U0102 on 2015-2019 Chevrolet Silverado 1500: Causes and Fixes for Lost TCCM Communication

What's Unique About the 2015-2019 Chevrolet SILVERADO 1500

On this generation of Silverado (K2XX), a U0102 code is frequently a symptom of a software glitch or a network wiring fault rather than a failed part. GM has issued multiple Technical Service Bulletins (TSBs) advising that various communication codes can be triggered by software issues in the ECM or a 'logic lock' in the Serial Data Gateway Module (SDGM). TSB PIT5586G specifically points to bent or loose terminals in the SDGM connectors as a cause for a flood of U-codes, including U0102. Furthermore, physical faults like the G218 ground point under the dash and wiring harness chafing are well-documented weak points on this chassis.

Diagnostic Flowchart

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

Generation note: This range covers the end of the third generation (K2XX; 2015-2018 and 2019 'LD' models) and the start of the fourth generation (T1XX; 2019 'New Model'). TSB N192267870 specifically applies to the 2019 T1XX models, where a low battery event can trigger U0102, fixed by an ECM reprogram. TSB PIT5586G, regarding the SDGM, is highly relevant to the K2XX platform vehicles.

Symptoms You May Notice

• "Service 4 Wheel Drive" or "Service Transfer Case" message on the instrument cluster.
• Check Engine Light is on.
• 4WD selector switch lights are inoperative or do not change.
• Inability to shift into or out of 4WD.
• Other warning lights, like ABS or StabiliTrak, may be illuminated.
• Gauges on the instrument panel may fluctuate (if the root cause is a broader network issue).
• Radio may not shut off when door is opened or display may be blank.

Most Likely Causes

1. ECM or SDGM Software/Logic Issue 🔴 High Probability GM has issued specific TSBs for this platform. TSB #N192267870 notes that a low battery event on 2019 models can cause a host of U-codes (U0101, U0102, U0129, U0140, U18A2) resolved by reprogramming the ECM. TSB #PIT5586G points to a 'logic lock' state or poor connector terminals at the Serial Data Gateway Module (SDGM) causing similar issues across many modules.
   How to confirm: Check the vehicle's VIN against known TSBs. A dealership or a shop with advanced scan tools can check the current software calibration level and check for communication with all modules. A 'hard reset' by disconnecting the battery for 30 minutes may temporarily restore communication if it's a logic lock.
   Typical fix: Reprogram the affected module (ECM or SDGM) with the latest software. This must be done by a dealership or a qualified repair shop. In the case of PIT5586G, the fix may be repairing bent or loose terminals at the SDGM X1 or X2 connectors.
   Est. part cost: $0-$50
2. Wiring or Connector Issue 🔴 High Probability The TCCM and its wiring harness are located under the truck, exposed to the elements. The harness is known to chafe against the front driveshaft or the transmission housing. The TCCM connector itself (X213) is also prone to moisture intrusion and corrosion.
   How to confirm: Visually inspect the wiring harness running to the TCCM for chafing, especially where it passes near the front driveshaft and over the transmission. Disconnect and inspect the TCCM connector for green/white corrosion or backed-out pins.
   Typical fix: Clean corroded connectors with electrical contact cleaner and apply dielectric grease. Repair damaged wires using solder and heat shrink. Secure the harness away from any moving parts with zip ties to prevent future damage.
   Est. part cost: $5-$50
3. Poor Ground Connection 🔴 High Probability Corrosion or loose bolts at major chassis grounds are a known issue. TSB #PIT5405C specifically addresses ground G218 in the driver's footwell, where the dash insulator mat can get trapped under the ground nut, causing a poor connection and widespread communication DTCs. Broken wires at the main engine block ground are also reported.
   How to confirm: Locate ground G218 under the driver's side dash, near the A-pillar speaker. Remove the nut and check if the foam insulation is interfering with the connection. Perform a voltage drop test on the ground circuit to confirm its integrity.
   Typical fix: Disassemble, clean, and securely re-tighten the ground connection. For G218, permanently trim away the section of the insulator mat that is causing interference before retightening the nut.
   Est. part cost: $0-$5
4. Failed Transfer Case Control Module (TCCM) ⚪ Low Probability While possible, outright failure of the TCCM is less common than software, wiring, or ground issues on this platform. It should only be suspected after all other causes are ruled out.
   How to confirm: After verifying good power, ground, and CAN bus wiring to the module, a professional scan tool that cannot communicate with the TCCM points to an internal module failure.
   Typical fix: Replace the Transfer Case Control Module. The new module must be programmed to the vehicle's VIN using GM's Service Programming System (SPS). Some vendors sell pre-programmed modules.
   Est. part cost: $150-$400

