U0028 on 2013-2018 GMC Sierra 1500: Infotainment Network Fault Causes and Fixes

What's Unique About the 2013-2018 Gmc SIERRA 1500

The 2013-2018 Sierra spans two distinct generations (GMT900 for 2013 and K2XX for 2014-2018), both of which can experience this issue. The K2XX platform (2014-2018) is particularly known for a specific wiring issue where a main harness can get pinched by a dash bracket under the driver's side dash, causing a multitude of communication codes, including U0028. This makes 🎬 Watch: Diagnosing blank displays and U0028 codes on GM trucks checking that specific wiring location a primary diagnostic step for these model years. For both generations, the issue is almost always isolated to the infotainment system components and their dedicated MOST network.

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 end of the 2nd generation (2013, GMT900) and the beginning of the 3rd generation (2014-2018, K2XX). While the MOST bus concept is similar, the specific modules and wiring locations can differ. A well-documented cause for 2014-2018 models is a pinched harness near the left I/P dash mounting bracket, as noted in TSB PIT5288H. The 2013 models are covered under a more general MOST bus diagnostic TSB, PIC6073E.

Symptoms You May Notice

• Blank radio or infotainment display (screen may be completely black or display a message like 'Calibrate Device').
• No audio from the radio, but chimes may still work.
• Radio controls and steering wheel controls are inoperative.
• Intermittent "No Fob Detected" message.
• Dead battery due to a parasitic draw from a module not shutting down properly.
• Multiple other communication codes may be present, especially U0029.
• HVAC controls may go blank or become inoperative.
• Backup camera may still function when the screen is otherwise blank.
• On startup, the screen may briefly show a logo before going blank or locking up.

Most Likely Causes

1. Pinched or Damaged Dash Wiring Harness 🔴 High Probability A GM Technical Service Bulletin (PIT5288H) specifically identifies a location on 2014-2018+ models where the dash harness can be pinched between the left instrument panel mounting bracket and the body. This can cause shorts or opens in the communication wires for the MOST bus and other systems. The damage can be hard to see without pulling the harness away from the bracket.
   How to confirm: Visually inspect the wiring harness under the driver's side dash, near the I/P fuse block and parking brake pedal assembly. TSB PIT5288H shows the harness can be pinched at the upper or lower portion of the metal I/P mounting bracket. Look for any signs of chafing, crushing, or damage where the harness passes near these metal edges. You may need to loosen the bracket bolts to free the harness for a full inspection.
   Typical fix: Free the pinched harness, open the loom, and repair any damaged wires individually using solder and heat shrink or appropriate connectors. Reroute the harness to prevent future damage, potentially using split loom tubing for extra protection.
   Est. part cost: $5-$25 for wiring repair supplies.
2. Failed Human Machine Interface (HMI) Module 🟡 Medium Probability The HMI module, which acts as the brain for the display screen and integrates various inputs, is a central node on the MOST bus. Internal failure, sometimes from component breakdown or even failed software updates, can disrupt the entire network. The HMI module is located behind the glove box.
   How to confirm: This is best confirmed by a professional using a scan tool to see if the HMI module is offline. A diagnostic bypass tool (like GM's EL-51578) can be used to loop out the HMI; if communication is restored to other modules (e.g., the radio starts working, though the screen remains blank), the HMI is faulty. If the HMI is bypassed, the display will be inoperative.
   Typical fix: Replacement of the HMI module. This part is VIN-locked and requires programming by a dealer or a qualified shop with GM's Service Programming System (SPS). Unlocked, pre-programmed modules are available from third-party sellers but require providing your VIN.
   Est. part cost: $250-$600
3. Failed Radio or CD Player Module ⚪ Low Probability Like the HMI, the radio (tuner) and CD player are nodes in the MOST ring. The radio acts as the master, and an internal fault in either unit can break the communication loop. The CD player is a common point of failure that can take down the whole system.
   How to confirm: Similar to the HMI, diagnosis involves using a scan tool and MOST bypass tools to isolate the faulty module. If bypassing the CD player restores function to the screen and radio controls, the CD player is the culprit. A technician can also use scan tool data to see which node in the ring is reporting the communication break.
   Typical fix: Replace the failed module. The radio often requires programming after installation. If the CD player is the cause, some owners choose to simply bypass it permanently to restore radio function without replacing the player.
   Est. part cost: $200-$700

Rare But Worth Checking

• Poor Ground at G218: A poor ground connection at G218, located under the driver's side dash trim near the A-pillar, can cause a wide range of electrical issues, including communication faults. The insulation mat can sometimes get trapped under the ground terminal, causing a weak connection. This should be inspected, cleaned, and tightened, especially if multiple unrelated electrical symptoms are present.
• Failed Instrument Panel Cluster (IPC): The IPC is also a node on the MOST bus. While less common to fail in a way that brings down the network, it is a possibility and would be diagnosed by bypassing it with the proper tool. If the IPC is bypassed, the DIC audio page and steering wheel controls will become inoperative, but the radio may function.
• Low Battery Voltage: While often a symptom (parasitic draw from a faulty module), a weak or failing battery can itself cause modules to malfunction and trigger communication codes during startup. Always verify battery health first before chasing down complex network issues.

