U0028 on 2013-2017 GMC Yukon Denali: MOST Bus Communication Fault Causes and Fixes

What's Unique About the 2013-2017 Gmc YUKON DENALI

This year range spans two Yukon generations: the GMT900 (2013-2014) and the K2XX (2015-2017). Both use a MOST bus for their infotainment systems, but the wiring routes and specific failure points differ. A well-documented issue on the K2XX platform (2015-2017) is a pinched wire harness behind the left side of the instrument panel, as cited in GM Technical Service Bulletin #PIT5288H. This TSB notes the harness can get crushed between the I/P mounting bracket and the vehicle body near the parking brake pedal. For the earlier GMT900 platform, TSB #PIC6073E also points to MOST bus diagnostics, indicating these network issues are a known characteristic of the Yukon Denali across these years. The K2XX platform uses an HMI 2.0 or 2.5 module architecture, which is fundamentally different from the later HMI 3.0 systems that use Automotive Ethernet instead of a MOST bus.

Diagnostic Flowchart

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

Generation note: The 2013-2017 range covers the end of the GMT900 platform (2013-2014) and the beginning of the K2XX platform (2015-2017). While both use a MOST bus, the K2XX models are specifically called out in TSBs for a pinched wire harness behind the dash as a common cause. The diagnostic principles are similar for both generations, but the HMI module behind the glovebox is a more common failure point on the K2XX models. The HMI modules also differ, with 2014-2015 models using HMI 2.0 and 2016-2017 models using HMI 2.5, which added features like Apple CarPlay and Android Auto.

Symptoms You May Notice

• Blank infotainment/radio screen (screen may be black but still backlit)
• No audio from the speakers, including chimes and turn signal sounds
• Radio or navigation system is inoperative
• Intermittent dead battery or no-start condition
• Loss of function for steering wheel audio controls
• "Audio Off" message on the instrument cluster
• Bluetooth, voice control, and USB audio are non-functional
• Backup camera fails to display (though sometimes it may still work while the radio is off)

Most Likely Causes

1. Pinched or Damaged Wire Harness 🔴 High Probability A GM Technical Service Bulletin (#PIT5288H) specifically identifies a pinched wire harness on the left side of the instrument panel as a cause for this code on 2015-2017 models. The harness gets crushed between the I/P dash mounting bracket and the body, often near the parking brake pedal area.
   How to confirm: Visually inspect the wiring harness from under the dash, looking up and to the left of the steering column, for any signs of pinching, chafing, or damage against the metal dash support bracket. This may require removing the I/P fuse block cover for a better view.
   Typical fix: Loosen the left I/P dash mounting bracket bolts to free the harness. Open the harness loom, repair any severed or chafed wires, and properly insulate them. Reroute the harness to prevent it from being pinched again before tightening the bracket.
   Est. part cost: $10-$50
2. Failed Human Machine Interface (HMI) Module 🟡 Medium Probability The HMI module, which controls the display screen and is located behind the glovebox on K2XX models, is a critical and very common failure point on the MOST bus. An internal failure can break the communication ring, causing a blank screen and code U0028. These modules are also known to fail after power interruptions, like a battery replacement.
   How to confirm: Use a MOST bypass loop tool (EL-51578) to bypass the HMI module. If communication is restored to the other modules (e.g., the radio starts working and audio returns), the HMI module is faulty. A professional scan tool will also show the HMI module is not communicating. Before condemning the module, verify battery voltage on the power feed wire (often red/violet) and ground at the main connector.
   Typical fix: Replace the HMI module. This part is VIN-locked and requires programming by a dealer or a qualified shop with GM software (SPS) after installation. Some aftermarket vendors sell pre-programmed modules.
   Est. part cost: $250-$600
3. Failed Radio or CD Player Module 🟡 Medium Probability The radio is the master of the MOST bus, and the CD player is another node in the ring. An internal failure in either of these components will take down the entire network. In one documented case on a platform mate, a technician bypassed a non-responsive CD player, which immediately restored radio and screen function, proving the CD player was the sole cause.
   How to confirm: Use a MOST bypass loop to individually bypass the radio and CD player. If the network comes back online when one is bypassed, that module is the cause of the failure. If bypassing the CD player restores function, the CD player has failed. The radio itself cannot be bypassed with the tool as it is the master.
   Typical fix: Replace the faulty module. The radio will likely require programming. If the CD player is faulty and not needed, some owners choose to permanently install the bypass loop to eliminate it from the network.
   Est. part cost: $200-$800

Rare But Worth Checking

• Damaged Fiber-Optic Cable: If the system uses fiber optics, the cables are fragile. They can be broken or bent too sharply during unrelated repairs under the dash or seats, causing a complete loss of communication.
• Failed Amplifier: If the vehicle is equipped with a premium sound system, the amplifier is also a module on the MOST bus. Though less common to fail than the head unit or HMI, it can still break the ring. Bypassing it with a loop tool is the method for confirmation.
• Loose Connector at HMI Module: In some cases, the main blue connector at the HMI module behind the glovebox can become loose or have a poor pin connection. Wiggling this connector bundle while the system is on may cause the screen to flicker, indicating a connection issue rather than a failed module.