Rare But Worth Checking

• Loose Pin in CAN Bus Junction Connector:

Diagnosis Steps

1. Perform a full vehicle DTC scan to see which other modules are reporting communication loss. Multiple 'U' codes point towards a network-wide issue, likely related to the SDGM or a primary ground.
2. Check for applicable Technical Service Bulletins (TSBs) like N192267870 and PIT5586G. If a TSB matches, follow its procedure first.
3. Perform a 'hard reset' by disconnecting the negative battery terminal for at least 30 minutes. This can sometimes clear a 'logic lock' state in the SDGM.
4. Check the fuses related to the 4WD system (often labeled TREC or 4WD) in the under-hood fuse block.
5. Inspect the battery terminals for looseness and corrosion and ensure the battery has a full charge (at least 12.6 volts). A low voltage event is a known cause for these codes.
6. Visually inspect the wiring harness and electrical connector at the TCCM, located on the driver's side frame rail. Look for chafing (especially near the driveshaft), corrosion, or loose pins.
7. Inspect ground G218. Remove the driver's side sill plate and pull back the carpet/insulation by the A-pillar. Check if the foam insulation is trapped under the ground nut. If so, trim the foam, clean the contact surfaces, and retighten the nut.
8. Inspect the connectors at the Serial Data Gateway Module (SDGM), located behind the dash to the left of the steering column, for poor terminal contact or bent pins, as per TSB PIT5586G.
9. If wiring appears intact, use a multimeter to verify battery voltage and a good ground at the TCCM connector.
10. If power and ground are good, test the CAN bus resistance by measuring between pins 6 and 14 at the OBD-II port 🎬 Watch: Professional diagnostic walkthrough for the U0102 communication code. (key off). The reading should be approximately 60 ohms. A reading of 120 ohms indicates an open circuit.
11. If all wiring, power, and grounds test good, the final step is to suspect a faulty TCCM or a required software update.

Parts You'll Likely Need

• Transfer Case Control Module (TCCM)

Related Codes That Often Appear With This One

• U0101 — Lost Communication with TCM. Both codes often appear together when there is a broader network issue, like a software glitch or a problem with the Serial Data Gateway Module (SDGM), as noted in TSB #N192267870.
• U0140 — Lost Communication with BCM. This code appearing with U0102 strongly suggests a network-wide problem, such as a faulty SDGM, a bad ground (like G218), or a wiring issue at a central connector, rather than an isolated TCCM fault.
• U0073 — Control Module Communication Bus 'A' Off. This is a general network code indicating the entire high-speed CAN bus is down, often caused by a wiring short, a bad ground, or a fault in a terminating resistor.

Technical Service Bulletins (TSBs) & Recalls

• N192267870
• PIT5586G
• PIT5405C

Platform-Specific Known Issues

• TSB #N192267870: On 2019 'New Model' (T1XX) trucks, a low battery voltage event can cause multiple communication codes (U0101, U0102, U0129, U0140, U18A2). The official fix is to reprogram the Engine Control Module (ECM).
• TSB #PIT5586G: A 'logic lock' state in the Serial Data Gateway Module (SDGM) or bent/backed-out terminals in its X1/X2 connectors can cause a loss of communication with numerous modules, setting a wide range of U-codes including U0102.
• TSB #PIT5405C: Specifically identifies an issue where the front dash insulator mat can get trapped under ground G218 (driver's footwell), causing a poor connection and leading to various communication DTCs.

