U0140 on 2015-2020 Chevrolet Suburban: Causes and Fixes for Lost BCM Communication

What's Unique About the 2015-2020 Chevrolet SUBURBAN

The 2015-2020 Suburban (K2XX platform) uses a complex network architecture with a separate Serial Data Gateway Module (SDGM) to route communications between different vehicle networks. The SDGM is a small box located under the driver's side dash, often near the BCM. Manufacturer TSBs for this specific platform repeatedly point to physical connection failures—specifically the BCM's main ground G218 (located behind the driver's side A-pillar kick panel) and the SDGM's X2 connector—as the primary cause of this code, rather than outright failure of the BCM itself. This makes checking these specific, documented connection points a critical first step.

Diagnostic Flowchart

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

Symptoms You May Notice

• Instrument panel cluster gauges go to zero or the display goes blank.
• Radio and HVAC control displays go blank.
• Multiple warning lights appear on the dash, such as for ABS, traction control, 'Service Stabilitrak', or security.
• Power windows, power door locks, and interior lighting do not work.
• Turn signals may not make a clicking sound or the indicator on the dash won't flash.
• Vehicle may not start or may crank but not start due to the anti-theft system being controlled by the BCM.
• Wipers may behave erratically or park in the wrong position.

Most Likely Causes

1. Poor Body Control Module (BCM) Ground Connection at G218 🔴 High Probability This is a widely documented issue in GM TSB #PIT5405C. The factory assembly process could trap the dash insulator mat between the ground eyelet and the body stud, creating a high-resistance connection over time. This specific ground point is known as G218.
   How to confirm: Locate ground G218 behind the driver's side kick panel, near the A-pillar. Visually inspect if the dash insulation is pinched under the ground terminal. Perform a voltage drop test on the ground circuit; it should be less than 0.1-0.2 volts. Wiggling the ground wire may cause symptoms to appear or disappear.
   Typical fix: Remove the ground nut and eyelet. Cut away any interfering insulation mat. Clean the ground point, stud, and terminal of all corrosion and paint, then securely re-fasten it to bare metal. 🎬 Watch this guide on upgrading your K2XX ground connections.
   Est. part cost: $0-$10
2. Faulty Serial Data Gateway Module (SDGM) Connector 🔴 High Probability GM TSBs #PIT5586B and #PIT5586G specifically call out checking the SDGM's X1 and X2 connectors for terminal issues on these vehicles. Fretting corrosion, backed-out pins, or poor terminal tension are common.
   How to confirm: Locate the SDGM under the driver's dash. Disconnect the battery. Unplug the X1 (black) and X2 (gray) connectors and inspect for any backed-out pins, corrosion, or signs of a poor connection. Wiggle the connectors with the vehicle on (if safe) to see if symptoms change.
   Typical fix: Repair or replace the affected terminals in the connector using the correct terminal release tools. Apply dielectric grease to the connector pins before reassembly to prevent future corrosion. In some cases, a connector pigtail may be needed.
   Est. part cost: $15-$50
3. Blown Fuse for the BCM 🟡 Medium Probability
   How to confirm: Check all fuses related to the BCM in the interior and under-hood fuse panels. A user on a forum noted replacing a 20-amp LTR fuse restored some function. 🎬 See this video to locate your BCM fuses and relays.
   Typical fix: Replace the blown fuse. If it blows again, a short circuit in one of the BCM's power supply wires must be diagnosed.
   Est. part cost: $1-$5
4. Damaged CAN Bus Wiring 🟡 Medium Probability Wiring can be damaged from chafing against sharp metal edges, previous repairs, or aftermarket accessory installation. A forum member found a wiring harness had rubbed through on the frame near the ECM, causing multiple communication codes.
   How to confirm: Visually inspect wiring harnesses connected to the BCM and SDGM. Check for continuity and shorts on the CAN bus high and low circuits using a multimeter. The resistance between the CAN High and CAN Low wires should be approximately 60 ohms with the battery disconnected.
   Typical fix: Repair the broken or shorted section of wire with solder and heat shrink.
   Est. part cost: $5-$25
5. Failed Body Control Module (BCM) ⚪ Low Probability
   How to confirm: This should only be suspected after all power, ground, and network wiring have been confirmed to be good. A professional scan tool will show the BCM as completely unresponsive.
   Typical fix: Replace the BCM. The new module will require programming to the vehicle's VIN and specific options.
   Est. part cost: $250-$450

Rare But Worth Checking

• Failed Serial Data Gateway Module (SDGM): While connector issues are more common, the module itself can fail or enter a 'logic lock' state. If the BCM is communicating but other networks are not, the SDGM could be the cause. A reprogram or replacement may be necessary.
• Low Battery Voltage: Weak or failing batteries can cause unpredictable communication errors between modules. Always ensure the battery is fully charged and passes a load test before diagnosing network faults.

