U0140 on 2014-2021 GMC Sierra 1500: Lost Communication With BCM Fixes

What's Unique About the 2014-2021 Gmc SIERRA 1500

On these modern GMC Sierra trucks, the electrical system is a complex network involving the BCM, ECM, and a Serial Data Gateway Module (SDGM). This complexity means a U0140 code is often not a simple component failure. GM has issued multiple Technical Service Bulletins (TSBs) for this year range indicating that software glitches within the ECM or SDGM can cause a 'logic lock' or communication loss, requiring a dealer-level reprogram. [N192267870, PIT5586G] This is different from older vehicles where a communication code almost always pointed to a wiring fault or a bad module. The SDGM, in particular, can suffer from loose connector terminals, causing widespread network issues. [PIT5586G]

Diagnostic Flowchart

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

Generation note: This range covers two Sierra 1500 generations: the third-gen K2XX (2014-2018) and the fourth-gen T1XX (2019-2021). While causes are similar, TSB #N192267870 specifically calls out an ECM reprogram for 2019 models to fix a combination of U-codes including U0140. The K2XX models are particularly noted in TSBs for issues with the Serial Data Gateway Module (SDGM) connectors. [PIT5586G] The T1XX generation introduced GM's Vehicle Intelligence Platform (VIP), which uses the SDGM more extensively to isolate secure networks, making its function even more critical.

Symptoms You May Notice

• Check Engine Light is on
• Multiple warning messages on the driver information center, such as 'Service Stabilitrak' or 'Service Trailer Brake System'. [PIT5713A]
• Malfunctioning power windows, door locks, or remote keyless entry.
• Erratic or non-functional interior and exterior lights.
• Wipers operating incorrectly or not at all.
• Vehicle may not start or crank.
• Complete loss of power/stalling, sometimes when turning at low speeds.
• Radio or infotainment screen goes blank or freezes.
🎬 Watch: Common symptoms of a failing Body Control Module

Most Likely Causes

1. Wiring or Connection Fault 🔴 High Probability Complex wiring harnesses are susceptible to issues. TSB PIT5586G specifically points to bent, backed out, or loose terminals at the X1 and X2 connectors of the Serial Data Gateway Module (SDGM) on 2017 models. Chafing can also occur near the parking brake mechanism or where harnesses pass through the firewall.
   How to confirm: Visually inspect wiring harnesses connected to the BCM and SDGM. A common trouble spot is the SDGM connectors. [PIT5586G] Check major ground points like G218 (under the driver's side dash). A multimeter can be used to check for continuity and shorts on the CAN bus wires (pins 6 and 14 at the OBD-II port).
   Typical fix: Repairing the damaged section of the wiring harness, cleaning/re-seating connectors at the BCM and SDGM, or repairing ground connections.
   Est. part cost: $10-$100
2. Module Software Glitch / Needs Reprogramming 🔴 High Probability As per GM TSBs, software anomalies can cause communication to drop. TSB #N192267870 specifically instructs dealers to reprogram the ECM on 2019 models. TSB #PIT5586G points to a 'logic lock' of the Serial Data Gateway Module, which can be resolved with a software update. [N192267870, PIT5586G] Owners on forums have reported dealers successfully fixing the issue with a reprogram.
   How to confirm: A dealer or qualified shop must check for available software updates for the ECM, BCM, and SDGM using GM's service software (GDS).
   Typical fix: Reprogramming the affected module(s) with the latest software.
   Est. part cost: $0 (if under warranty) - $200
3. Faulty Body Control Module (BCM) 🟡 Medium Probability → Shop Body Control Module While less common than wiring or software issues, the BCM itself can fail internally due to moisture intrusion, vibration, or age. Water leaks from the windshield or A-pillar are a known cause of BCM failure on this platform.
   How to confirm: After ruling out all wiring, ground, and software issues, the BCM is the likely culprit. A technician may note the BCM is completely 'offline' during a network scan, but this can also be a symptom of a wiring short as described in TSB PIT4730B. Cycling the ignition may restore communication, which strongly points towards a wiring issue rather than a bad module.
   Typical fix: Replacing the BCM. The new module must be programmed to the vehicle's VIN and specific options.
   Est. part cost: $250-$500
4. Low Battery Voltage or Poor Ground 🟡 Medium Probability → Shop Vehicle Battery These trucks are highly sensitive to voltage. A weak battery or a corroded main ground can cause unpredictable communication errors. TSB PIT5405C notes that electrical issues are more likely at low speeds while turning, which increases electrical load. The main BCM ground point (G218) under the driver's side dash is a critical point to check, as the dash insulator mat can get trapped under the ground terminal from the factory, causing a poor connection.
   How to confirm: Test the battery's state of charge and health (must be above 12.4V at rest). Perform a load test. Inspect the main battery and chassis ground connections for tightness and corrosion, especially the ground strap from the engine to the frame and the G218 ground point.
   Typical fix: Replacing a weak battery or cleaning/tightening ground connections. Some owners perform a 'Big 3' ground wire upgrade as preventative maintenance.
   Est. part cost: $5-$250

