U0101 on 2013-2017 Buick Encore: Lost Communication with TCM Causes and Fixes

What's Unique About the 2013-2017 Buick ENCORE

For this generation of Buick Encore and its platform mates (Chevy Trax, Sonic), the U0101 code is very often an electrical connection problem rather than a failed Transmission Control Module. GM has issued multiple Technical Service Bulletins (TSBs), such as #PIP4990C and #PIP4990D, advising technicians to meticulously check for poor terminal pin fit at the transmission connector and the underhood fuse block before replacing any modules. This history suggests that engine vibration and time can lead to micro-disconnects that cause this specific code. The issue is so common that the bulletins explicitly state that the TCM/TEHCM is often replaced unnecessarily.

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 lamp is illuminated
• Vehicle enters 'limp mode,' limiting speed and getting stuck in one gear
• Harsh, erratic, or delayed shifting
• A hard 'clunk' when shifting into Reverse or Drive
• Gear indicator on the dashboard may be blank, show dashes, or be incorrect
• A professional scan tool cannot communicate with the TCM

Most Likely Causes

1. Poor Terminal Fit at Connectors 🔴 High Probability GM TSB #PIP4990D specifically calls out checking terminal pin fit at the main transmission harness connector and the underhood fuse block. These connections can loosen from vibration, causing intermittent communication loss that is hard to trace without performing a 'pin drag' test.
   How to confirm: Visually inspect the pins in the main transmission harness connector and relevant fuse block connections for looseness, corrosion, or damage. A technician will perform a 'pin drag' test using special tools to check the tension of the female terminals. Simply looking at them is often not enough.
   Typical fix: Repairing or replacing the affected connector terminals or the connector pigtail itself. In some cases, applying dielectric grease and re-seating the connector firmly can restore communication. If the fuse block terminals are loose, they may need to be re-pinned or the block replaced.
   Est. part cost: $10-$50
2. Damaged Wiring Harness 🟡 Medium Probability TSB #PIP4990D notes that the wiring harness can rub against sharp edges on the engine or transmission case, leading to chafed or broken wires. This is a common failure point on many modern, compact engine bays.
   How to confirm: Perform a thorough visual inspection of the wiring harness between the ECM, TCM, and fuse block. Check for any signs of rubbing, melting, or physical damage, especially on top of the transmission. Test continuity of the CAN bus wires (typically Tan and Tan/Black) with a multimeter.
   Typical fix: Repairing the damaged section of wire with a solder and heat-shrink, or replacing the entire harness if damage is extensive.
   Est. part cost: $5-$100
3. Poor TCM Ground 🟡 Medium Probability All control modules require a solid ground to function. TSBs point to checking grounds as a key step. These grounds can corrode or loosen over time.
   How to confirm: Locate the primary TCM ground points (often G106 or G107 on GM vehicles) and inspect them for looseness or corrosion. G106 is often located on the frame rail behind the air cleaner assembly. Perform a voltage drop test on the ground circuit to ensure it's providing a solid connection under load.
   Typical fix: Clean the ground point connection down to bare metal, apply a dielectric grease, and securely refasten the ground wire.
   Est. part cost: $0-$5
4. Failed Transmission Control Module (TCM/TEHCM) ⚪ Low Probability
   How to confirm: This should only be considered after all wiring, connector, power, and ground issues have been definitively ruled out by a professional. If a scan tool cannot communicate with the TCM but all its power, ground, and network circuits test good, the module itself is likely faulty.
   Typical fix: Replace the Transmission Control Module (TEHCM), which is located inside the transmission. The new module will require programming to the vehicle's VIN.
   Est. part cost: $350-$800

Rare But Worth Checking

• Low Battery Voltage or Failing Alternator: Control modules are sensitive to voltage. A weak battery or faulty alternator can cause a variety of unpredictable communication codes, including U0101, without there being a fault in the transmission system itself.
• Blown Fuse: A blown fuse supplying power to the TCM will instantly cause a U0101 code. Always check the TCM-related fuses in both the underhood and interior fuse panels before proceeding with more complex diagnostics.
• Internal Fault in Underhood Fuse Block: Beyond loose terminals, the fuse block itself can develop internal cracks or corrosion on its internal bus bars, leading to an intermittent open circuit for the TCM. This is difficult to diagnose but is a known issue on some GM platforms.

Diagnosis Steps

1. Scan for all stored DTCs in all modules. Note any other communication (U-codes) or system codes. A U0101 in multiple modules points towards a wiring break.
2. Check battery voltage and the charging system. Ensure voltage is >12.4V key-on-engine-off and 13.7-14.7V engine running.
3. Inspect all fuses related to the TCM and ECM in the underhood fuse box. Physically remove and check them, and check for tension in the fuse terminals.
4. Perform a thorough visual inspection of the wiring harness running to the transmission. Look for any signs of chafing, melting, or corrosion, especially where the harness may contact the engine block or brackets.
5. Disconnect the main transmission electrical connector (after disconnecting the battery). Look for bent, corroded, or loose pins. Check for any signs of fluid intrusion.
6. Inspect connections at the underhood fuse block, as recommended by TSB #PIP4990D.
7. Locate and inspect the primary TCM ground connections (e.g., G106, G107) for corrosion or looseness. Disassemble, clean, and re-secure them.
8. With a multimeter, check for 12V+ power and good ground (<5 ohms to chassis ground) at the appropriate pins on the TCM connector.
9. Test the resistance of the CAN bus wires. Disconnect the battery. At the OBD-II port, measure resistance between Pin 6 (CAN-H) and Pin 14 (CAN-L). It should be approximately 60 ohms. A reading of 120 ohms indicates a break in the circuit.
🎬 Watch: How to perform a professional communication test on the TCM.
10. If all wiring, connectors, powers, and grounds test good, the final step is to suspect a faulty TCM/TEHCM.

Parts You'll Likely Need

• Transmission Control Module (TCM/TEHCM) (OEM #ACDelco 24265789) — This is the part that needs to be replaced if it has failed internally, but only after all wiring and connection issues have been ruled out. It is located inside the transmission side cover.
  Trusted brands: ACDelco (OEM), Dorman
  OEM price range: $350-$600
  Aftermarket price range: $250-$450
• Wiring Harness Connector Pigtail — If the pins inside the main transmission connector are damaged, corroded, or have lost tension, replacing the connector end (pigtail) is the standard repair.
  Trusted brands: ACDelco, Dorman, Pico
  OEM price range: $40-$80
  Aftermarket price range: $20-$50

Related Codes That Often Appear With This One

• P0700 — P0700 is a generic code set by the ECM to indicate the TCM has stored a fault. It's the ECM's way of turning on the check engine light on behalf of the transmission system. If you see U0101, you will almost always see P0700 as well.

Technical Service Bulletins (TSBs) & Recalls

• PIP4990D: Supersedes previous versions. Advises technicians to check terminal pin fit at the transmission connector and underhood fuse block, inspect for harness chafing, and check TCM grounds (G106, G107) before replacing the TEHCM.
• PIP4990C: An earlier version of the bulletin with the same core advice, pointing to terminal fit and grounds as the likely cause over a failed module.

Platform-Specific Known Issues

• Per TSB #PIP4990D, this vehicle platform is known for poor terminal pin fit at the transmission connector and the underhood fuse block, which can cause an intermittent U0101 code.
• Per TSB #PIP4990D, it is critical to gather all other diagnostic trouble codes from all modules in the vehicle, as the U0101 may be a symptom of a broader network issue.
• Owners have reported that the main harness can rub through on a bracket near the top of the transmission, causing a short in the CAN bus wires. This should be one of the first places to inspect visually.