Mechanic-Grade Diagnostic Values

• High-Speed GMLAN Bus Resistance — expected: 60 Ω (± 5 Ω). Failure: A reading of ~120 Ω indicates an open in the bus or a missing terminating resistor. A reading significantly less than 60 Ω suggests a short between the CAN high and low wires.
• TCCM Ground Circuit Voltage Drop — expected: < 100-200 mV. Failure: A reading higher than 200 mV indicates excessive resistance in the ground circuit, which can cause communication faults.
• CAN Bus Voltage (Key On, Engine Off) — expected: CAN High (Pin 6): ~2.7V, CAN Low (Pin 14): ~2.3V. Both should total ~5V.. Failure: A line stuck near 0V or 5V, or voltages that do not add up to approximately 5V, indicates a hard fault (short or open) on the bus.
• TCCM Power Supply Pin — expected: 12V (± 0.5V). Failure: Low or no voltage points to a blown fuse (e.g., F31DL), a bad relay, or an open in the power supply wire.

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Module Diagnostics > Transfer Case Control Module > Data Display — To see if the scan tool can establish communication with the TCCM at all. If data is displayed, it suggests the module is online and the issue may be intermittent or related to another module. If it shows 'No Communication', it confirms the TCCM is offline.
• GDS2 (GM Global Diagnostic System 2): Module Diagnostics > Transfer Case Control Module > Configuration/Reset Functions > Range Actuator Position Learn — After replacing the TCCM or the transfer case actuator. This procedure is required to teach the new module the physical positions of the actuator, and failure to perform it can result in a C038D code alongside the U0102.
• GDS2 (GM Global Diagnostic System 2): Vehicle DTC Information — As the very first step. This function queries all modules on the network and displays which ones have set DTCs. Seeing multiple modules with 'U' codes is a strong indicator of a network-wide problem (like the SDGM or a ground) rather than an isolated TCCM failure.

Wiring & Ground Locations

• G218 — Under the driver's side dash, behind the kick panel near the A-pillar speaker. It is a stud with a nut securing one or more ground eyelets.. This is a major body ground. TSB #PIT5405C identifies that the dash insulator mat can get trapped under the ground nut, causing a poor connection and widespread communication DTCs, including U0102.
• Serial Data Gateway Module (SDGM) — Behind the dashboard, to the left of the steering column, often near the Body Control Module (BCM). It has two main connectors, typically black (X1) and gray (X2).. This module acts as a traffic cop for all network communication. TSB #PIT5586G notes that a 'logic lock' or poor terminal contact in its connectors can cause a flood of U-codes, making it a primary suspect when U0102 appears with other communication codes.
• Transfer Case Control Module (TCCM) — For the K2XX platform (2015-2019 LD), the TCCM is typically mounted on the driver's side frame rail, near the transmission crossmember, under the truck.. This is the module that has lost communication. Its location makes its wiring harness and connector (X213) highly susceptible to road debris, moisture, and chafing against the frame or front driveshaft.
• G102 Engine Ground — On the rear of the left (driver's side) engine block or cylinder head.. A critical engine ground. A broken wire at this ground's ring terminal is a known failure that can cause intermittent stalling and widespread communication codes as the engine torques, disrupting the ground reference for multiple modules.

Real Owner Repair Stories

• YouTube channel 'WillPowered Garage' (similar GM truck platform) (2007-2014 GM Truck/SUV (Tahoe shown)) — Engine would stall when shifting into reverse, oil pressure would drop, and eventually set U0100, U0101, and U0102.
  ❌ Tried (didn't work) Suspected oil pressure issue, dropped oil pan, checked pickup tube and screen.
  ✅ What actually fixed it The root cause was a broken ground wire for the G102 ground on the driver's side engine block. One of the smaller wires in the bundle had broken all its strands inside the insulation right at the ring terminal. The connection was intermittent, failing only when the engine torqued in reverse. The fix was to cut off the old ring terminal and splice in a new one.
• Forum user on silveradosierra.com (2015 Sierra) — Service 4WD light, U0102 code.
  ❌ Tried (didn't work) Replacing the TCCM, Checking fuses
  ✅ What actually fixed it The wiring harness running over the transmission had chafed through, causing a short. Repairing the damaged wires and securing the harness away from the sharp edge resolved the code.

Model Year Variations Within This Range

• 2019+ (T1XX Platform): On 2019+ models, the DLC (OBD-II port) may not be directly tied into the main high-speed CAN bus for resistance testing. Measuring between pins 6 and 14 might only show the 120 Ω resistance of the Serial Data Gateway Module, not the full 60 Ω of a properly terminated network. This is a significant change from the K2XX platform where 60 Ω is the expected reading at the DLC.