Rare But Worth Checking

• Aftermarket Accessory Interference:

Diagnosis Steps

1. Scan all vehicle modules for stored trouble codes. Note all 'U' codes and which modules are reporting them. A tool with network topology view is very helpful.
2. Check for Technical Service Bulletins (TSBs) related to U0140 for your specific VIN. Pay close attention to N192267870 (2019 ECM reprogram) and PIT5586G (SDGM connectors).
3. Perform a hard reset by disconnecting the battery terminals for 30 minutes. This can sometimes clear a module 'logic lock' but is not a permanent fix.
4. Inspect the battery and check system voltage. Ensure it's stable and above 12.4 volts. Load test the battery.
5. Locate the BCM (typically under the driver's side dashboard, to the left of the steering column, often integrated with the fuse block) and inspect its connectors for corrosion, moisture, or damage.
6. Inspect all major chassis and engine ground points for tightness and corrosion. Specifically check ground G218 under the driver's side A-pillar trim, ensuring the insulator mat is not trapped under the terminal.
🎬 Watch: How to fix the G218 ground connection issue
7. Per TSB PIT5586G, inspect the X1 and X2 connectors at the Serial Data Gateway Module (SDGM) for any bent, loose, or backed-out terminals. The SDGM is located under the driver's side of the dash, near the BCM.
8. Using a multimeter, check the resistance between pins 6 (CAN High) and 14 (CAN Low) of the OBD-II port (with the battery disconnected). A reading of approximately 60 ohms indicates the CAN bus terminating resistors are intact.
9. If wiring, grounds, and power supply are good, consult a dealer to check for and apply any available software updates to the ECM, BCM, or SDGM.
10. If all other steps fail, the BCM is likely faulty and requires replacement and programming.

Parts You'll Likely Need

• Body Control Module (BCM) (OEM #13594692 (Example for 2014-2015 K2XX models, always verify by VIN)) — If wiring, grounds, and software are confirmed to be good, the internal circuitry of the BCM is the next logical point of failure.
  Trusted brands: ACDelco
  OEM price range: $300-$550
  Aftermarket price range: $200-$400

Related Codes That Often Appear With This One

• U0073 — This code means 'Control Module Communication Bus A Off'. It often appears with U0140 as it indicates a general high-speed network communication failure, which is the root cause of the BCM-specific code. [PIT5677E, PIT5713A, PIT5405C]
• U0100 — Lost Communication with ECM/PCM. This can be set in other modules when the entire network is disrupted by the same fault causing the U0140. [PIT5677E, PIT5713A, PIT5586G]
• U0101 — Lost Communication with TCM (Transmission Control Module). Like U0100, this indicates a wider network problem. [N192267870, PIT5713A, PIT5586G]

Technical Service Bulletins (TSBs) & Recalls

• N192267870: Recommends ECM reprogram for U-code combinations on 2019 models.
• PIT5677E: Lists U0140 as part of a large group of potential electrical system DTCs.
• PIT5713A: Associates U0140 with multiple warning messages on the instrument panel.
• PIT5586G: Points to a possible 'logic lock' or connector terminal issue at the Serial Data Gateway Module.
• PIT5405C: Suggests checking the Body Control Module for a group of communication codes.
• PIT4730B: Details how an intermittent wiring short can mimic a failed BCM.

Platform-Specific Known Issues

• TSB #N192267870: For 2019 models, a combination of U-codes including U0140 can be stored in the ECM. The official fix is to reprogram the ECM.
• TSB #PIT5586G: For 2017 models, specifically calls out checking for loose terminals in the Serial Data Gateway Module (SDGM) connectors.
• TSB #PIT5405C: For 2014 models, highlights a poor BCM ground at G218 where the dash insulator mat can get trapped under the ground terminal, causing a poor connection that is often more noticeable during low-speed turns.

