U0101 on 2015-2020 GMC Yukon: Lost Communication with TCM Causes & Fixes

What's Unique About the 2015-2020 Gmc YUKON

The 2015-2020 GMC Yukon and its GM K2XX truck/SUV siblings have a complex communication network that relies on a Serial Data Gateway Module (SDGM) to manage data between modules. Multiple GM Technical Service Bulletins (TSBs) point to specific, common failures on this platform that trigger U0101. These include a poor ground connection for the Body Control Module (BCM) at a specific location (G218) and logic-lockups or connector failures at the SDGM. These network infrastructure problems are frequently the root cause, making a direct TCM failure less likely than on other vehicles.

Diagnostic Flowchart

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

Symptoms You May Notice

• Check Engine Light is on
• Transmission warning light is on
• Service Stabilitrak message appears
• Vehicle is stuck in one gear (limp mode)
• Harsh or erratic shifting
• PRNDL gear indicator on the dash may be blank or incorrect
• Loss of power steering assist (as it relies on network data)
• Vehicle may not start or may stall
• Instrument panel gauges may fluctuate or go blank intermittently
• Radio and HVAC controls may become inoperative

Most Likely Causes

1. Poor Body Control Module (BCM) Ground at G218 🔴 High Probability This is a well-documented issue cited in GM TSBs #PIT5405B, #PIT5405C and the superseding TSB #18-NA-161. The BCM is a central node in the communication network, and a bad ground can disrupt communication for many modules. The factory design allows sound-deadening insulation to get trapped between the ground eyelet and the body, causing a poor connection.
   How to confirm: Locate the G218 ground, which is a stud on the metal support structure behind the driver's side kick panel, near the speaker. Visually inspect it for looseness or for the black dash insulator mat being pinched under the ground nut. A voltage drop test on the ground circuit can also confirm high resistance.
   Typical fix: Remove the 10mm nut, pull the ground wire eyelet off the stud, and trim away any interfering foam or insulation mat. Clean the terminal, the wire end, and the chassis mounting point to bare metal, then re-secure it tightly.
   Est. part cost: $0-$5
2. Serial Data Gateway Module (SDGM) Logic Lock or Connector Fault 🔴 High Probability GM TSBs #PIT5586G and #PIT5586B specifically mention this module. It can freeze ('logic lock') or have poor terminal connections at its X1 or X2 connector, disrupting all network traffic. The SDGM is located high in the driver's side of the dashboard, often above the BCM.
   How to confirm: A technician would follow the TSB procedure, which may involve a hard reset (disconnecting the battery for 30 minutes) to clear a logic lock. The X1 and X2 connectors at the SDGM must be disconnected and inspected for corrosion, moisture, or backed-out/bent terminals.
   Typical fix: For a logic lock, a battery disconnect may suffice. For connector issues, cleaning or repairing the terminals is required. If the module itself has failed, it must be replaced and programmed.
   Est. part cost: $50-$150
3. Damaged Wiring or Corroded Connectors 🟡 Medium Probability GM TSB #21-NA-149 identifies several specific points where the engine wiring harness can chafe against chassis or engine components. Common chafe points include the ECM/TCM bracket, the driver's side upper control arm, and the shock tower bolt. This can cause shorts in the CAN bus wires.
   How to confirm: Visually inspect the wiring harness in the driver's side wheel well (liner removed) and around the engine, specifically at the points mentioned in TSB #21-NA-149. Check for continuity and resistance on the CAN High and CAN Low wires between the TCM and the diagnostic port. Resistance between the two lines should be approximately 60 ohms (with the battery disconnected).
   Typical fix: Repairing the broken/chafed wire with a solder and heat-shrink, and then protecting the harness with anti-abrasion tape or loom and securing it away from the sharp edge.
   Est. part cost: $5-$50
4. Faulty Transmission Control Module (TCM) ⚪ Low Probability While the TCM (or TEHCM - Transmission Electro-Hydraulic Control Module, as it's integrated with the valve body on 6L80/8L90 transmissions) can fail, it is often misdiagnosed. The network and wiring issues listed above are more common culprits on this platform. A classic sign of internal TEHCM failure is the appearance of multiple solenoid and pressure switch codes at once. 🎬 Watch: How to diagnose and fix lost communication with the TCM.
   How to confirm: This is a process of elimination. If all power, ground, and network wiring to the TCM test good, and it's the only module not communicating, the TCM itself is likely faulty. A professional may bypass the TCM on the CAN bus by jumping the CAN wires at the TCM connector to see if communication with other modules is restored.
   Typical fix: Replace the TEHCM, which is located inside the transmission oil pan. This part requires programming to the vehicle's VIN with a specialized J2534 device.
   Est. part cost: $250-$700
5. Low Battery Voltage or Failing Alternator ⚪ Low Probability Modern vehicles are highly sensitive to voltage. A weak battery or poor charging system can cause random communication codes as modules drop offline. The K2XX platform is known for having electrical issues if battery health is compromised, specifically related to high resistance in the negative battery cable as noted in TSB 18-NA-161.
   How to confirm: Test the battery voltage with the engine off (should be ~12.4-12.6V) and while running (should be ~13.7-14.7V). Perform a loaded voltage drop test on the negative battery cable; if the drop exceeds 200mV while cranking, the cable is faulty and needs replacement.
   Typical fix: Charge or replace the battery, replace the negative battery cable, or replace the alternator if it's not charging correctly.
   Est. part cost: $150-$500