Diagnosis Steps

1. Verify battery voltage is above 12.4V and the charging system is working correctly. Load test the battery, as a weak battery with a bad cell is a known cause of these issues.
2. Scan all vehicle modules with a professional-grade scan tool. Note all 'U' (communication) codes and which modules are not responding.
3. Following TSB #PIT5405C, locate and inspect ground G218. It is behind the driver-side kick panel near the A-pillar. Remove the nut, check for trapped insulation, clean the contact surfaces to bare metal, and tighten securely.
4. Following TSB #PIT5586G, locate the Serial Data Gateway Module (SDGM) under the driver's side dash. Disconnect the battery, then unplug and inspect its connectors (especially the gray X2 connector) for loose pins, corrosion, or damage.
5. Check all fuses related to the BCM in both the interior and under-hood fuse boxes.
6. If connections and fuses are good, use a scan tool to attempt to communicate directly with the BCM. If there is no response, verify all power and ground circuits at the BCM's connectors using a multimeter and wiring diagram.
7. If the BCM has proper power and ground but still does not communicate, the BCM is the most likely cause and requires replacement and programming.
🎬 Watch a breakdown of U0140 causes and potential fixes.

Parts You'll Likely Need

• Body Control Module (BCM) (OEM #13594764, 13506935, 13587704 (multiple exist, verify by VIN)) — This is the part to replace if all wiring, grounds (G218), and fuses are confirmed to be good, but communication is still lost. It requires programming after installation.
  Trusted brands: ACDelco, Dorman
  OEM price range: $300-$450
  Aftermarket price range: $200-$350
• Serial Data Gateway Module (SDGM) (OEM #13534928) — If the BCM is communicating but other networks are not, or if TSB #PIT5586G diagnostics point to it, the SDGM may have failed. It acts as the central router for network traffic. This part also requires programming.
  Trusted brands: ACDelco (GM Genuine Parts)
  OEM price range: $100-$175
  Aftermarket price range: $70-$120

Related Codes That Often Appear With This One

• U0100 — Lost Communication with ECM/PCM. This and other U-codes often appear with U0140 because a BCM or SDGM failure disrupts the entire vehicle network, causing multiple modules to lose communication simultaneously. (See TSB #PIT5586G)
• U0101 — Lost Communication with TCM. Similar to U0100, a network-wide failure will affect communication with the Transmission Control Module. (See TSB #PIT5405C)
• U0155 — Lost Communication With Instrument Panel Cluster (IPC) Control Module. The IPC is often the first place a driver notices a problem. This code is common when the BCM or SDGM fails. (See TSB #PIT5586G)
• U0073 — Control Module Communication Bus 'A' Off. This is a general network fault code that points to a problem with the main CAN bus, often triggered by the same root cause as U0140. (See TSB #PIT5405C)

Technical Service Bulletins (TSBs) & Recalls

• This bulletin directly addresses a wide range of electrical issues, including blank instrument clusters, multiple warning lights, and a list of 'U' codes including U0140. It instructs technicians to inspect the BCM ground G218, located on the driver's side A-pillar, for a poor connection caused by an insulator mat being trapped under the ground eyelet.
• This bulletin addresses symptoms like a no-crank/no-start condition, fluctuating gauges, and a host of communication DTCs, including U0140. It directs technicians to inspect the X1 and X2 connectors at the Serial Data Gateway Module (SDGM) for bent, backed-out, or loose terminals. It also mentions that the SDGM can enter a 'logic lock' state, which may be resolved by a battery disconnect or reprogramming.

Platform-Specific Known Issues

• TSB #PIT5405C identifies a poor BCM ground connection at G218 as a primary cause for multiple communication codes, including U0140. The fix involves removing trapped dash insulation from under the ground terminal.
• TSB #PIT5586G points technicians directly to check the Serial Data Gateway Module (SDGM) connectors for terminal issues or a 'logic lock' state as a cause for a host of U-codes, including U0140.

Mechanic-Grade Diagnostic Values

• CAN Bus Network Resistance — expected: Approximately 60 Ω (Ohms) when measured between Pin 6 (CAN High) and Pin 14 (CAN Low) at the DLC with the battery disconnected.. Failure: A reading of 120 Ω indicates an open circuit or one of the terminating resistors is offline. A reading significantly less than 60 Ω suggests a short between the wires or an extra terminating resistor on the network.
• BCM Ground Circuit Resistance — expected: < 0.1 Ω (Ohms) from the BCM ground pin at the connector to a clean chassis ground.. Failure: A reading higher than 0.1-0.2 Ω indicates high resistance in the ground circuit, often due to the known G218 issue.
• CAN Bus Voltage (Key On, Engine Off) — expected: CAN High (Pin 6 to Ground): ~2.5V to 3.0V. CAN Low (Pin 14 to Ground): ~2.5V to 2.0V.. Failure: Voltages that are significantly off, such as one line being pulled up to 4.5V or higher, often indicate a module on the network has a short or a bad ground, corrupting the data line.