Mechanic-Grade Diagnostic Values

• High-Speed CAN Bus Resistance — expected: ~60 Ohms (with battery disconnected). Failure: A reading of ~120 Ohms indicates one of the two terminating resistors is offline. A reading near 0 Ohms indicates a short between the CAN High and CAN Low wires.
• BCM Ground Circuit Resistance — expected: < 1.0 Ohm. Failure: Resistance greater than 1.0 Ohm between the BCM ground pin at the connector and a clean chassis ground point indicates a poor ground connection, which is a known issue at G218.
• CAN High (Pin 6 at DLC) Voltage — expected: ~2.5V (recessive state) to ~3.5V (dominant state). Failure: Voltage stuck at one level or outside this range indicates a bus problem like a short to power or ground.
• CAN Low (Pin 14 at DLC) Voltage — expected: ~2.5V (recessive state) to ~1.5V (dominant state). Failure: Voltage stuck at one level or outside this range indicates a bus problem. The voltage on CAN Low should be a mirror image of CAN High.

Hidden / Shadow Codes Worth Checking

• U0140 sym00 or U0073 sym71: These are GM-specific symptom codes that may accompany the primary DTC. TSB PIT4730B references these codes and advises against immediately replacing the BCM, instead pointing towards diagnosing an intermittent electrical fault. (see via A GM dealer-level scan tool like GDS2 (Global Diagnostic System 2) is required to view these specific symptom bytes.)

Scan Tool Commands That Help

• GDS2: Bidirectional Controls / Output Controls — To test if the BCM is responsive, a technician can use the scan tool to command BCM-controlled functions (e.g., 'Turn on Dome Light,' 'Lock Doors'). If the BCM executes the command, it proves the module has power, ground, and is capable of functioning, pointing the diagnosis toward a network communication issue rather than a failed BCM.
• GDS2: Setup SDM Primary Key in BCM — This procedure is required after replacing the BCM. It syncs the new BCM with the existing Sensing and Diagnostic Module (SDM, the airbag module) to prevent an airbag warning light from staying on.
• GDS2: Brake Pedal Position Sensor Relearn — After BCM replacement, this recalibration may be necessary to ensure proper operation of the brake lights and traction control system, which rely on input arbitrated by the BCM.

Wiring & Ground Locations

• G218 — Under the driver's side dashboard, behind the A-pillar lower trim panel. It is a ground stud on the body.. This is a primary ground point for the BCM. TSB PIT5405C specifically identifies that sound-deadening insulation can get trapped between the ground lug and the body, causing a high-resistance connection that leads to intermittent communication loss and codes like U0140.
• Serial Data Gateway Module (SDGM) — On 2017+ models, it is located under the driver's side of the dashboard, often near the BCM and steering column.. The SDGM is a central hub for network traffic. TSB PIT5586G points to loose terminals in its connectors as a direct cause of U0140 and other communication codes. It acts as a gatekeeper between different CAN buses.
• BCM Connectors (X1-X7) — The BCM is located under the driver's side dash, to the left of the steering column. It has multiple large connectors, often color-coded (e.g., green, blue, black, brown).. These are the direct power, ground, and data line inputs/outputs for the module. Any corrosion (from water leaks) or poor pin tension in these connectors will sever communication.

Real Owner Repair Stories

• YouTube user comment on a G218 ground fix video (2014-2018 GMC Sierra/Chevy Silverado (specific year not mentioned)) — Unspecified, but the user described it as 'the biggest headache ever' after spending hours searching for a solution to a ground issue.
  ❌ Tried (didn't work) Extensive online research without a clear solution.
  ✅ What actually fixed it Following a video guide to access the G218 ground under the driver's side dash, pulling back the foam insulation, and tightening the ground nut. The entire process took about 30 minutes and completely fixed the truck.

OEM Part Supersession History

• 13580690 → 13594692 — GM regularly updates service parts to integrate new materials, technologies, or fix previously identified issues.
  Heads up: Part 13594692 is listed as a replacement for 13580690 and fits many 2014-2015 GM trucks and SUVs. However, it is critical to verify the correct part number by VIN, as programming and options can vary significantly. Using a service that clones the original BCM data to the replacement can avoid dealer programming.

Model Year Variations Within This Range

• 2019-2021 (T1XX Platform): These models use GM's Vehicle Intelligence Platform (VIP), which relies more heavily on the Serial Data Gateway Module (SDGM) for network security and routing between CAN and Ethernet buses. A U0140 code on these trucks has a higher probability of being related to an SDGM software or hardware issue, as highlighted by TSB #N192267870 which calls for an ECM reprogram on 2019 models. [N192267870]
• 2014-2018 (K2XX Platform): While still complex, the network architecture is less reliant on the SDGM as a security firewall compared to the later VIP architecture. Issues on these trucks are very commonly traced back to physical wiring faults, particularly the G218 ground point flaw where insulation gets trapped under the terminal from the factory.