U0101 on 2016-2017 Honda Civic: Lost Communication with TCM Causes & Fixes

What's Unique About the 2016-2017 Honda CIVIC

For the 10th generation Honda Civic (2016-2021), the U0101 code is not just a random electrical fault; it's a well-documented pattern. Honda issued multiple Technical Service Bulletins (TSBs) for the 2016-2017 models specifically pointing to internal failure of the Transmission Control Module (TCM) as the root cause. This makes a faulty TCM a much higher probability on this car compared to the usual suspects like wiring or fuse issues that might cause this code 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

• Vehicle will not crank or start.
• Inability to shift the transmission out of Park.
🎬 Watch: How to manually release your gear shifter if stuck
• Multiple warning lights illuminated on the instrument panel, including the Check Engine Light.
• No gear position indicator (P, R, N, D) displayed on the dash.
• Vehicle may enter 'limp mode', with the transmission stuck in a single gear.
• A hard 'clunk' may be felt when attempting to shift gears.

Most Likely Causes

1. Failed Transmission Control Module (TCM) 🔴 High Probability → Shop Transmission Assembly Honda TSBs A17060C and ATS161101 explicitly state the cause is an 'internal malfunction with the transmission control module (TCM)' for this specific vehicle and year range.
   How to confirm: Use an advanced scan tool to check for communication with the TCM. If the module is unresponsive and power/ground tests are good, the TCM has failed. The presence of code U0038 alongside U0101 is a strong confirmation, as noted in the TSB.
   Typical fix: Replace the Transmission Control Module. For 2016 models, the PCM must also be updated to match the new TCM's software. For 2017 models, only the TCM replacement is required.
   Est. part cost: $300-$600
2. Wiring or Connector Issue ⚪ Low Probability While the TCM is the most likely culprit for this specific vehicle, general CAN bus issues can still occur. Corrosion on connectors or damaged wiring can interrupt communication.
   How to confirm: Visually inspect the wiring harness and connectors going to the TCM for any signs of damage, corrosion, or looseness. Use a multimeter to check for stable power (12.0-12.6V), good ground, and continuity on the CAN bus wires at the TCM connector.
   Typical fix: Repair the damaged section of the wiring harness or clean/replace the faulty connector. Some owners have had success cleaning the TCM connector with contact cleaner.
   Est. part cost: $10-$50
3. Blown Fuse or Power Supply Issue ⚪ Low Probability A weak battery or alternator can cause low voltage conditions that lead to communication codes across many modules, though it's less specific to the U0101 on this Civic.
   How to confirm: Check the vehicle's fuse boxes for any blown fuses related to the TCM or PCM. Test the vehicle's battery and charging system to ensure voltage is stable (above 12.4V with engine off, ~14V with engine on).
   Typical fix: Replace the blown fuse and investigate the cause of the overcurrent. Replace a weak battery or faulty alternator.
   Est. part cost: $1-$200

Diagnosis Steps

1. Connect an OBD-II scanner and check for all stored codes. Confirm the presence of U0101 and look for the companion code U0038.
2. Using an advanced scan tool, attempt to communicate directly with the Transmission Control Module (TCM). If communication fails, this points strongly toward the TCM or its circuits.
3. Check for relevant TSBs (A17060C / 17-012, ATS161101). These confirm a known issue with the TCM for this specific model and year.
4. Inspect the TCM wiring harness and connectors for any visible damage, corrosion, or loose pins. Pay close attention to the main connector on the TCM itself.
5. Using a multimeter and a wiring diagram, verify that the TCM is receiving proper battery voltage (12.0-12.6V with ignition on) and has a solid ground connection at its connector.
6. If power and ground are present but communication is not possible, the TCM is defective, as indicated by the manufacturer TSBs.
7. Replace the TCM. For 2016 models, the PCM software must also be updated using a J2534 device and Honda's i-HDS software.

Parts You'll Likely Need

• Transmission Control Module (TCM) (OEM #28100-5DJ-A06 (2.0L). Supersedes: 28100-5DJ-A01, 28100-5DJ-A02, 28100-5DJ-A03, 28100-5DJ-A04, 28100-5DJ-A05. For 1.5L Turbo models, the part number is 28100-5CG-A07.) — This is the component identified by Honda as having an internal malfunction that causes code U0101 on this specific vehicle.
  Trusted brands: Honda (Genuine OEM)
  OEM price range: $300-$600
  Aftermarket price range: Not Recommended

Related Codes That Often Appear With This One

• U0038 — This code, for 'TM-CAN Malfunction [TCM-PCM]', is specifically cited in Honda TSBs A17060C and ATS161101 as appearing with U0101 when the TCM fails.

