in the ring. When the faulty module is bypassed, the other infotainment functions will be restored, confirming the bypassed module is the one that failed.
   Typical fix: Replace the identified faulty module. New HMI or radio modules will require programming to the vehicle's VIN, though some vendors sell pre-programmed HMI modules.
   Est. part cost: $100-$800
2. Loss of Power or Ground to a Module 🟡 Medium Probability A blown fuse or a corroded ground connection can prevent a module from powering on, which breaks the MOST ring just as if the module failed internally. This is a common issue on the platform mate Chevy Cruze.
   How to confirm: As a first step, check the fuses for the infotainment system in the interior fuse panel, often labeled 'RDO' (Radio), 'AMP' (Amplifier), or 'DSPLY' (Display). Sometimes simply pulling and reseating the fuses can restore function. If fuses are good, before replacing a module, use a multimeter to verify it is receiving 12V power and has a solid ground connection at its electrical connector.
   Typical fix: Replace the blown fuse or clean/repair the faulty ground connection. In some cases, a simple power cycle by removing the fuse for 5 minutes can reset a glitching module.
   Est. part cost: $1-$20
3. Damaged or Disconnected MOST Bus Wiring ⚪ Low Probability The twisted-pair MOST bus wires can be pinched, kinked, or broken during unrelated repairs, especially if interior trim panels near the center console, glove box, or trunk are removed and reinstalled improperly.
   How to confirm: Visually inspect the wiring connected to each module for any signs of physical damage. Unlike fiber-optic systems, you cannot see a red light. Diagnosis relies on using a bypass loop or checking for continuity with a multimeter if a specific section of the harness is suspected.
   Typical fix: Repair or replace the damaged section of the wiring harness.
   Est. part cost: $50-$300

Diagnosis Steps

1. Perform a full vehicle scan with a capable scan tool to confirm U0028 and note any other communication codes (e.g., U0029, U0184). If module-specific codes like U0184 are present, diagnose them first per GM guidelines.
2. Verify the symptoms. A blank screen and no audio specifically at vehicle startup is a classic sign of a MOST bus failure.
3. As a preliminary step, check the infotainment-related fuses in the interior fuse panel. Fuses labeled 'RDO' or 'Display' are primary candidates. Pulling the fuse for five minutes and re-inserting can sometimes reset a temporary glitch.
4. If fuses are okay, obtain a MOST bus bypass loop (such as GM tool EL-51578).
5. Access the modules on the MOST ring. The specific ring order on the Verano is: Radio -> CD Player -> HMI Module -> Instrument Cluster -> back to Radio.
6. Start with the most common culprit, the CD Player, located behind the center dash controls. With the ignition off, disconnect the MOST connector and install the bypass loop.
7. Turn the ignition on. If the screen and audio functions are restored, the CD player you just bypassed is faulty.
8. If the system is still inoperative, turn the ignition off, reconnect the CD player, and move the bypass loop to the next module in the ring (the HMI module, typically behind the glove box). Repeat the process until the faulty module is isolated.
9. Before replacing the condemned module, use a multimeter to check for proper 12V power and ground at its main electrical connector to rule out a simple power supply issue.

Parts You'll Likely Need

• CD Player / Media Player — The CD player is a very common failure point on the MOST ring in the Verano and similar GM vehicles, causing a U0028 code. It is often the first module in the ring after the radio.
  Trusted brands: ACDelco
  OEM price range: $200-$400
  Aftermarket price range: $100-$250 (used/remanufactured)
• Human Machine Interface (HMI) Module (OEM #Varies by VIN/RPO code (e.g., IO5, IO6)) — The HMI module is the 'brain' for the display and a primary node on the MOST bus. It is another common failure point that will cause a black screen and set U0028.
  Trusted brands: ACDelco
  OEM price range: $400-$700
  Aftermarket price range: $250-$500 (used or pre-programmed from specialty vendors)
• Radio / Head Unit — The radio acts as the master module for the MOST bus. An internal failure will take down the entire network. It cannot be bypassed with the standard loop tool.
  Trusted brands: ACDelco
  OEM price range: $400-$800
  Aftermarket price range: $250-$500 (used/remanufactured)
• Audio Amplifier — If the amplifier fails, it will break the MOST ring, causing a total loss of audio and screen function. On the Verano, it is typically located under the rear package shelf in the trunk.
  Trusted brands: ACDelco
  OEM price range: $300-$600
  Aftermarket price range: $150-$350 (used/remanufactured)
• MOST Bus Bypass Loop (OEM #EL-51578) — This is an essential diagnostic tool required to isolate which module on the MOST bus has failed. It is not a repair part.
  OEM price range: $15-$40
  Aftermarket price range: $10-$25

Related Codes That Often Appear With This One

• U0029 — This code often appears with U0028. While U0028 indicates a general break, U0029 can sometimes mean the ring has integrity but a module is malfunctioning internally, helping to confirm a module failure over 🎬 Watch: Diagnosing a U0029 MOST bus communication fault. a wiring break.
• U0184 — Loss of Communication with Radio. This code may be set in other modules when the radio, which acts as the MOST bus master, goes offline due to the U0028 fault. TSB PI1149A advises diagnosing these specific codes first.
• U0186 — Loss of Communication with Audio Amplifier. This code will likely be present if the amplifier is the specific module that has failed or if the entire MOST ring is down.

