U0073 on 2017-2019 GMC Sierra 3500: Causes and Fixes for Communication Bus Failure

What's Unique About the 2017-2019 Gmc SIERRA 3500

For this generation of GM heavy-duty trucks (K2XX platform), the Serial Data Gateway Module (SDGM) is a focal point for communication issues. Manufacturer TSBs #PIT5586B and #PIT5586C specifically instruct dealers to investigate the SDGM when a U0073 code appears alongside other communication faults. This suggests the module itself, or its associated X1 and X2 connectors, are common points of failure. Another extremely common issue on this platform is a poor G218 ground connection under the driver's dash, often caused by sound-deadening material being trapped under the ground lug from the factory.

Diagnostic Flowchart

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

Symptoms You May Notice

• Multiple warning lights on the dashboard (Check Engine, ABS, Stabilitrak, Service Airbag)
• HVAC controls are inoperative [PIT5586B, PIT5586C]
• Instrument cluster gauges drop to zero or behave erratically
• Loss of turn signal sounds or other chimes
• Engine may not start or could stall while driving
• Transmission may shift harshly or go into limp mode
• Loss of power features like door locks or interior lights
• Radio display is blank
• Steering Wheel Controls (SWC) not illuminated

Most Likely Causes

1. Poor Ground Connection (G218) 🔴 High Probability GM trucks of this era are known for issues with the G218 ground under the driver's side dash. From the factory, sound-deadening insulation material often gets trapped between the ground lug and the metal chassis, creating a poor, intermittent connection that wreaks havoc on the network.
   How to confirm: Locate the G218 ground stud under the driver's side dash, usually bolted to the A-pillar frame behind the kick panel. Disassemble the connection and check for the presence of black foam or matting under the metal eyelet. A voltage drop test can also confirm a bad ground.
   Typical fix: Remove the ground nut and terminal(s). Cut away the interfering section of the insulation mat. Clean the terminal eyelet and the chassis stud to bare metal with a wire brush or sandpaper. Reassemble securely.
   Est. part cost: $0-$5
2. Faulty Serial Data Gateway Module (SDGM) or Connectors 🔴 High Probability TSBs #PIT5586B and #PIT5586C specifically point to the SDGM as a primary cause. The module can suffer from an internal 'logic lock' (requiring a reset) or physical connection issues at its X1 and X2 connectors, such as bent, loose, or backed-out pins.
   How to confirm: As a diagnostic step, locate the SDGM fuse (often F26DL for trucks, F28DL for SUVs) and pull it for one minute, then reinstall. If communication returns, a logic lock was the issue. If not, inspect the X1 (gray) and X2 (black) connectors at the SDGM for any visible damage, corrosion, or loose terminals.
   Typical fix: For logic lock, the reset may be a temporary fix until a software update is available. For physical issues, repair the affected terminal or replace the connector pigtail. 🎬 See how to install an SDGM bypass harness for troubleshooting. If the module itself is faulty, it must be replaced and programmed by a dealer or qualified shop.
   Est. part cost: $150-$350
3. Wiring or Connector Issues 🟡 Medium Probability Harnesses can rub against sharp metal brackets, especially around the parking brake pedal assembly, under the driver's door sill plate, and at the firewall pass-through.
   How to confirm: Visually inspect wiring harnesses for chafing, especially in known problem areas. Check major connectors (like X225 behind the instrument panel) for backed-out pins, corrosion, or looseness.
   Typical fix: Repair the damaged section of wire using solder and heat-shrink tubing. Re-seat or replace damaged connectors or terminals. Protect the harness with anti-chafe tape or loom to prevent future damage.
   Est. part cost: $10-$50
4. Weak or Failing Battery / Alternator ⚪ Low Probability Modern control modules are sensitive to voltage. A battery that drops below 12.0V during startup or an alternator with fluctuating output can cause modules to fail their initialization and drop off the network, triggering a U0073.
   How to confirm: Test the battery voltage with the engine off (should be >12.4V). Perform a load test. Check the alternator output with the engine running (should be stable between 13.7-14.7V).
   Typical fix: Replace the weak battery or faulty alternator.
   Est. part cost: $150-$500

Rare But Worth Checking

• Blown 175-Amp Mega Fuse After Jump Start: If the U0073 code appeared immediately after a jump start (especially if cables were reversed), check the 175-Amp mega fuse. It's located in the battery distribution block, a small box on or near the positive battery terminal. A voltage spike can blow this fuse to protect the vehicle's computers, shutting down the network. It must be tested with a multimeter for continuity as it can be broken internally without visible signs. An example part is a Littelfuse 0298175.
🎬 Watch: How to find and replace a blown mega fuse.
• Faulty Aftermarket Electronics: Improperly installed remote starters, alarms, aftermarket lighting, or trailer brake controllers can tap into CAN bus wires incorrectly, causing interference or shorts that bring down the network.
• Failed Terminating Resistor: The CAN bus requires two 120-ohm resistors. One is internal to the ECM. The second is an external resistor located in the wiring harness at the rear of the vehicle, often taped to the harness above the spare tire. If this resistor or its wiring fails, the total network resistance will read 120 ohms instead of the correct 60 ohms, causing communication failure.