Technical Service Bulletins (TSBs) & Recalls

• A17060C (also listed as 17-012): '2016–17 Civic Will Not Come Out of Park or Will Not Start and Sets DTC U0038 and/or U0101'. Confirms internal TCM failure as the cause and specifies different repair procedures for 2016 vs. 2017 models.
• ATS161101: Techline summary article confirming the root cause of no-crank/no-shift with U0101/U0038 is the TCM.

Platform-Specific Known Issues

• Honda TSB #A17060C states that affected vehicles 'will not come out of park, and will not crank and/or start' and that the cause is an 'internal malfunction with the transmission control module (TCM)'.
• Honda TSB #ATS161101 corroborates these symptoms and notes 'THERE’S NO COMMUNICATION WITH THE TRANSMISSION,' concluding 'WE’VE FOUND THE ROOT CAUSE IS THE TCM.'
• Owner Experience: Sudden Failure and Dealer Repair: Multiple owners on forums like civicx.com and Reddit report the sudden onset of this issue. A typical story involves the car working perfectly one moment, then refusing to start after being parked. The dashboard lights up with multiple warnings, the gear selector is locked, and the car is completely immobilized. The resolution is consistently a dealer visit, where the TCM is replaced and programmed, often costing between $800 and $1200.

Mechanic-Grade Diagnostic Values

• CAN Bus Network Resistance — expected: Approximately 60 Ω. Failure: A reading of 120 Ω indicates a missing terminating resistor or a break in one of the CAN lines. A reading significantly lower than 60 Ω (e.g., 40 Ω) suggests an extra terminating resistor or a shorted module.
• CAN Bus Voltage (Key On, Engine Off) — expected: CAN High (to ground): ~2.5V to 3.5V. CAN Low (to ground): ~1.5V to 2.5V.. Failure: Voltages that are stuck high, low, or at battery/ground potential indicate a short in the wiring or a faulty module pulling the bus voltage down.
• TM-CAN Line Continuity — expected: Continuity (less than 1.0 Ω) should exist between the specified pins with the PCM and TCM disconnected.. Failure: No continuity (Open Line/OL) indicates a broken wire in the harness between the PCM and TCM.

Scan Tool Commands That Help

• Honda Diagnostic System (HDS): REPLACE TCM/PCM MENU — This menu is used when physically replacing the Transmission Control Module. It contains functions to save data from the old module and write data (including the VIN) to the new one.
• Honda Diagnostic System (HDS): READ DATA / WRITE DATA — Within the 'REPLACE' menu, 'READ DATA' is used on the old module before removal to save vehicle-specific information. 'WRITE DATA' is used on the new module after installation to transfer this information.
• Honda Diagnostic System (HDS): PCM Idle Learn Procedure — After replacing a major powertrain component like the TCM and updating the PCM (on 2016 models), the idle learn procedure must be performed to allow the engine computer to recalibrate.

Wiring & Ground Locations

• Transmission Control Module (TCM) — Located on top of the transmission assembly, underneath the engine air intake tube and air filter box.. This is the module that has lost communication. Physical access is required to test its connectors for power, ground, and CAN signals, and for replacement.
• Transmission Housing Ground — A primary ground strap connects the negative battery cable directly to a mounting bolt on the transmission case.. This is the main ground connection for the TCM. A loose or corroded ground here can cause a loss of power to the module and trigger communication faults.
• TCM Connector (50-Pin) — The main electrical connector on the TCM itself.. This is where diagnostic tests for CAN signals must be performed. Pin 4 is the TM CAN-H wire, and Pin 12 is the TM CAN-L wire.
• PCM Connector A — The 'A' connector at the Powertrain Control Module (PCM), typically located in the engine bay.. This is the other end of the communication line. Continuity checks are performed between the TCM connector and this one. Pin 21 is TM CAN-H and Pin 20 is TM CAN-L.

OEM Part Supersession History

• 28100-5DJ-A01, A02, A03, A04, A05 → 28100-5DJ-A06 — Part revisions to address the internal malfunction.
  Heads up: All parts in this series are for the 2.0L engine. The part is marked as '(Rewritable)', indicating programming is mandatory.
• 28100-5CG-A01, A02, A03, A04, A05, A06, A07 → 28100-5CG-A08 — Part revisions to address the internal malfunction.
  Heads up: All parts in this series are for the 1.5L Turbo engine. Programming is mandatory upon replacement.

Model Year Variations Within This Range

• 2016 only: When replacing the TCM on a 2016 model, the Powertrain Control Module (PCM) software must also be updated. For 2017 models, only the TCM replacement and programming is required.