Diagnosis Steps

1. Check Battery Health: Ensure the battery has a full charge (12.4V+ resting) and passes a load test. Low voltage can cause spurious communication codes.
2. Full Vehicle Scan: Use a quality OBD-II scanner like GM's GDS2 to check for all codes in all modules. Note any other 'U' (communication) codes, especially U0029, and check for any symptom bytes associated with the codes.
3. Inspect Dash Wiring (2014-2018 models): Following TSB PIT5288H, carefully inspect the wiring harness under the driver's side dash for signs of being pinched by the metal I/P bracket. This is a very common failure point and should be checked before replacing parts. The harness may be pinched at the upper or lower part of the bracket.
4. Inspect Ground G218: While in the driver's footwell, inspect ground G218. Ensure the nut is tight and that the dash insulation material is not trapped between the ground eyelet and the body stud.
5. Repair Wiring: If any damage is found, disconnect the battery, repair the affected wires, and properly insulate and secure the harness away from the bracket.
6. Professional Diagnosis (If no wiring damage): If the wiring is intact, the next step is to diagnose the MOST network itself. This requires a scan tool to see which modules are offline and a MOST bypass tool kit (like GM tool EL-51578) to systematically bypass each module (HMI, CD player, IPC, etc.) on the ring until communication is restored. The radio is the master and cannot be bypassed.
7. Isolate and Replace: The module that, when bypassed, allows the rest of the system to work (and changes the U0028 code from 'current' to 'history') is the faulty component and needs to be replaced. Remember that replacement modules like the HMI and radio require professional programming (SPS) to function correctly with the vehicle's VIN and options.

Parts You'll Likely Need

• Human Machine Interface (HMI) Module (OEM #23228498 (For 2015-2016 models, IO5/IO6, part numbers are superseded often, always verify by VIN)) — This module is a common point of failure that will take down the entire MOST network, causing the U0028 code and blank screen. It requires VIN-specific programming upon replacement.
• MOST Bus Bypass Loop (OEM #Part of kit EL-51578) — A diagnostic tool, not a repair part. This fiber optic or electrical loop is essential for isolating which module on the MOST ring has failed.

Related Codes That Often Appear With This One

• U0029 — This code is also a MOST bus communication fault and is frequently set alongside U0028. U0029 can indicate a communication error is occurring but the ring integrity is still present, which can help pinpoint the issue to a specific module rather than a complete break.
• U0140 — Loss of Communication with Body Control Module (BCM). This can occur if the pinched harness issue affects multiple communication circuits, not just the MOST bus. This code is explicitly mentioned in TSBs related to the pinched dash harness.
• U0151 — Loss of Communication with Restraints Control Module (Airbag). This is another code often cited in TSBs related to the pinched dash harness, indicating a more widespread electrical issue caused by the same chafed wiring.
• B127B — Steering Wheel Controls Circuit fault. This can be a direct result of the MOST bus failure, as the steering wheel controls communicate through this network.

Technical Service Bulletins (TSBs) & Recalls

• PIT5288H: Covers a wide range of electrical issues including no audio, blank screen, and various communication DTCs (including U0028/U0029) caused by a pinched dash harness on 2014-2020 GM trucks and SUVs. It provides images and instructions for locating and repairing the damaged wiring.
• PIC6073E: A diagnostic tip bulletin that guides technicians on using the EL-51578 MOST Bus Diagnostic Tool Kit to diagnose U0028 and related infotainment symptoms. It explains the process of bypassing modules to find the fault.
• PI1149A: Provides diagnostic aid for intermittent blank displays with or without audio, specifically mentioning DTCs U0028/U0029. It helps differentiate between a MOST bus down condition (blank screen, no audio) and other display issues.
• PIT5405C: Mentions U0028 in a long list of DTCs that can be set due to various electrical issues, often related to communication network problems.

