AU
U010108

U010108 is a BYD-specific extended fault code and a subclass of the U0101 communication fault series — Seal U

Braking System

U010108 is a BYD-specific extended fault code and a subclass of the U0101 communication fault series.

It indicates the ABS (Anti-lock Braking System) control unit detects a data integrity check failure when receiving CAN messages from the TCU (Transmission/Drive Control Unit; in E5 battery electric vehicles, this typically refers to the motor controller MCU or transmission management unit).

Although the ABS module receives the CAN signal from the TCU, the message contains a CRC checksum error, a non-continuous Live Counter, a byte length violating protocol specifications, or out-of-range key signal values (such as motor speed, output torque, or gear status).

This prevents the ABS from accurately obtaining real-time powertrain parameters, affecting regenerative braking and ESC (Electronic Stability Control) coordination.

In severe cases, the system triggers Limp Home mode and limits motor power to ensure safety.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1TCU/MCU internal software defect or hardware clock drift causing abnormal timing or checksum values in transmitted CAN messages.
  • 2CAN bus physical layer interference (wiring harness wear causing a short circuit, electromagnetic interference, or abnormal terminating resistance) causes bit errors or lost data frames during transmission.
  • 3TCU supply voltage fluctuation (low auxiliary battery charge, unstable DC-DC output) or excessive ground circuit resistance causes CAN signal level offset and sampling errors at the receiving end.
  • 4Loose connection, backed-out terminal, or water ingress and oxidation at the front compartment wiring harness connector (especially the TCU wiring harness plug near the front compartment power distribution box on E5 models) causing poor signal contact.
  • 5Mismatched ABS control unit or TCU software versions cause differences in the communication matrix definition, resulting in data parsing errors.
What To Do
  • 1
    Use the VDS1000 diagnostic tool to perform a full vehicle scan and confirm if U010108 is a current active fault. Check for accompanying U0101 (Lost Communication With TCU) or U0073 (CAN Bus Off) codes, and record the freeze frame data.
  • 2
    Check the power supply voltage (+B, IG1) and ground wires of the TCU (located in the front compartment) and the ABS control unit (located near the engine compartment firewall). The standard voltage is 12V ± 0.5V, and the ground resistance must be less than 1Ω. On E5 models, check the mating connector between the front compartment wiring harness and the body wiring harness for oxidation.
  • 3
    Measure the resistance between pin 6 (CAN-H) and pin 14 (CAN-L) of the OBD diagnostic port. The standard value is approximately 60 Ω (two 120 Ω terminating resistors in parallel). Check for a short to ground, a short to power, or an open circuit. On E5 models, the ABS and BMS (or VCU) usually contain the terminating resistors.
  • 4
    Disconnect the TCU and ABS wiring harness connectors. Check for backed-out pins, corrosion, or signs of water ingress. Measure CAN line continuity between the TCU and ABS (resistance should be less than 5 Ω). If necessary, use an oscilloscope to monitor the CAN waveform for abnormal interference or signal reflection.
  • 5
    Check the TCU software version, compare it against the latest BYD technical bulletin (e.g., TSB), and update the TCU or ABS control unit software. If the fault persists, replace the TCU assembly and recalibrate the powertrain network.
Real-World Cases
BYD DTC AI Analysis

BYD Song — Multi-System Fault Warning

✓
While driving, the dashboard suddenly displayed multiple warnings: "Check Engine System", "ABS System", "Network", and "Braking System". VDS1000 scan showed U0101 series communication faults in the ECM. CAN network voltage check revealed an intermittent open circuit in the PT-CAN data bus. The front compartment wiring harness had poor contact under engine vibration. Replaced the engine wiring harness and front compartment wiring harness, secured the harness routing to prevent rubbing. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Qin 80 – Intermittent failure to enter Ready mode

✓
While driving, the P gear light flashed intermittently, the SOC did not display, and the instrument panel showed multiple system faults; the vehicle failed to enter OK mode. VDS diagnosis found communication timeouts in multiple modules, including abnormal ECM and VCU communication. CAN-H and CAN-L circuit resistance measured greater than 60Ω, indicating abnormal termination resistance. The Gateway (GW) module power supply showed intermittent IG1 power loss. Replaced the instrument panel power distribution box, repaired the Gateway module power supply circuit, and recalibrated the VCU.
Original source ↗
BYD DTC AI Analysis

BYD Tang DM - Erratic dashboard, no EV mode

✓
While driving in EV mode, the engine suddenly started and the instrument cluster showed erratic fault messages. Powered down and restarted; system returned to normal. VDS scan showed communication errors with ECM, TCU, instrument cluster, drive controller, BUS, EPS, and ESP modules. Measured CAN voltages at the diagnostic port: CAN-H 2.6V, CAN-L 2.4V — essentially normal. Disconnected modules one by one to isolate the fault; traced CAN signal interference to the battery management system (BMS). Checked the high-voltage interlock loop and found poor contact at the service switch socket causing the interference. Replaced the service switch socket, cleaned the BMS connector, and retightened the high-voltage interlock wiring.
Original source ↗
BYD DTC AI Analysis

BYD Song Pro - Instrument cluster shows 'Key not detected', won't start

✓
The rotating PAD screen remained lit. The vehicle failed to restart, with the instrument cluster displaying "Key not detected". A VDS scan revealed multiple communication timeout faults from the gateway module, including communication failure with the ECM. Inspection found the right domain controller (with integrated gateway function) had outdated software. Testing identified signal reflection on the CAN bus under specific operating conditions. Upgraded the right domain controller software to the latest version and replaced the gateway module with an improved unit.
Original source ↗
BYD DTC AI Analysis

BYD Qin Plus EV - Air Conditioning Not Cooling With Communication Fault

✓
AC not cooling. VDS scan of right domain controller showed U0101 communication faults. AC controller (integrated in right domain) inoperative. No AC system fault codes, but right domain reported abnormal ECM communication. Measured right domain supply voltage: excessive voltage drop on constant power (exceeding 0.5V). Found oxidation at battery negative ground point causing insufficient module power. Cleaned and tightened battery negative ground point, checked all module supply circuits. Fault resolved.
Original source ↗
Other Seal U 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.