Hidden / Shadow Codes Worth Checking

• U0140 sym00 or U0073 sym71: These manufacturer-specific symptom codes indicate the BCM appears offline on the High-Speed GM LAN. It is triggered when the data circuits experience an intermittent short to ground or to each other multiple times in less than a second. (see via A professional GM-specific scan tool, such as GDS2 (Global Diagnostic System 2).)

Scan Tool Commands That Help

• GDS2 (Global Diagnostic System 2): Module Diagnostics / Vehicle DTC Information — This is the first step to see a list of all modules on the vehicle's networks and which ones are reporting 'No Communication' or have stored DTCs.
• GDS2 (Global Diagnostic System 2): BCM > Control Functions — Used to individually command BCM-controlled outputs (e.g., headlights, wipers, door locks). If the BCM responds to these commands, it proves the module itself is powered, grounded, and functional, shifting the diagnosis towards the network wiring between modules.
• Data Bus Diagnostic Tool: Detected State Test — This function, mentioned in GM TSBs, actively polls the network and provides a list of all modules that are currently communicating. By comparing this live list to a vehicle schematic, a technician can quickly identify which specific modules are offline.

Wiring & Ground Locations

• G218 — Behind the driver's side kick panel, near the A-pillar. It is a ground stud on the body.. This is the primary ground for the Body Control Module. TSB #PIT5405C identifies that the dash insulator mat frequently gets trapped under this ground, causing high resistance and a host of communication issues, including U0140.
• High-Speed CAN Bus Terminating Resistor (Rear) — Underneath the truck near the spare tire area, typically taped to a wiring harness above the muffler.. The CAN bus requires two 120-ohm terminating resistors to function. One is in the ECM, and this is the other. If there is a break in the wiring leading to this resistor, the total bus resistance will read 120 ohms instead of 60, confirming an open circuit. Knowing its location is key to diagnosing this type of fault.
• SDGM Connectors X1 and X2 — The Serial Data Gateway Module is located under the driver's side of the dashboard. X1 is typically black, and X2 is gray.. TSB #PIT5586G specifically instructs technicians to check these connectors for backed-out pins or fretting corrosion. The SDGM is the central router for all network traffic, and a poor connection here can isolate the BCM from other modules.

Real Owner Repair Stories

• YouTube comment on a G218 repair video (2014-2018 GM Truck (same platform and issue)) — Unspecified electrical issues related to a bad ground, leading to hours of online research.
  ❌ Tried (didn't work) Hours of Google searching for a solution.
  ✅ What actually fixed it Following the video's instructions to access ground G218 behind the driver's kick panel, clear the interfering foam insulation, and clean/tighten the ground connection. The owner reported the fix took 30 minutes and solved their 'biggest headache'.
• Auto Repair Tips YouTube Channel (2008 Chevy Cobalt (different vehicle, but identical CAN bus diagnostic principle for U0140/U0101)) — Power steering warning, U0101 (Lost Comm with TCM) and U0140 codes present.
  ❌ Tried (didn't work) Initial scan pointed towards a bad Transmission Control Module (TCM) because unplugging it seemed to stabilize CAN bus voltages.
  ✅ What actually fixed it The mechanic noticed the CAN Low voltage was abnormally high (4.4V instead of ~2.3V). Upon physical inspection of the TCM, he discovered a missing ground wire. He created a new, temporary ground for the TCM, which immediately caused the CAN Low voltage to drop to a normal 2.8V and cleared the power steering warning. The root cause was a bad ground on the TCM corrupting the entire network's data signals.

OEM Part Supersession History

• 13587704, 13506935, 13506936, 13592137 → 13594764 — Standard part revision and consolidation by the manufacturer.
  Heads up: This Body Control Module is NOT plug-and-play. It must be programmed (cloned) with the original module's data, including the VIN and security information, to function. Swapping a used BCM from another vehicle will cause a no-start condition or other system failures.
• 13518851, 13524378, 13524379, 13524970, 13526301, 13526314, 13532107, 13532121, 13533150 → 13534928 — Standard part revision and consolidation by the manufacturer.
  Heads up: This Serial Data Gateway Module requires programming after installation to ensure it routes network traffic correctly for the specific vehicle's options.