Rare But Worth Checking

• Poor Engine-to-Transmission Ground (G110):

Diagnosis Steps

1. Check and record the battery voltage and perform a load test. Ensure it is above 12.4V and stable.
2. Perform a full vehicle scan to identify all stored trouble codes in all modules. Note if multiple 'U' codes are present, which points to a network-wide issue.
3. Follow TSB #PIT5405C: Locate and inspect the BCM ground G218. It is a stud behind the driver's side kick panel/speaker area. Disassemble, trim away any interfering insulation, clean all contact surfaces to bare metal, and securely re-fasten the 10mm nut.
4. Follow TSB #PIT5586G: Locate the Serial Data Gateway Module (SDGM), typically above the BCM in the driver's side dash. Disconnect the battery for 30 minutes to attempt to clear any 'logic lock'. Inspect the X1 and X2 connectors for any backed-out or corroded terminals.
5. Inspect for wiring harness chafing per TSB #21-NA-149. Remove the driver's side front wheel and wheelhouse liner to get a clear view of the harness routing near the ECM/TCM bracket, upper control arm, and shock tower.
6. Inspect the main wiring harness connectors to the transmission for any signs of corrosion, moisture, or damage.
7. With the battery disconnected, measure the resistance between Pin 6 (CAN High) and Pin 14 (CAN Low) at the vehicle's OBD-II port. A reading of approximately 60 ohms indicates the main bus wiring and terminating resistors are likely intact. A reading of 120 ohms suggests a break in the CAN circuit or a missing terminating resistor.
8. If all wiring, grounds, and the SDGM check out, and U0101 is the only persistent communication code, suspect a faulty TCM/TEHCM.

Parts You'll Likely Need

• Serial Data Gateway Module (OEM #13599318 (supersedes 13509768, 13524297, 13524298, 13599317)) — This module is cited in multiple TSBs for logic lock-ups and connector failures that bring down the communication network.
• Transmission Electro-Hydraulic Control Module (TEHCM) (OEM #Fits 6L80/6L90, multiple PNs exist based on year. e.g., 24275873, 24256939. For 8L90, it is a T87 TCM.) — This is the correct part to replace if the TCM is confirmed to be faulty. It is located inside the transmission pan and requires programming.
• Negative Battery Cable — TSB 18-NA-161 identifies high internal resistance in the negative battery cable as a cause for various electrical issues, including communication DTCs.

Related Codes That Often Appear With This One

• U0100 — Lost Communication with ECM. This often appears with U0101 because if the network is down, multiple modules will lose communication simultaneously.
• U0140 — Lost Communication with Body Control Module. This is a strong indicator that the BCM ground (G218) or the BCM itself is the source of the network failure.
• U0073 — Control Module Communication Bus 'A' Off. This is a general network code indicating the entire high-speed CAN bus is down, reinforcing the likelihood of a systemic issue like a bad ground or gateway module problem.
• U0109 — Lost Communication with Fuel Pump Control Module. This can appear alongside other communication codes when a systemic network issue like a bad ground is present.

Technical Service Bulletins (TSBs) & Recalls

• PIT5405B / PIT5405C: Addresses multiple DTCs including U0101 caused by a poor BCM ground at G218.
• PIT5586B / PIT5586G: Addresses multiple communication DTCs caused by SDGM logic lock or connector terminal issues.
• 21-NA-149: Details procedures for inspecting and repairing engine wiring harness chafing at multiple points on the chassis and engine.

Platform-Specific Known Issues

• TSB #PIT5405C identifies a faulty Body Control Module ground at location G218 as a primary cause for a host of electrical issues, including U0101. The fix involves trimming insulation away from the ground stud.
• TSB #PIT5586G points to the Serial Data Gateway Module (SDGM) as a source of network failure, either from a software 'logic lock' or from poor pin connections at its main connectors.
• TSB #21-NA-149 details common wiring harness chafe points in the driver's side engine bay and wheel well that can lead to short circuits on the CAN bus.