Technical Service Bulletins (TSBs) & Recalls

• PIC6073E: Mentions reviewing the Media Oriented Systems Transport (MOST) bus description and operation for diagnostic trouble code U0028.
• PI1149A: Provides detailed diagnostic steps, noting that a blank display and no audio *at startup* is the key indicator of a MOST bus failure. It confirms the use of the essential tool EL-51578 (bypass loop) and advises that if other module-specific communication DTCs (like U0184 or U0186) are set, they should be diagnosed before U0028.

Platform-Specific Known Issues

• Confirmed CD Player Failure: In a diagnostic video focusing specifically on a Buick Verano with code U0028 and a blank screen, a technician identified the CD player as the cause. After confirming power and ground were present at the CD player's connector, the technician used a bypass loop. Installing the loop in place of the CD player immediately restored radio and screen function, confirming the CD player had failed internally and was breaking the MOST ring.

Mechanic-Grade Diagnostic Values

• Surrogate MOST Master Node Upstream Position — expected: A non-zero number indicates which module has taken over as the temporary 'master' after a ring break. The number corresponds to a position in the ring.. Failure: A value of '2' on a system where the CD player is the second node points to the CD player as the likely source of the communication failure. A value of '0' can point to the first module after the radio.
• Number of MOST Communication Breaks — expected: A number greater than 0.. Failure: If this value is '0' while code U0029 is also present, it suggests the ring itself is physically intact but a module is failing to communicate properly (internal fault), rather than a physical wiring break.

Hidden / Shadow Codes Worth Checking

• U0028 sym00: The 'sym00' is a GM-specific symptom byte that specifies a general MOST bus communication fault. Its presence, viewed in the radio module data, confirms the radio (as the bus master) is the one logging the fault. (see via GM GDS2 (Global Diagnostic System 2) or an equivalent high-end professional scan tool.)

Scan Tool Commands That Help

• GDS2: Data Bus Diagnostic Tool — This function within the GDS2 software actively polls the various data buses (including MOST) to determine which modules are communicating and which are not. It provides a top-down view of network health and is a primary step in diagnosing a U0028.
• GDS2: Radio MOST Data Display — After confirming a U0028, viewing the MOST-specific data PIDs within the Radio module is the next step. This is where you find critical clues like 'Surrogate MOST Master Node Upstream Position' and 'Number of MOST Communication Breaks' to pinpoint the location of the fault without immediately disassembling the dash.

Wiring & Ground Locations

• G103 — Located at the left rear of the engine compartment on the cowl, above the brake booster.. This is a major ground point that serves the Radio, Instrument Panel Cluster (IPC), and Body Control Module (BCM). A poor connection here can cause a loss of power to the radio or IPC, breaking the MOST ring and setting a U0028.
• G302 — Located under the center console, at the rear, below the rear fuse block.. This ground point specifically serves the Radio Amplifier. If the vehicle is equipped with a premium audio system, a failure of this ground can take the amplifier offline, breaking the MOST ring.
• HMI Module Connector — Behind the glove box, connected to the Human Machine Interface module.. Before condemning an expensive HMI module, it is critical to verify 12V power and ground at this connector with a multimeter. A loss of either will cause the module to go offline and break the ring. The specific pin numbers for power and ground should be checked against the vehicle's service manual.

Real Owner Repair Stories

• iATN (International Automotive Technicians Network) Forum Post (2015 Chevrolet Silverado (shares MOST architecture with Verano)) — MyLink display was dark, radio would not play, all control buttons were non-functional.
  ❌ Tried (didn't work) Initially suspected HMI or Radio failure without direct testing.
  ✅ What actually fixed it The technician used a GDS2 scanner and found U0028 in the radio and U0029 in the HMI. Scan data showed 'Surrogate MOST Master Node Upstream Position' of 2. Knowing the ring order was Radio -> CD -> HMI -> IPC, this pointed to the CD player. The technician confirmed they could not communicate with the CD player. Jumping the data lines at the CD player connector restored all function. The final fix was replacing the failed CD player.

Model Year Variations Within This Range

• 2013-2017: The specific infotainment system is identified by a Regular Production Option (RPO) code, found on a label in the glove box. The Verano could be equipped with IO4 (base 4.2-inch screen), IO5 (8-inch screen without navigation), or IO6 (8-inch screen with navigation). While the U0028 fault can occur on any of these, knowing the RPO code is critical when sourcing a replacement HMI module, as they are programmed differently. An IO6 module will not work correctly in a vehicle originally equipped with an IO5 system without reprogramming.
• 2016+: Starting in 2016, GM introduced the HMI 2.5 generation module, which added support for Apple CarPlay and Android Auto. Earlier HMI 2.0 modules (2013-2015) did not have this capability. The modules are not directly interchangeable without specific upgrade kits and programming.