Diagnosis Steps

1. Check Battery and Charging System: Ensure the battery is fully charged (>12.4V) and passes a load test. Verify alternator output is stable between 13.7-14.7V when running.
2. Scan All Vehicle Modules: Use a professional scan tool to identify which modules are not communicating. A long list of 'U' codes points to a network-wide failure.
3. Inspect and Clean Ground G218: Locate the G218 ground stud under the driver's side dash/kick panel. Disassemble, check for and remove any trapped insulation mat, clean all surfaces to bare metal 🎬 Watch: Step-by-step guide to fixing the G218 ground connection., and re-tighten securely. This is the highest probability fix.
4. Reset the SDGM: Locate the fuse for the Serial Data Gateway Module (often F26DL). Pull the fuse for 60 seconds and reinstall it. If communication is restored, the module had a 'logic lock'.
5. Inspect SDGM Connectors: If the reset fails, locate the SDGM under the driver's side dash. Disconnect its X1 and X2 connectors and inspect for bent pins, backed-out terminals, or corrosion as per GM bulletin PIT5586C.
6. Measure CAN Bus Resistance: With the battery disconnected, use a multimeter to measure resistance between Pin 6 (CAN High) and Pin 14 (CAN Low) at the OBD-II port. A healthy network should read approximately 60 ohms. A reading of 120 ohms indicates an open circuit or a missing terminating resistor. A reading near 0 ohms indicates a short circuit between the two CAN wires.
7. Isolate the Fault: If resistance is incorrect, begin disconnecting modules one by one from the CAN bus (starting with the TBCM, ABS module, etc.), re-measuring resistance each time. When the resistance returns to 60 ohms, the last module disconnected (or the wiring to it) is likely the source of the fault.

Parts You'll Likely Need

• Serial Data Gateway Module (SDGM) (OEM #84548114) — This module is a known failure point according to manufacturer TSBs, prone to both internal logic locks and connector issues. It acts as the central router for network communications. [PIT5586B, PIT5586C]
  Trusted brands: ACDelco (Genuine GM)
  OEM price range: $150-$350
  Aftermarket price range: $100-$200
• 175A Mega Fuse — This large fuse on the battery distribution block can blow during a jump start with a voltage spike, shutting down the entire network to protect control modules.
  Trusted brands: Littelfuse 0298175
  OEM price range: $10-$20
  Aftermarket price range: $5-$15
• CAN Bus Terminating Resistor — The external 120-ohm resistor, typically located in the rear harness, can fail or its wiring can break, which will take down the network.
  Trusted brands: ACDelco, Dorman
  OEM price range: $15-$30
  Aftermarket price range: $10-$20

Related Codes That Often Appear With This One

• U0100 — Lost Communication With ECM/PCM
• U0101 — Lost Communication with TCM
• U0121 — Lost Communication With Anti-Lock Brake System (ABS) Control Module
• U0140 — Lost Communication With Body Control Module
• U0155 — Lost Communication With Instrument Panel Cluster (IPC) Control Module

Technical Service Bulletins (TSBs) & Recalls

• PIT5586B: HVAC controls inoperative, multiple DTCs set, instructs to check Serial Data Gateway Module.
• PIT5586C: Updated version of PIT5586B with similar instructions.
• N212353390: Service update for reprogramming the SDGM on certain GM vehicles if it was replaced in service, as it may not have been programmed correctly.

Platform-Specific Known Issues

• TSB #PIT5586C: This bulletin directly addresses a situation where multiple communication codes, including U0073, are stored. It instructs technicians to inspect the Serial Data Gateway Module (SDGM) X1 and X2 connector terminals for being bent, backed out, or having loose tension.
• TSB #PIT5405C: While for a slightly older generation, this TSB is relevant as it established the G218 ground as a known problem area for GM trucks, specifically citing an insulator mat getting trapped under the ground terminal and causing intermittent communication issues.
• SDGM 'Logic Lock' (per GM Document 5400230): GM has acknowledged a software anomaly in the SDGM that can cause it to stop communicating. The initial fix is to perform a reset by pulling the module's fuse for one minute. A software update was planned to permanently fix this.

