U0028 on 2013-2018 Chevrolet Volt: Infotainment Network Failure Causes and Fixes

What's Unique About the 2013-2018 Chevrolet VOLT

The Chevy Volt, across both its first (2011-2015) and second (2016-2019) generations, relies heavily on the MOST network for all functions of its central touchscreen, which also displays critical vehicle information. Unlike some other GM vehicles like the Silverado where a pinched wire is a common cause, on the Volt, U0028 is more frequently traced to an internal failure of one of the modules on the network ring. A Reddit user with a 2017 Volt reported a persistent U0028 code that was ultimately resolved by replacing the HMI module after trying to swap the display screen first. Diagnosing this requires a specific process of elimination using a fiber-optic bypass loop to find the break in the chain.

Diagnostic Flowchart

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

Generation note: This range covers the first generation (2013-2015) and the second generation (2016-2018) of the Chevrolet Volt. While the infotainment systems (MyLink) and specific module part numbers differ between generations, the underlying MOST bus architecture and the U0028 fault code's meaning are consistent. The diagnostic approach using a bypass loop is the same for both. Gen 2 (2016+) HMI modules have different part numbers and capabilities (like Apple CarPlay) than Gen 1.

Symptoms You May Notice

• Completely blank or black center infotainment screen
• No audio from the radio, chimes, or turn signal clicks
• Radio and steering wheel controls are unresponsive
• Inability to use navigation or hands-free phone features
• Parasitic 12V battery drain, leading to a dead battery
• Loss of backup camera display
• USB ports are dead or do not charge/connect

Most Likely Causes

1. Failed Human Machine Interface (HMI) Module 🔴 High Probability The HMI module is the central computer for the infotainment system and is a widely reported failure point on this generation of GM vehicles, including the Volt. Multiple owners on forums like Reddit have confirmed this was the cause of their U0028 code and black screen.
   How to confirm: Use a MOST bus bypass loop (such as from GM kit EL-51578) to bypass the HMI module. The HMI module is typically located behind the glove box. If the other infotainment functions (like audio) return when the HMI is bypassed, the module is faulty.
   Typical fix: Replace the HMI module. The new module must be programmed to the vehicle's VIN by a dealership or a properly equipped independent shop. Some aftermarket vendors sell pre-programmed units.
   Est. part cost: $150-$400 for a used or remanufactured unit, $500-$800 for a new OEM part.
2. Failed Radio/Tuner Module 🟡 Medium Probability The radio module acts as the 'master' for the MOST bus, controlling the communication ring. An internal failure within this module will break the entire communication loop.
   How to confirm: The radio is the one module that cannot be bypassed with a standard loop tool because it is the bus master. If all other modules on the ring (HMI, amplifier, CD player) are tested with a bypass loop and the system still does not work, the radio module is the most likely culprit by process of elimination.
   Typical fix: Replace the radio/tuner module and have it professionally programmed to the vehicle's VIN.
   Est. part cost: $100-$300 for a used unit, $400+ for new.
3. Failed CD/Media Player or Amplifier ⚪ Low Probability Like the HMI, the CD player and amplifier (on models with premium audio) are nodes in the MOST ring. An internal electronic failure in either one will cause a U0028 code. A case study on the International Automotive Technicians Network (iATN) confirmed a failed CD player as the sole cause of a U0028 code.
   How to confirm: Use a MOST bus bypass loop to individually bypass the CD player and the amplifier. If bypassing one of these components restores function to the rest of the system (e.g., audio returns), that component has failed.
   Typical fix: Replace the faulty module or permanently bypass it with a loop if the function (e.g., CD player) is not needed. Programming is not typically required for these components.
   Est. part cost: $50-$200

Rare But Worth Checking

• Damaged Fiber-Optic Cable or Connector: While less common than module failure on the Volt, physical damage to the fiber-optic wiring or a loose/unseated connector at the back of a module can break the ring and cause a U0028 code. A visual inspection of the bright orange fiber-optic cables connected to each module is warranted during diagnosis.

