AU
U010104

U010104 is a powertrain CAN bus communication fault code indicating the ABS (Anti-lock Braking System) control unit cannot establish normal communication with the TCU (Transmission Control Unit / Motor Control Unit) via the CAN bus — Atto 3

Braking System

U010104 is a powertrain CAN bus communication fault code indicating the ABS (Anti-lock Braking System) control unit cannot establish normal communication with the TCU (Transmission Control Unit / Motor Control Unit) via the CAN bus.

Although the BYD E5 pure electric model uses a fixed-ratio reducer instead of a conventional transmission, the TCU designation typically refers to the drive motor control unit (MCU) or the reducer control module.

This fault prevents the ABS system from obtaining real-time powertrain data, such as motor speed, torque output, and gear position status.

This data loss restricts regenerative braking and disrupts ESC (Electronic Stability Control) coordination.

Severe cases may trigger limp mode or cut power output.

Information exchange between the ABS and TCU is critical to vehicle dynamic control; repair this fault immediately.

4
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1TCU power supply system fault: Blown TCU power fuse (usually 15A or 20A), open circuit, or poor contact in the power supply circuit prevents normal TCU operation.
  • 2CAN bus physical layer fault: Powertrain CAN-H or CAN-L line shorted to ground or power, wiring harness open circuit, abnormal terminating resistance (standard value 60Ω), or poor branch node contact.
  • 3TCU control unit internal fault: Damaged internal CAN transceiver, main control chip failure, software crash, or outdated software version causing a communication protocol mismatch.
  • 4Wiring harness connector issues: Loose TCU or ABS CAN line plug, backed-out terminals, water ingress causing oxidation and corrosion (common after wading or car washing), or deformed pins causing poor contact.
  • 5Gateway controller fault: An internal fault in the vehicle gateway (GWC) interrupts data routing between the powertrain network (PT-CAN) and the chassis network (Ch-CAN).
What To Do
  • 1
    Fault Confirmation and Freeze Frame Reading: Use a VDS2000 or Launch X431 diagnostic tool to read all fault codes and freeze frame data. Confirm whether U010104 is a current fault. Check for accompanying communication fault codes (e.g., U0100, U0121). Record parameters such as vehicle speed and voltage at the time of the fault.
  • 2
    TCU power supply and ground check: Disconnect the TCU connector and measure the voltage between the TCU power supply pin (constant power +B) and body ground. The standard value is 10-16V (20-32V for 24V systems). Check the continuity of the TCU ground wiring harness (resistance must be less than 1Ω) and verify the power supply fuse condition.
  • 3
    CAN bus physical layer inspection: Measure the terminating resistance between pin 6 (CAN-H) and pin 14 (CAN-L) of the diagnostic connector (standard: 60 ± 5 Ω). At the TCU connector, measure the CAN-H voltage to ground (2.5–3.5 V), CAN-L voltage to ground (1.5–2.5 V), and the resistance between CAN-H and CAN-L. Use an oscilloscope to verify the CAN waveform is normal (dominant level: CAN-H 3.5 V / CAN-L 1.5 V, recessive level: 2.5 V).
  • 4
    Harness continuity and insulation check: Test continuity of the CAN harness from the ABS control unit to the TCU (resistance must be less than 5 Ω). Inspect the harness for wear and crushing. Measure the insulation resistance of the CAN lines to ground and to the power supply (must be greater than 10 MΩ). Focus on the harness in high-temperature areas of the motor compartment and body pass-through holes.
  • 5
    TCU and ABS connector inspection: Inspect the TCU and ABS control unit connectors for signs of water ingress (green oxidation) and backed-out or deformed pins; clean the connectors with electrical contact cleaner, apply conductive grease, and seat them fully (listen for the locking click); verify the connector sealing rings are intact.
  • 6
    Control unit function test: Perform a TCU power reset (disconnect the negative battery terminal for 5 minutes). Check the TCU software version. If an update is available, perform an online programming upgrade. Use the diagnostic tool to perform a TCU communication test. If the tool cannot access the TCU system and the wiring is normal, the TCU hardware is faulty.
  • 7
    Component Replacement and Matching: If the TCU is faulty, replace the TCU assembly. Perform online configuration coding (write VIN, configure vehicle model) and the gearbox (reducer) self-learning procedure. Clear all fault codes. Perform a road test to verify normal ABS and ESC operation and confirm the fault does not recur.
Real-World Cases
BYD DTC AI Analysis

