U3023 on 2020-2024 GMC Sierra 3500: Network Power Fault, Stall, and No-Start Fixes

What's Unique About the 2020-2024 Gmc SIERRA 3500

The 2020-2024 Sierra HD and Silverado HD platforms, particularly models with the 6.6L L5P Duramax engine, have a specific issue documented by General Motors. TSB #24-NA-124 directly links U3023 to a constellation of other trouble codes and severe symptoms like stalling or a no-start condition. Furthermore, the L5P engine bay is known for wiring harness vulnerabilities where vibration and tight packaging can lead to chafing against components like the steering shaft 🎬 Watch: See exactly where the L5P harness rubs and chafes. or valve covers, causing high resistance or shorts over time. This indicates a known pattern of failure in a specific wiring harness or power distribution point, rather than a random component failure.

Diagnostic Flowchart

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

Symptoms You May Notice

• Engine will not start
• Engine stalls while driving
• Crank but no start condition
• Check Engine Light is on
• Multiple warning messages on the instrument cluster (e.g., 'Service Transmission', 'Service 4WD System')
• Loss of power to various electronic accessories
• In some cases, the truck may start and run perfectly fine after an intermittent no-start event.

Most Likely Causes

1. Wiring Harness or Connector Fault (per TSB #24-NA-124) 🔴 High Probability GM has identified a specific electrical issue on these trucks, particularly diesel models, that causes this exact cluster of codes. The L5P platform has known wiring vulnerabilities where harnesses can chafe against engine or frame components, and connectors can develop high resistance from engine vibration. A Reddit user with a 2024 Silverado confirmed their identical issue was resolved by fixing a 'loose wire.'
   How to confirm: A technician must follow the diagnostic procedure outlined in TSB #24-NA-124, which involves inspecting specific wiring harnesses (such as the X204 connector, 🎬 Watch: Locate every critical connector on your Duramax engine. among others), connectors, and ground points for damage, corrosion, or poor connections. A thorough visual inspection of harnesses for chafing is critical. 🎬 See a real-world example of this major electrical failure.
   Typical fix: Repairing the damaged section of the wiring harness or replacing the faulty connector with a pigtail kit. This is a labor-intensive job that requires precision.
   Est. part cost: $20-$150
2. Blown Fuse or Faulty Power Distribution Center 🟡 Medium Probability Modern trucks have multiple fuse boxes and power distribution centers. A single fuse can protect the power feed to multiple modules, and its failure would trigger this type of widespread communication loss.
   How to confirm: Visually inspect all fuses in the engine bay and interior fuse panels. Use a multimeter to test fuses that supply power to the ECM, TCM, and BCM, particularly those related to ignition power circuits.
   Typical fix: Replace the blown fuse. If the fuse blows again, it indicates a short circuit in the wiring that must be traced.
   Est. part cost: $1-$10
3. Faulty Ignition Switch ⚪ Low Probability → Shop Ignition Switch
   How to confirm: Test the voltage at the output terminals of the ignition switch in the 'RUN' and 'START' positions. If the voltage is below the manufacturer's specification (typically below 12V), the switch is likely faulty.
   Typical fix: Replace the ignition switch.
   Est. part cost: $50-$150

Rare But Worth Checking

• Failed Engine Control Module (ECM): → Shop Engine Control Module (ECM) While less common than wiring issues, a Reddit user with a 2024 Sierra HD Duramax reported a crank-no-start condition that was resolved by replacing the ECM. The dealer's diagnosis was 'low output voltage' from the module itself. This should only be considered after all wiring and power supply issues have been ruled out.

Diagnosis Steps

1. Connect a professional scan tool capable of reading all vehicle modules, not just the ECM. Document all present DTCs, paying close attention to the cluster of U3023, P2534, and P0700.
2. Check the battery state of charge and perform a load test to ensure it is healthy.
3. Visually inspect and test all fuses in the engine bay and interior fuse panels, especially those related to the ECM, TCM, and BCM ignition circuits.
4. Obtain and follow the diagnostic procedure for TSB #24-NA-124. This will guide the inspection of specific known-problem areas in the wiring harness and connectors.
5. Perform a thorough visual inspection of major wiring harnesses in the engine bay. Pay close attention to harness routing and any points of contact with the engine block, frame, or steering components, looking for signs of chafing or abrasion.
6. If the TSB does not resolve the issue, use a wiring diagram and a digital multimeter to test for proper voltage and ground at the primary connectors for the ECM and TCM.
7. Test the ignition switch circuit for proper voltage output in the 'RUN' and 'START' positions.
8. If all wiring, grounds, and power sources test good, the final step is to suspect a faulty control module, likely the ECM, as reported in some owner experiences.