Diagnosis Steps

1. Perform a full vehicle scan with a high-quality OBD-II scanner (like a GM MDI 2) to confirm U0028 is the primary code and to see which other 'U' codes are present.
2. Check for obvious symptoms: Is the center screen black? Is there no sound from the speakers? Does the backup camera work?
3. TSB PI1149A notes a key difference: if the fault exists at startup, the screen will be blank with no audio. If it occurs while driving, the clock may disappear but the screen might stay on.
4. Gain access to the modules on the MOST bus. In the Volt, this typically includes the HMI module (behind the glove box), the radio/tuner (in the center stack), and the amplifier (if equipped).
5. Acquire a MOST bus bypass loop (GM tool EL-51578 or equivalent).
6. Systematically unplug one module at a time and install the bypass loop in its place on the harness connector. This completes the fiber-optic ring without that specific module.
7. Start with an easily accessible module like the HMI or CD player. After bypassing a module, cycle the ignition and see if system functionality returns (e.g., audio starts playing, screen shows something).
8. If bypassing a specific module (e.g., the HMI) restores the system, that module is the source of the fault.
9. If all accessible modules are bypassed and the fault persists, the issue likely lies with the radio/tuner module, which is the bus master and cannot be bypassed with the loop.
10. Visually inspect the fiber-optic cables (typically orange) and connectors for any signs of damage, pinching, or loose connections.

Parts You'll Likely Need

• Human Machine Interface (HMI) Module (OEM #84089011 (2016-2017), 84546904 (2017-2018)) — This is the most common module to fail internally, breaking the MOST communication ring and causing the U0028 code. Multiple owners have confirmed replacement fixed the issue.
  Trusted brands: ACDelco
  OEM price range: $500-$800
  Aftermarket price range: $150-$400 (Used/Remanufactured)
• MOST Bus Bypass Loop (OEM #EL-51578 (Kit) or equivalent single loop) — This is an essential diagnostic tool, not a repair part. It allows you to temporarily complete the fiber-optic ring while bypassing a suspected faulty module to confirm the diagnosis.
  OEM price range: $20-$40
  Aftermarket price range: $10-$25

Related Codes That Often Appear With This One

• U0029 — This code for 'Vehicle Communication Bus A Performance' often appears with U0028. While U0028 can indicate a complete break in the ring, U0029 can indicate an intermittent issue or a problem where the ring has integrity but a module is not communicating correctly.
• U0184 — This code means 'Lost Communication With Radio'. It is a secondary code that gets stored in other modules when the primary U0028 fault on the MOST bus prevents them from hearing from the radio module, which is the bus master.
• U0186 — This code means 'Lost Communication with Audio Amplifier'. If the vehicle is equipped with a premium sound system, the amplifier is a module on the MOST ring. If it fails, other modules will log this code along with the primary U0028.

Technical Service Bulletins (TSBs) & Recalls

• PIC6073E: A general GM bulletin that announces the release of the EL-51578 MOST Bus Diagnostic Tool Kit and instructs technicians to use it for diagnosing DTC U0028 and related symptoms like a blank radio display. It advises checking basic power/ground to modules first. [15, ⭐ MANUFACTURER TSB — highest authority]
• PI1149A: Provides detailed diagnostic advice for blank radio displays and no audio across many 2014-2018 GM vehicles. It explains how to use the bypass tool, and notes the difference in symptoms if the bus fails at startup (blank screen) vs. while driving (clock disappears). [8, ⭐ MANUFACTURER TSB — highest authority]

Platform-Specific Known Issues

• HMI Module Location: On the Gen 2 Volt (2016-2019), the HMI module is a silver box located behind the glove compartment, making it relatively easy to access for diagnosis with a bypass loop. On the Gen 1 Volt (2011-2015), it is located deeper in the center stack behind

Mechanic-Grade Diagnostic Values

• MOST Bus Optical Signal — expected: A visible red light emitted from the 'out' port of a functioning module's fiber-optic connector when the system is active.. Failure: No red light coming from a module indicates it is not receiving the signal from upstream or it has failed internally and is not transmitting.
• MOST Control (ECL) Circuit Voltage — expected: A steady 9-13 V when the bus is functioning correctly.. Failure: When DTC U0028 is current, the voltage will toggle between 9-13 V and 0 V, indicating the system is trying to re-establish communication.

Hidden / Shadow Codes Worth Checking

• Surrogate MOST Master Node Upstream Position: This is not a DTC, but a live data parameter in the Radio module viewable with a GDS2 scan tool. It displays a number corresponding to the module just *before* the communication break in the ring. For example, if the CD player (node 2) fails, the HMI (node 3) might become the surrogate master, and the upstream position would point to the CD player as the fault. (see via GM GDS2 scan tool, in the Radio module data list.)
• Number of MOST Communication Breaks: A GDS2 data parameter in the Radio module. A value greater than 0 indicates a complete break in the ring. A value of '0' when U0028 and U0029 are present can indicate the ring has integrity, but a module is not communicating correctly internally. (see via GM GDS2 scan tool, in the Radio module data list.)