BYD Song DM: Blown TCU fuse caused communication interruption

✓
Symptoms: Vehicle powered on. Dashboard displayed 'Powertrain System Fault' and the vehicle could not drive. Scan tool read DTC U010104 (Lost Communication with TCU). Diagnosis: Checked TCU power supply circuit and found the 15A TCU fuse blown. Replaced fuse but fault persisted. Further inspection revealed water ingress and corrosion in the TCU connector, causing an internal short that blew the fuse. Repair: Replaced TCU fuse, cleaned corroded terminals in the TCU connector and sprayed electronic cleaner, then sealed the connector to prevent water ingress. Fault completely resolved.
BYD DTC AI Analysis

BYD Qin Pro: Loose TCU connector causes intermittent communication failure

✓
Symptoms: Vehicle intermittently failed to start. Instrument cluster displayed "Check Power System". Scan tool could not read TCU data. Diagnosis: Performed DTC U010104 diagnostic procedure per workshop manual. TCU power and ground checked normal. TCU CAN line resistance measured 60Ω (normal). Found TCU connector not fully seated—locking tab was damaged, causing communication dropout when the vehicle hit bumps. Repair: Reseated TCU connector, replaced locking tab, and secured wiring harness with cable ties to prevent loosening. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Tang DM powertrain CAN wiring harness chafed and shorted

✓
Symptoms: Sudden loss of power while driving, multiple warning lights illuminated on the instrument cluster, DTC U010104 (lost communication with TCU) stored. Diagnosis: Powertrain CAN bus voltage measured abnormal (CAN-H at 0V, CAN-L at 5V). Sectional inspection of the CAN bus revealed damaged insulation on the CAN-H line at the TCU, causing a short to chassis ground and complete powertrain CAN network failure. Resolution: Repaired the damaged CAN-H wiring, re-wrapped the harness and rerouted it to avoid contact with sharp chassis edges. Fault resolved.
BYD DTC AI Analysis

BYD e5 pure electric: TCU internal failure causing complete loss of communication

✓
Symptoms: Vehicle powered on but OK light did not illuminate. Unable to shift into gear or drive. Scanner read DTC U010104 (Lost Communication with TCU). Diagnosis: Checked TCU power supply and ground – normal. Measured CAN bus resistance and voltage – both normal. Oscilloscope showed no CAN waveform output from TCU. TCU software version outdated; upgrade attempt interrupted. Confirmed TCU internal CAN transceiver failed. Resolution: Replaced transmission control unit (TCU) assembly. Performed online programming and configuration. Completed transmission self-learn procedure. Fault resolved.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For the BYD Song MAX (2017–2019), DTC B1108 indicates a short circuit in the PM2.5 air quality detection module (dust sensor) or its wiring harness. The sensor uses laser scattering to detect in-cabin and outside PM2.5 concentrations and transmits data to the HVAC ECU via the LIN bus or an analog signal. Short circuit conditions include: 1) Sensor power supply wire (+5V/+12V) shorted to ground 2) Signal wire shorted to power or ground 3) Short circuit in the sensor's internal photoelectric detection circuit This fault prevents the automatic climate control from switching between fresh air and recirculation based on air quality. The system enters fail-safe mode (typically forced recirculation). Severe short-circuit current can destroy the HVAC ECU sampling circuit. The system classifies this as a Level 3 severe fault and restricts vehicle operation to prevent electrical fires or controller damage. For other BYD models (such as the Qin EV, E5, and Song DM), B1108 indicates a driver-side sunload sensor fault, reflecting differences in DTC definitions across models.B110811This DTC indicates a short circuit in the air conditioning system PM2.5 air quality sensor (rapid detector). Specifically, abnormal continuity exists between the sensor power supply circuit or signal output circuit and body ground or battery positive. This causes the control module (ACU/air conditioning controller) to detect abnormal current or a voltage signal outside the valid range (typically 0V or supply voltage). The PM2.5 sensor monitors internal and external particulate concentrations, providing the data the automatic air conditioning system uses to switch between fresh air and recirculation modes. A short circuit disables the air quality monitoring function. This fault may force the air conditioning system into recirculation protection mode and trigger related thermal management system faults, as the air conditioning system acts as a key actuator in vehicle thermal management. In severe cases, the short circuit current can damage the internal sampling circuit of the air conditioning controller or overheat the wiring harness.
Data confidence: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.