Platform-Specific Known Issues

• A pinched dash harness under the driver's side instrument panel is a well-documented issue for 2014-2018 models, covered by multiple revisions of TSB PIT5288. This can cause U0028 along with a wide array of other seemingly unrelated electrical problems.
• A YouTube video by 'Automotive Diagnostics & Programming' titled 'GM M.O.S.T. Bus Testing Made Simple!' demonstrates diagnosing a similar issue on a Buick, showing how scan tool data can point to the specific module that is breaking the ring.
• A repair story on iATN details a 2015 Silverado with U0028 where the technician used scan data to identify the CD player as the faulty node, then bypassed it to confirm the diagnosis and restore radio function.

Mechanic-Grade Diagnostic Values

• MOST Bus Light Signal — expected: A visible red light should be present at the output port of a functioning module's fiber optic cable when the system is active.. Failure: No red light coming from a module's output port indicates a break in the ring. The module before the break (the one not sending light) is likely the cause.
• GDS2 Scan Tool - 'Number of MOST Communication Breaks' — expected: 0. Failure: A value of 1 or more indicates a complete break in the MOST ring. If U0029 is also present, this value may be 0, indicating the ring is intact but a module is malfunctioning.
• GDS2 Scan Tool - 'Surrogate MOST Master Node Upstream Position' — expected: N/A. Failure: If a number (e.g., 2) is displayed, it indicates which module is reporting the communication failure. Counting backwards from the last module in the ring (IPC) by that number points to the suspect module. For example, a value of 2 points to the CD player.

Hidden / Shadow Codes Worth Checking

• U0028 sym00: This is the standard code with a symptom byte of '00', indicating a general MOST bus fault. GM's diagnostic tool, GDS2, displays these symptom bytes which can provide more specific diagnostic direction. (see via GM GDS2 or a high-end professional scan tool.)

Scan Tool Commands That Help

• GDS2 (Global Diagnostic System 2): Vehicle DTC Information / Module Scan — This is the initial step to see which modules are reporting codes and which are not communicating at all. It can identify U0028, U0029, and other related communication faults.
• GDS2 (Global Diagnostic System 2): Radio Data > MOST Data — After finding U0028, this screen provides specific data like 'Number of MOST Communication Breaks' and 'Surrogate MOST Master Node Upstream Position' to help pinpoint the location of the fault in the ring.
• SPS (Service Programming System): HMI Control Module Programming and Setup — This function is required after replacing the HMI module. It programs the new module with the vehicle's VIN and specific configuration, without which the infotainment system will not work.

Wiring & Ground Locations

• 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. A poor connection here, often caused by trapped insulation, can lead to a host of intermittent electrical problems, including network communication codes like U0028.
• Left I/P Dash Mounting Bracket — Under the driver's side dash, near the parking brake pedal assembly.. This is the location of the well-documented pinched harness issue described in TSB PIT5288H. The main dash harness can be chafed or crushed by this metal bracket, causing shorts or opens in the MOST bus circuits.
• HMI Module — Behind the upper and lower glove box compartments on the passenger side of the dashboard.. This is the physical location of the Human Machine Interface module, a primary node on the MOST bus. Access is required for bypass testing or replacement.

Real Owner Repair Stories

• iATN (International Automotive Technicians Network) Case Study (2015 Chevrolet Silverado) — MyLink display was dark, radio would not play, and all control buttons were non-functional.
  ❌ Tried (didn't work) Initial thought was a wiring/connection problem, but the presence of code U0029 alongside U0028 suggested the MOST ring still had integrity.
  ✅ What actually fixed it Using GDS2 scan tool data, the 'Surrogate MOST Master Node Upstream Position' was '2'. Counting back two nodes from the end of the ring (IPC -> HMI) pointed to the CD player. The technician could not communicate with the CD player. The CD player was removed, the data lines on its connector were jumped (bypassed), and all infotainment functions were restored. The faulty CD player was the cause.

OEM Part Supersession History

• Varies by year and options → Varies, GM frequently updates part numbers — Hardware revisions, software updates, and component changes.
  Heads up: When replacing an HMI module, you must use one intended for the same model year and RPO code (IO5 for non-navigation, IO6 for navigation). Using an incorrect module can lead to function loss or complete incompatibility, even if it physically fits. Third-party sellers often program used modules to a specific VIN to ensure compatibility.

Model Year Variations Within This Range

• 2013-2018: The infotainment system is identified by RPO codes, typically found on a sticker in the glove box. IO5 indicates the 8-inch screen without factory navigation, while IO6 indicates the 8-inch screen with factory navigation. These systems use different HMI modules and software. Upgrading from IO5 to IO6 is possible but requires the correct HMI module, a GPS antenna splitter, and specific programming.
• 2014-2018 (K2XX Platform): These model years are specifically called out in TSB PIT5288H regarding the pinched wiring harness near the left I/P mounting bracket. While a wiring issue can happen on any vehicle, this specific failure pattern is a known defect on this platform.