Mechanic-Grade Diagnostic Values

• CAN Bus Resistance — expected: ~60 Ohms. Failure: A reading of ~120 Ohms indicates an open circuit or a missing terminating resistor. A reading near 0 Ohms indicates a short between the CAN High and Low wires.
• CAN Bus Voltage (Recessive State) — expected: ~2.5V on both CAN High and CAN Low. Failure: Significant deviation from 2.5V on either line suggests a potential short to power or ground.
• CAN Bus Voltage (Dominant State) — expected: CAN High: ~3.5V, CAN Low: ~1.5V. Failure: Inability for the lines to be pulled to these respective voltages during communication indicates a bus problem.
• System Voltage — expected: >12.4V (engine off), 13.7V - 14.7V (engine running). Failure: Low static voltage or fluctuating/improper charging voltage can cause modules to randomly drop off the network.

Scan Tool Commands That Help

• GM GDS2 (or equivalent professional scanner): Module Status / Network Test — This is the first step to get an overview of the entire vehicle network. It will show a list of all expected control modules and which ones are currently 'Not Communicating'. A long list of non-communicating modules confirms a network-wide U0073 fault rather than a single module failure.
• GM GDS2: SDGM Programming/Setup — This function is required after replacing the Serial Data Gateway Module. The new module must be programmed with the vehicle's specific configuration and VIN to function correctly on the network.

Wiring & Ground Locations

• G218 — Under the driver's side dash, bolted to the A-pillar frame, usually behind the kick panel.. This is a primary ground point for multiple modules, including the BCM. A poor connection here, often due to trapped insulation from the factory, is a top cause of intermittent network failure and U0073.
• CAN Bus Terminating Resistor (External) — Taped to the main wiring harness, located above the spare tire in the rear of the vehicle.. The CAN bus requires two 120-ohm resistors for proper operation. One is in the ECM, and this is the second. If this resistor or its wiring is damaged, the total network resistance will be 120 ohms instead of 60, causing communication failures.
• SDGM (Serial Data Gateway Module) — High in the driver's footwell, typically to the left of the steering column and above the brake pedal.. This is the central hub or router for the CAN network. TSBs point to it as a primary failure point, either through internal logic lock or issues with its X1 and X2 connectors.
• OBD-II DLC (Data Link Connector) — Under the driver's side dashboard.. Pin 6 (CAN High) and Pin 14 (CAN Low) are the direct access points for testing the entire high-speed network's resistance and voltage.

Real Owner Repair Stories

• Multiple forum users and YouTube videos for 2014-2018 GM Trucks (2017-2019 GMC Sierra / Chevy Silverado) — Flickering dash lights, loss of power steering, multiple warning lights, truck shutting off, radio and HVAC blank.
  ❌ Tried (didn't work) Replacing the battery, Replacing the alternator, Clearing codes (they returned immediately)
  ✅ What actually fixed it Locating ground G218 under the driver's side dash, finding the foam sound-deadening mat trapped under the ground lug, cutting the mat away, cleaning the metal contacts, and re-securing the ground nut.
• YouTube diagnostic video for GM Trucks (GMC Sierra / Chevy Silverado) — No start, limp mode, U0073 and a flood of other communication codes immediately after receiving a jump start.
  ❌ Tried (didn't work) Clearing codes, Checking individual module fuses
  ✅ What actually fixed it Replacing the 175-amp mega fuse located on the battery distribution block. The fuse had blown from the voltage spike during the jump start, protecting the modules but taking the network offline. A 'Global Power Reset' (disconnecting battery cables and touching them together for 60 seconds) was also performed after replacement to clear module logic locks.

"I Checked Everything" — The Actual Cause

• A technician may find that the CAN bus resistance measures a perfect 60 ohms at the OBD-II port, and all visible wiring appears intact, yet the U0073 code persists. The actual cause is often an internal 'logic lock' within the Serial Data Gateway Module (SDGM). This is a software/firmware glitch, not a physical wiring fault. It can frequently be resolved by a hard reset (disconnecting the battery for several minutes) or by pulling the specific fuse for the SDGM (F26DL) to force it to reboot.

OEM Part Supersession History

• 13599318 → 84548114 — This is a common supersession for the Serial Data Gateway Module (SDGM) in this era of GM trucks and SUVs. The newer part number likely contains updated hardware or firmware to address reliability issues like the 'logic lock' condition.