Parts You'll Likely Need

• Wiring Harness Repair Kit / Pigtail Connector (OEM #e.g., ACDelco 19300397 (example)) — The most probable cause, according to GM's TSB and owner reports, is a fault in the wiring or a connector, which often requires a repair kit rather than a full harness replacement.
  Trusted brands: ACDelco, Fleece Performance (e.g., FPE-HAR-L5P-INJ for injector harness)
  OEM price range: $40-$150
  Aftermarket price range: $20-$80
• Engine Control Module (ECM) — In rare cases where all wiring and power inputs are confirmed to be good, the ECM itself may have an internal fault causing the power loss or communication issue. This is an expensive last resort.
  Trusted brands: ACDelco
  OEM price range: $800-$1200
  Aftermarket price range: $500-$900

Related Codes That Often Appear With This One

• P2534 — This code means 'Ignition Switch Run/Start Position Circuit Low' and is a direct indicator of the power loss that causes the U3023 network code.
• P0700 — This is a generic fault code from the Transmission Control Module (TCM). It sets when the TCM loses power or detects an internal fault, which is a direct consequence of the issue causing U3023.
• P129D — This is another manufacturer-specific code often related to fuel pump or injector control module performance, which can be triggered by the same power supply issue.
• P10DB — This code is specific to the L5P Diesel engine and is often associated with Reductant Control Module issues, which can also be triggered by a network power fault.

Technical Service Bulletins (TSBs) & Recalls

• 24-NA-124: Malfunction Indicator Lamp Illuminated, Stall, or No Start with DTC P2534, U3023, P0700, P129D, P10DB (w/ L5P Diesel), P103B, P17E0.

Platform-Specific Known Issues

• TSB #24-NA-124 documents a known electrical issue on these trucks, particularly with the L5P diesel engine, that causes a stall or no-start condition accompanied by codes P2534, U3023, P0700, and others.
• Pattern of Wiring Vulnerability: The L5P engine platform has documented issues with wiring harnesses chafing against engine or frame components and connector pins developing high resistance from vibration. While TSB #24-NA-124 points to a specific fault, other issues like injector harness failures (causing code P0204) demonstrate a broader pattern of electrical connector and wiring issues on these trucks.

Mechanic-Grade Diagnostic Values

• Resistance of B+ or Ignition circuit wiring, end-to-end — expected: Less than 2.0 Ω. Failure: A reading of 2.0 Ω or greater indicates high resistance or an open in the circuit that needs repair.
• Resistance between B+ or Ignition circuit and ground — expected: Infinite resistance (OL on most multimeters). Failure: A reading of less than infinite resistance indicates a short to ground in the circuit.
• Alternator output voltage at battery terminals with engine running — expected: Typically 13.5V to 14.5V. Failure: Voltage that is too low or too high can cause issues with control modules.

Scan Tool Commands That Help

• GM GDS2: Vehicle DTC Information — This is the initial step to query all modules on the vehicle's network and display all stored Diagnostic Trouble Codes, which is critical for seeing the full cluster of codes (P2534, P0700, U3023) that points to the specific TSB.
• GM GDS2: Data Bus Diagnostic Tool — This function helps analyze the vehicle's data bus to identify which control modules are not communicating, which is the direct cause of a U-series code like U3023. It can help pinpoint the start of the network break.
• GM GDS2: Control Functions (within a specific module like BCM) — Allows for bidirectional control to test specific outputs (like lights, locks, etc.) to determine if a module is receiving power and is functional, even if it's having intermittent communication issues.

Wiring & Ground Locations

• X115 — Main body-to-engine wiring harness connector, often located on the driver's side of the engine bay.. This is a major pass-through connector for numerous circuits, including power and data lines for the ECM and TCM. A poor connection, corrosion, or damaged pin in this connector can cause a loss of power or communication to multiple modules, triggering the U3023/P2534/P0700 code cluster.
• Engine Block to Frame/Body Grounds — Multiple locations, but a key ground strap is often located on the driver's side, running from the rear of the engine block to the firewall/chassis. Another is located near the front of the vehicle, from the engine block to the frame, often behind a front wheel.. These main ground straps are critical for the entire electrical system. Corrosion or breakage of these straps, a known issue on GM trucks, can cause floating grounds and unpredictable voltage drops, leading to a wide array of electrical DTCs, including network and module power faults.
• ECM/PCM Ground — A specific ground wire for the Powertrain Control Module is often routed in the main engine harness and attached to the top of the engine block.. If this specific ground for the ECM is compromised, the module cannot function correctly and may not power up or communicate, directly leading to codes like U3023.

Real Owner Repair Stories

• Reddit user PriorDry4400 in r/Silverado (2024 Chevrolet Silverado Trail Boss with 3,400 miles) — Check Engine Light on, with codes P2534, P059F, P0700, and U3023. Truck seemed to run perfectly fine.
  ❌ Tried (didn't work) The user took it to an auto parts store for a scan but was on vacation and couldn't immediately go to a dealer.
  ✅ What actually fixed it The dealership found two issues: a 'loose wire' and debris obstructing the active grille shutters (related to code P059F). The loose wire was the cause of the P2534/P0700/U3023 cluster, directly confirming the common cause.

Model Year Variations Within This Range

• 2024+: For the 2024 model year, the Sierra/Silverado HD received a significant interior and technology refresh on LT, LTZ, and High Country trims. This included a new 13.4-inch infotainment screen and a 12.3-inch digital driver information center. These changes introduce different Body Control Modules (BCM) and network architecture compared to the 2020-2023 models, which could potentially alter diagnostic paths for network codes, though the underlying engine and transmission power distribution circuits remain similar.