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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 8

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.

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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1TCU power supply system fault: Blown TCU power fuse (usually 15A or 20A), open power supply circuit, or poor contact, preventing 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 contact at branch nodes.
  • 3TCU control unit internal fault: damaged internal CAN transceiver, main control chip failure, software crash, or outdated software version causing a communication protocol mismatch.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 issue: TCU or ABS CAN line connector loose, backed-out terminals, water ingress causing oxidation and corrosion (common after driving through water or car washing), or deformed pins causing poor contact.
  • 5Gateway controller fault: Internal vehicle gateway (GWC) fault 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 if U010104 is a current fault. Check for accompanying communication fault codes (such as U0100 or 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 +B) and body ground. Standard value: 10-16V (20-32V for 24V systems). Check the continuity of the TCU ground wiring harness (resistance < 1Ω) and verify the power supply fuse status.
  • 3
    CAN bus physical layer inspection: Measure terminal resistance between diagnostic connector pins 6 (CAN-H) and 14 (CAN-L) (standard 60 ± 5 Ω); measure CAN-H to ground voltage (2.5-3.5 V), CAN-L to ground voltage (1.5-2.5 V), and resistance between CAN-H and CAN-L at the TCU connector; 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
    Circuit continuity and insulation check: Test continuity of the CAN wiring harness from the ABS control unit to the TCU (resistance must be less than 5Ω). Inspect the wiring harness for wear and crushing. Measure the CAN wire insulation resistance to ground and power (must be greater than 10MΩ). Focus on the wiring harness in high-temperature areas of the engine 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 fully seat them (listen for the locking click). Verify the connector sealing rings are intact.
  • 6
    Control unit function test: Attempt a TCU power reset (disconnect the battery negative terminal for 5 minutes); check the TCU software version, and if an update is available, perform an online programming upgrade; use the diagnostic tool to perform a TCU communication test. If the diagnostic tool fails to access the TCU system and the wiring is normal, diagnose a TCU hardware fault.
  • 7
    Component replacement and matching: If the TCU is faulty, replace the TCU assembly. Perform online configuration coding (VIN writing, vehicle model configuration) and the transmission (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

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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

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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

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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

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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 8 Fault Codes
B1108For 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.B1109DTC B1109 indicates an open circuit in the communication line between the air conditioning system PM2.5 air quality sensor (dust concentration sensor) and the air conditioning control unit (AC ECU), or an open circuit within the sensor internal circuitry. Typically located in the air conditioning intake duct, this sensor monitors real-time PM2.5 particle concentration inside and outside the vehicle. It provides data to the automatic air conditioning system for intelligent switching between fresh air and recirculation modes and for controlling the air purification device. During an open circuit fault, the AC ECU cannot receive the air quality signal, triggering the system fail-safe mode. Symptoms typically include failure of the automatic recirculation function, abnormal air purification indicator light operation, or abnormal air quality data displayed on the air conditioning panel. Severe cases may compromise the cabin environment control strategy, but do not directly affect vehicle driving safety.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
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.