Diagnosis Steps

1. Perform a full vehicle DTC scan to see which modules are reporting 'no communication' and to check for other codes like U0029 or U0184.
2. If available, use an advanced scan tool (like GM's GDS2) to check the 'Surrogate MOST Master Node Upstream Position' data in the radio module. This data helps pinpoint the location of the break in the ring, as described in TSB #PI1149A.
3. Visually inspect the known problem area for a pinched wiring harness at the left side of the instrument panel, between the dash mounting bracket and the body, as per TSB #PIT5288H.
4. If no wiring damage is found, obtain a MOST bus bypass loop (GM tool EL-51578).
5. Systematically connect the bypass loop at each accessible module in the MOST ring (e.g., CD player, HMI module, amplifier). The ring order is typically Radio -> CD Player -> HMI -> Amplifier -> Instrument Cluster -> Radio.
6. After bypassing a module, cycle the ignition and see if the infotainment system powers on. If it does, and the U0028 code changes from 'current' to 'history', the bypassed module is the one that has failed.
7. Once the faulty module is identified, check for proper power and ground at its connector before condemning the module itself.
8. If a module is confirmed to be faulty, replace it. Note that the HMI and Radio modules require VIN-specific programming (SPS) after installation to function.

Parts You'll Likely Need

• Human Machine Interface (HMI) Module (OEM #23212438, 84096815, 84296480, 84131941, 84156701) — This module, located behind the glove box, controls the screen and is a very common failure point on the K2XX MOST network, causing a total communication breakdown.
  Trusted brands: ACDelco
  OEM price range: $400-$700
  Aftermarket price range: $250-$500
• Radio/Tuner Module — As the master of the MOST bus, an internal failure in the radio will bring down the entire infotainment system. It is a required component for the network to function.
  Trusted brands: ACDelco
  OEM price range: $500-$900
  Aftermarket price range: $300-$600
• MOST Bus Bypass Loop (OEM #EL-51578) — This is an essential diagnostic tool (not a repair part) used to isolate the faulty module in the fiber-optic or electrical ring. It is required for accurate diagnosis.

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 sometimes mean the ring integrity is present but communication is still failing, which can help in diagnosis.
• U0184 — This code means 'Lost Communication with Radio'. Since the radio is the master module on the MOST bus, a U0028 fault will almost always be accompanied by a U0184 code.
• U0151 — This code for 'Lost Communication with Restraints Control Module' can appear with U0028 if the pinched wiring fault described in TSB #PIT5288H affects multiple networks simultaneously.

Technical Service Bulletins (TSBs) & Recalls

• PIT5288H: Addresses multiple communication DTCs, including U0028, caused by a pinched wire harness between the left I/P dash mounting bracket and the body.
• PIC6073E: Recommends reviewing MOST bus description and operation for diagnosing U0028 and using the EL-51578 diagnostic tool kit.
• PI1149A: Provides diagnostic aids for a blank radio display with code U0028, including checking the 'Surrogate MOST Master Node' parameter.

Platform-Specific Known Issues

• TSB #PIT5288H notes that on 2015-2017 models, a pinched wire harness at the left instrument panel can cause U0028 along with a dead battery and multiple other communication codes like U0151 and U0077.
• TSB #PIC6073E directs technicians to review MOST bus operation and diagnostic procedures for code U0028, confirming this is a known issue requiring specific diagnostic tools and knowledge.
• TSB #PI1149A provides advanced diagnostic advice, suggesting technicians use a scan tool to look for the 'Surrogate MOST Master Node Upstream Position' PID, which can help locate the break in the ring without having to physically access every module first.

Mechanic-Grade Diagnostic Values

• MOST Bus Wake-Up Signal — expected: A 12-volt signal that is pulled to ground by the radio module for approximately 100 milliseconds to signal other modules to wake up.. Failure: An open or high resistance in this circuit can prevent the wake-up signal, causing a U0028 code.
• HMI Module Power/Ground — expected: Battery voltage (approx. 12.6V) at the power feed pin (often a red/violet wire) and good continuity to ground at the ground pin (Pin 20 on Connector X1 for 2015-2020 models).. Failure: Low or no voltage, or high resistance to ground, indicates a wiring issue, not a failed HMI module.