Mechanic-Grade Diagnostic Values

• CAN Bus Network Resistance — expected: ~60 Ohms. Failure: A reading of ~120 Ohms indicates an open in the bus or a missing terminating resistor. A reading near 0 Ohms indicates a short between the CAN High and CAN Low wires. A reading around 45 Ohms could indicate a third resistor on the network or a faulty transceiver.
• CAN Bus Voltage (Key On, Engine Off) — expected: CAN High (Pin 6): 2.5V to 3.5V. CAN Low (Pin 14): 1.5V to 2.5V.. Failure: Voltages outside these ranges, or a CAN High voltage lower than CAN Low, indicate a network fault.
• Negative Battery Cable Voltage Drop — expected: Less than 200 mV (0.2 V). Failure: A voltage drop reading above 200 mV while cranking the engine indicates excessive resistance in the cable, requiring replacement.
• TCM Power Supply Voltage — expected: ~12.0 - 12.6V (Battery Voltage). Failure: Low or no voltage indicates a problem with the power feed wiring or a blown fuse. A voltage drop under load (using a test light) points to high resistance in the circuit.

Scan Tool Commands That Help

• GDS2 (GM Techline Connect): Module Communication Test / Ping Module — Used to actively check if a specific module, like the TCM, is responsive on the network. A 'no response' confirms the communication loss seen by other modules.
• GDS2 (GM Techline Connect): SPS (Service Programming System) — This function is required to program a new TEHCM or SDGM after replacement. The vehicle will not operate correctly until the new module is programmed with the correct VIN and software calibration.

Wiring & Ground Locations

• G218 — Behind the driver's side kick panel, on the metal support structure near the speaker.. This is the primary ground for the Body Control Module (BCM). TSBs #PIT5405C and #18-NA-161 identify it as a common failure point due to trapped insulation, causing widespread network communication faults.
• Serial Data Gateway Module (SDGM) — High in the driver's side dashboard, typically above the BCM and to the left of the steering column.. This module acts as a router for all CAN bus traffic. TSB #PIT5586G points to it for logic-lock and connector issues. For 2017+ models, a bypass harness is available to simplify diagnostics.
• TEHCM Connector — On the Transmission Electro-Hydraulic Control Module (TEHCM), which is located inside the transmission oil pan, mounted to the valve body.. This is the main connection point for all power, ground, and communication lines to the TCM. It must be checked for corrosion or fluid intrusion if the pan is dropped.
• G110 — On the driver's side of the engine block, near the front and behind the power steering pump.. This is a main ground for the ECM/TCM. While less common than G218, a loose or corroded connection here can cause U0101.

Real Owner Repair Stories

• gm-trucks.com forum user (2015 Chevrolet Silverado (K2XX Platform)) — Intermittent no-start, multiple communication codes including U0101, U0100, U0140. Dash would go blank, Stabilitrak warnings.
  ❌ Tried (didn't work) Checked and cleaned ground G218., Replaced battery., Inspected wiring harness for chafing.
  ✅ What actually fixed it The user discovered corrosion inside the underhood fuse block. The main positive cable connection point within the fuse block had developed high resistance, causing voltage drops to multiple systems. Cleaning the corrosion and re-securing the connection resolved all communication issues.

OEM Part Supersession History

• Multiple (e.g., 24256939, 24257213, 24259639) → Multiple (e.g., 24275873, 24276637) — Revisions to address internal component failures and improve reliability of the integrated solenoids and pressure switches.
  Heads up: TEHCMs are specific to year ranges and calibrations (Tag IDs). Installing a TEHCM from a different year group, even if it fits, will cause a no-start, no-shift, or immediate limp mode. The module must be programmed to the vehicle's VIN.
• 13509768, 13524297, 13524298, 13599317 → 13599318 — Internal logic and component updates to prevent freezing ('logic lock') and improve network stability.
  Heads up: The latest part number is generally recommended for replacement to get the most recent hardware/firmware revisions.

Model Year Variations Within This Range

• 2015: Early 2015 models were equipped with the 6-speed (6L80) transmission. Mid-year 2015.5 models introduced the 8-speed (8L90) transmission. The TEHCM part numbers and diagnostic considerations are different between these two transmissions.
• 2017-2020: The Serial Data Gateway Module (SDGM) wiring changed. Diagnosing network issues or installing certain aftermarket devices may require repinning the SDGM connector or using a specific bypass harness (related to IO5/IO6 RPO codes).
• 2018-2020: The 10-speed (10L80) transmission was introduced on some models, which uses a different TCM and has different potential failure points compared to the 6-speed and 8-speed units.