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Radio Data Display -> MOST Bus Data — This is the primary diagnostic step after retrieving codes. Use this to view the 'Surrogate MOST Master Node Upstream Position' and 'Number of MOST Communication Breaks' to pinpoint the location of the fault in the ring before physically accessing modules.
• GDS2 with SPS (Service Programming System): Module Programming — Required after replacing the HMI module or Radio/Tuner module. The new module must be programmed with the vehicle's VIN and specific configuration to function.
• GDS2: Data Bus Diagnostic Tool — This function within GDS2 can actively poll the communication buses to determine which modules are responding and which are not, helping to confirm which module has dropped off the network.

Wiring & Ground Locations

• Amplifier (Bose) — Under the trunk floor, near the 12V battery and Accessory Power Module (APM).. The amplifier is a node on the MOST bus ring. A failure of this module or its connector will break the ring and cause U0028. Its location in the trunk makes it susceptible to water damage if any leaks are present.
• HMI Module (Gen 2) — Behind the glove box. The glove box assembly must be removed for access.. This is the most common failure point. Knowing its location is critical for diagnosis with a bypass loop and for replacement.
• HMI Module (Gen 1) — Located in the center stack, behind the main infotainment controls and display.. Access is more involved than on Gen 2 vehicles, often requiring removal of center console trim and the integrated center stack (ICS) faceplate.
• Gen 1 (2013-2015) Head Unit Connector — Rear of the head unit in the center stack.. Pin 28 (L-GN wire) is the Low Speed GMLAN Serial Data line, while Pin 44 (RD/YE) is Battery Positive Voltage and Pin 38 (BK) is Ground. Verifying power, ground, and GMLAN communication at this connector is a key step if the radio is suspected to be faulty.

Real Owner Repair Stories

• iATN (International Automotive Technicians' Network) (2015 Chevrolet Silverado (shares MOST architecture)) — MyLink display was dark, radio would not play, all control buttons were non-functional. Codes U0028 and U0029 were present.
  ❌ Tried (didn't work) The technician correctly avoided random power/ground checks because multiple module failures pointed to a network issue.
  ✅ What actually fixed it Using a GDS2 scan tool, the tech noted the 'Surrogate MOST Master Node Upstream Position' was 2. On this vehicle, the ring order was Radio -> CD Player -> HMI -> IPC. Counting back two positions from the end of the ring (IPC, then HMI) pointed to the CD player as the fault. The tech could not communicate with the CD player. Jumping the data lines at the CD player connector with a bypass loop restored all infotainment functions. The failed CD player was the cause.
• MHH Auto forum user 'Jose3903' (2016 Chevrolet Impala (shares MOST architecture)) — Black screen, no audio, and code U0028-00 stored.
  ❌ Tried (didn't work) Initial diagnosis was unable to pinpoint the specific faulty module.
  ✅ What actually fixed it After using a bypass loop on other modules, the CD player was identified as the faulty node. Replacing it with a used unit from a junkyard restored screen and audio function, confirming the CD player had failed internally and broken the MOST ring.

When the Usual Fixes Don't Work

• While the HMI module is the most frequent cause of U0028, it is not the only one. A detailed diagnostic case on a similar GM platform confirmed that a failed CD player was the sole cause of the MOST bus failure. The technician used GDS2 scan tool data to identify the break in the ring was at the CD player before using a bypass loop to confirm. This highlights the importance of not defaulting to HMI replacement without performing a full ring diagnosis.

OEM Part Supersession History

• 84089011 → This part is the latest in a chain. It replaces older part numbers 23212442, 23364950, 23415899, and 84028492. — Standard part evolution for hardware/software revisions.
  Heads up: This part is for Gen 2 Volts (approx. 2016-2017) and is not compatible with Gen 1. It is also specific to certain RPO codes (IO5/IO6 for navigation).
• 84546904 → 84513027. Part 84546904 is listed as discontinued. — Part discontinuation and replacement.
  Heads up: This part is for later Gen 2 Volts (approx. 2017-2018). Using an incorrect HMI module, even if it physically fits, will not work as the data streams and programming are different. Always verify the part number or have it programmed to the VIN.

Model Year Variations Within This Range

• 2013: The radio (tuner) may need to be reprogrammed with the latest SPS calibration to make the critical 'Surrogate MOST Master Node Upstream Position' parameter visible on a GDS2 scan tool. Without this update, the parameter may not be displayed, making intermittent fault diagnosis much more difficult.
• 2013-2015 vs 2016-2018: The physical location of the HMI module is different. On Gen 1 (2013-2015), it is in the center stack. On Gen 2 (2016-2018), it is located behind the glove box, which is significantly easier to access for diagnosis and replacement.