U0028 on 2013-2018 Chevrolet Trax: Infotainment Network Fault Causes and Fixes

What's Unique About the 2013-2018 Chevrolet TRAX

The Chevrolet Trax and its platform-mate, the Buick Encore, use the MOST bus for their infotainment systems. This system operates in a ring topology, meaning if one component or wire in the loop fails, the entire system goes down. While other larger GM trucks have a well-documented TSB for a pinched wiring harness causing this issue, the problem on the Gamma II platform (Trax/Encore) is more commonly associated with an internal electronic failure of one of the modules on the network, such as the radio (tuner) or the Human Machine Interface (HMI) module.

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/radio screen, especially on startup
• No audio from the radio or other media sources
• Infotainment system controls are unresponsive
• Parasitic battery drain leading to a dead battery
• Loss of audible chimes (turn signals, warnings) which are generated by the infotainment system

Most Likely Causes

1. Failed Human Machine Interface (HMI) Module 🔴 High Probability → Shop Infotainment Display The HMI module, which acts as the brain for the display and user inputs, is a critical and complex node on the MOST bus. Internal electronic failure is common and will break the communication ring.
   How to confirm: A technician will use a MOST bypass loop to temporarily remove the HMI module from the network ring. If communication is restored to the other modules (e.g., the radio audio returns and the 'Audio Off' message on the instrument cluster disappears), the HMI module is confirmed as the fault.
   Typical fix: Replace the HMI module. 🎬 Watch this walkthrough on HMI module replacement and programming This part is VIN-specific and requires programming by a dealer or a qualified shop with GM software.
   Est. part cost: $250-$500
2. Failed Radio (Tuner) Module 🟡 Medium Probability → Shop Audio System The radio acts as the master controller for the MOST bus, initiating the 'wake-up' signal for the network. An internal fault can take down the entire system.
   How to confirm: Diagnosis is a process of elimination. After using a bypass loop to confirm all other modules on the ring are functional, the radio becomes the primary suspect. The radio itself cannot typically be bypassed with a standard loop tool. A scan tool showing 'Audio Off' in the instrument cluster data is another strong indicator.
   Typical fix: Replace the radio/tuner module. This part also requires programming to the vehicle's VIN.
   Est. part cost: $300-$700
3. Damaged or Loose MOST Bus Wiring/Connectors ⚪ Low Probability While less common on the Trax than on larger GM trucks, wiring can still be damaged behind the dash or at module connectors due to vibration or previous repairs.
   How to confirm: Visually inspect the fiber optic or electrical wiring harnesses connected to the radio, HMI module, and any other components on the MOST bus. Check for secure connections and any signs of chafing, pinching, or corrosion.
   Typical fix: Repair the damaged section of the wiring harness or clean and re-seat the connector.
   Est. part cost: $10-$50

Rare But Worth Checking

• Failed CD/Media Disc Player: → Shop Audio System If equipped, the CD player is another module in the MOST ring. An internal failure can break the communication loop. In a documented case on a similar GM vehicle, a technician used scan tool data to identify the CD player as the faulty node, then used a bypass loop to confirm the diagnosis and restore radio function.
• Failed Instrument Panel Cluster (IPC): → Shop Instrument Cluster The IPC is also a node on the MOST bus in some configurations. An internal failure can break the ring, causing U0028. This would be diagnosed using the same bypass loop procedure as other modules.
• Power or Ground Issue to a Module: Before condemning an expensive module, it's crucial to verify it is receiving proper power and ground. A blown fuse or a bad ground wire can prevent a module from powering on, which has the same effect as an internal failure, breaking the ring and setting a U0028 code.

Diagnosis Steps

1. Connect a professional scan tool capable of reading GM-specific codes and data.
2. Verify that code U0028 is present and active. Note any other 'U' codes, especially U0029.
3. Confirm the primary symptoms: blank screen and no audio at startup.
4. Using the scan tool, access the radio module data. Check the 'Number of MOST Communication Breaks' and 'Surrogate MOST Master Node Upstream Position' PIDs. This data can help identify which module is causing the break in the ring.
5. Gain access to the modules on the MOST ring (typically the radio, HMI module behind the glove box, and CD player if equipped).
6. Using a MOST bus bypass loop (e.g., GM tool EL-51578), systematically bypass one module at a time. 🎬 See how to use a bypass loop for simple testing Start with the easiest module to access, like the HMI or CD player.
7. After bypassing a module, cycle the ignition and check if infotainment functions are restored. For example, if you bypass the HMI module and the radio audio returns, the HMI module is the faulty component.
8. Before replacing a module confirmed as faulty by the bypass test, check its power and ground connections to rule out a simple wiring issue.
9. If bypassing all accessible modules does not restore function, inspect the wiring between modules for damage.
10. If all other modules and wiring are good, the fault likely lies with the master module (the radio/tuner), which cannot be bypassed with a standard loop.
11. Once the faulty component is identified, replace it. Note that replacement modules like the HMI or radio require VIN-specific programming by a dealer or specialist.