Hidden / Shadow Codes Worth Checking

• U0028-88: Bus Off. This symptom byte indicates a module has detected a severe error and has stopped transmitting on the MOST bus to prevent further disruption. (see via GM GDS2 or equivalent professional scan tool.)
• U0028 71: Invalid Serial Data Received. This indicates that data is being received, but it is corrupted or in an unexpected format, pointing more towards a module fault than a complete wiring break. (see via GM GDS2 or equivalent professional scan tool.)
• U0028 sym00: This is a standard symptom byte indicating a general MOST bus fault, often called out in GM diagnostic procedures. (see via GM GDS2 or equivalent professional scan tool.)

Scan Tool Commands That Help

• GDS2: Radio Data > 'Number of MOST Communication Breaks' — Use this to determine the nature of the fault. A value of '1' or more indicates a physical break in the ring. A value of '0' when U0028/U0029 is present suggests the ring is intact but a module is failing internally.
• GDS2: Radio Data > 'Surrogate MOST Master Node Upstream Position' — This data PID helps locate the fault. As described in TSB PI1149A, the value indicates how many nodes upstream from the master the break occurred, allowing a technician to identify the faulty module without having to bypass every single one.
• GDS2: Service Programming System (SPS) — This function is required after replacing the HMI or Radio module. It downloads the correct, VIN-specific software and calibration files to the new module, allowing it to communicate with the vehicle.

Wiring & Ground Locations

• Left I/P Dash Mounting Bracket — Under the driver's side dash, near the parking brake pedal assembly and I/P fuse block cover.. This is the specific location identified in TSB #PIT5288H where the main dash harness, containing the MOST bus wires, is known to get pinched or chafed against the vehicle body, causing an open or short in the communication ring.
• G218 — Under the driver's side of the instrument panel, near the A-pillar. The trim must be removed for access.. This is a major ground point for the Body Control Module (BCM) and other interior electronics, including the Radio and Instrument Panel Cluster. A loose or corroded connection here can cause intermittent communication faults across multiple modules.
• HMI Module Connector X1 — On the Human Machine Interface module, located behind the glove box on 2015-2020 models.. This is the main connector for the HMI. Pin 10 is the battery positive voltage feed, and Pin 20 is the ground. Verifying power and ground here is a critical step before condemning the module.

Real Owner Repair Stories

• iATN Diagnostic Forum (2015 Chevrolet Silverado) — MyLink display is dark, radio and control buttons are non-functional. Codes U0028 in radio and U0029 in HMI were present.
  ❌ Tried (didn't work) Initial visual inspection.
  ✅ What actually fixed it GDS2 scan data showed 'Surrogate MOST Master Node Upstream Position' of 2. The tech counted backwards in the ring (Radio->CD->HMI->IPC) and identified the CD player as the likely fault. The tech could not communicate with the CD player. After removing the CD player and installing a bypass loop, the display and radio function returned to normal. The root cause was an internal failure of the CD player module.
• YouTube user 'noonespecial' (2015 Chevrolet Silverado) — Blank screen, no radio, no sound. Backup camera still worked. Codes U0028 and U0029 were present.
  ❌ Tried (didn't work) Replacing the broken screen with a new one did not solve the problem.
  ✅ What actually fixed it The CD/disc player module had failed. A technician removed the CD player and used a bypass loop on its connector, which immediately restored radio and screen functionality.
• YouTube video by 'The Car Lab' (2018 Chevrolet Suburban) — Radio not working, screen is off, multiple communication codes including U0028.
  ❌ Tried (didn't work) Using a MOST bypass loop on the CD player did not restore system function.
  ✅ What actually fixed it The technician moved the bypass loop to the next module in the ring, the Human Machine Interface (HMI) module. Bypassing the HMI restored communication to the rest of the system, proving the HMI module was the faulty component.

OEM Part Supersession History

• 84131941 → 84296480 — Standard part revision and update by the manufacturer.
  Heads up: This part number is for an HMI 2.5 module, typically found in 2016-2017 models. It is not directly compatible with 2013-2015 models which use an HMI 2.0 module. Upgrading from 2.0 to 2.5 requires replacing the radio module and USB hub as well.

Model Year Variations Within This Range

• 2013-2014 (GMT900): These models use a different infotainment architecture than the 2015+ K2XX models. While they have a MOST bus, the common failure points are less focused on the pinched harness and more on general module failures. TSB #PI1149A notes that some of these early models may require a radio software update to even display the necessary diagnostic parameters on a GDS2 scan tool.
• 2015-2017 (K2XX): These models are specifically prone to the pinched wire harness issue described in TSB #PIT5288H. They also use HMI 2.0 (2015) and HMI 2.5 (2016-2017) modules, which are a very common failure point located behind the glovebox.