Parts You'll Likely Need

• Human Machine Interface (HMI) Module (OEM #84028492, 84156701, 84513027 (Examples, verify by VIN)) — This is a very common failure point on the MOST network that will cause a total communication breakdown and trigger U0028.
  Trusted brands: ACDelco
  OEM price range: $250-$500
  Aftermarket price range: $200-$400
• Radio / Tuner Module — As the master of the MOST bus, an internal failure in the radio will bring down the entire infotainment system.
  Trusted brands: ACDelco
  OEM price range: $300-$700
  Aftermarket price range: $250-$550
• MOST Bus Bypass Loop (OEM #EL-51578) — This is an essential diagnostic tool for identifying the specific failed module on the ring network. It is not a permanent repair part but is required for accurate diagnosis.
  OEM price range: $20-$40
  Aftermarket price range: $10-$25

Related Codes That Often Appear With This One

• U0029 — This code also indicates a MOST bus performance issue. While U0028 often points to a complete break in the ring ('Bus Off'), U0029 can indicate the ring has integrity but a specific module is not communicating correctly. They frequently appear together and are diagnosed using the same procedures.

Technical Service Bulletins (TSBs) & Recalls

• PIC6073E: Recommends reviewing MOST bus operation and using specific diagnostic procedures and tools for DTC U0028. [⭐ MANUFACTURER TSB — highest authority]
• PI1149A: Provides diagnostic steps for a blank screen/no audio condition, identifying it as a MOST bus failure (U0028) and recommending the use of a bypass loop. [⭐ MANUFACTURER TSB — highest authority]

Platform-Specific Known Issues

• TSB PIC6073E: Official Diagnostic Guidance: This TSB specifically advises technicians to review the Media Oriented Systems Transport (MOST) bus description and use the proper diagnostic procedures and tools (like the EL-51578 bypass loop) when encountering code U0028 on these vehicles, confirming the nature of the fault. [⭐ MANUFACTURER TSB — highest authority]
• TSB PI1149A: Blank Screen Diagnostic Aid: This Preliminary Information bulletin provides a detailed diagnostic aid for the exact symptom of a blank infotainment display with no audio. It confirms that this condition at startup points to a MOST bus failure, references DTCs U0028/U0029, and instructs technicians on using the bypass loop tool for diagnosis. [⭐ MANUFACTURER TSB — highest authority]

Mechanic-Grade Diagnostic Values

• Module Power Supply Voltage — expected: 12.0 - 14.5 V (Key On). Failure: Low or no voltage at a module's power pin indicates a wiring, fuse, or ground issue, not necessarily an internal module fault.
• Module Ground Pin Resistance — expected: < 0.5 Ω to chassis ground. Failure: High resistance points to a corroded or loose ground connection, which can prevent a module from communicating.

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Radio > MOST Data — Use this to view critical parameters like 'Number of MOST Communication Breaks' and 'Surrogate MOST Master Node Upstream Position'. This data helps pinpoint the location of the ring break before physically accessing modules.
• GDS2 (GM Global Diagnostic System 2): Data Bus Diagnostic Tool — This function actively polls all modules on the network to create a list of which ones are communicating. It's a quick way to confirm which module has dropped off the bus and is causing the U0028 code.
• SPS (Service Programming System): Module Programming and Setup — This is required after replacing the HMI or Radio module. It programs the new module with the vehicle's specific VIN and configuration to prevent a 'theft locked' state and ensure full functionality.

Wiring & Ground Locations

• Fuse F32 (Passenger Cabin Fuse Box) — In the fuse box located in the passenger's cabin, under the steering wheel.. This 15A fuse provides the main power to the radio. A failure of this fuse will cause the radio (the MOST bus master) to lose power, breaking the ring and setting U0028.
• Fuse F33 (Passenger Cabin Fuse Box) — In the fuse box located in the passenger's cabin, under the steering wheel.. This 10A fuse provides power to the infotainment display. While a failure here might not cause U0028 on its own, it should be checked when diagnosing a blank screen.
• Fuse F3 (Trunk Fuse Box) — In the fuse box located in the trunk/rear cargo area.. This 25A fuse provides power to the amplifier (if equipped). If the vehicle has a premium sound system, the amplifier is a module on the MOST ring. A blown fuse will take the amp offline and break the ring.

Real Owner Repair Stories

• MHH Auto forum user (2016 Chevrolet Impala (similar MOST architecture)) — Black screen, no audio, code U0028-00 present.
  ❌ Tried (didn't work) Initial research pointed to HMI, radio, amp, or cluster, but the user wanted to diagnose before replacing parts.
  ✅ What actually fixed it The user found the issue was the CD player module. After replacing it with a used unit from a junkyard, the screen turned on again. (Note: The replacement part then showed a 'theft locked' message, which requires VIN programming to resolve).
• Automotive Diagnostics & Programming YouTube Channel (Buick Verano (similar MOST architecture)) — Radio inoperative, cluster displays 'Audio Off', blank center screen, U0028 in radio, U0029 in HMI.
  ❌ Tried (didn't work) The video focused on direct diagnosis rather than listing failed attempts.
  ✅ What actually fixed it The technician used a MOST bypass loop on the fiber-optic connector for the CD player. The radio and screen immediately began working, confirming the CD player had failed internally and was the cause of the ring break.

OEM Part Supersession History

• 84156701 → 84296482 — Standard part revision by the manufacturer for improvements or supplier changes.
  Heads up: When replacing an HMI module, the replacement part, whether new or used, must be programmed to the vehicle's VIN using GM's SPS software to avoid a 'theft locked' condition.

Model Year Variations Within This Range

• 2013-2016: These earlier models are more likely to use HMI 2.0 modules. The 2013 model year, in particular, may require a radio software update to display all necessary diagnostic parameters for U0028 on a GDS2 scan tool, as noted in TSB PI1149A.
• 2017-2018: Following the 2017 model year refresh, these vehicles are equipped with the newer HMI 2.5 module, which supports features like Android Auto/Apple CarPlay. While the diagnostic principle for U0028 is the same (MOST ring break), the specific HMI part number will be different from earlier years.