AU
U100004

DTC U100004 indicates the control module detects the CAN bus is in a "Bus Off" state — Qin Plus

Braking System

DTC U100004 indicates the control module detects the CAN bus is in a "Bus Off" state.

In the BYD E5 battery electric vehicle, the ABS system reports this DTC.

It indicates the ABS control unit CAN controller automatically shuts down communication due to an error counter overflow (typically caused by continuous bus errors or interference) to protect the bus from a faulty node.

Consequently, the ABS module cannot exchange data with the vehicle network (including the gateway, VCU, and instrument cluster).

This disables functions such as the anti-lock braking system and electronic stability control (ESC) and illuminates multiple instrument panel warning lamps.

On some other models (such as the S6), U100004 may also indicate a transmission control module (TCU) communication fault, but the core mechanism remains a communication interruption between the control unit and the CAN bus.

4
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Damage or cold solder joints on the internal CAN transceiver chip of the ABS control unit prevent sending or receiving CAN signals.
  • 2Chassis CAN bus wiring (CAN-H/CAN-L) shorted to power, shorted to ground, or shorted together, causing bus blockage.
  • 3Abnormal ABS control unit power supply voltage (battery voltage too high/too low) or poor ground connection, causing abnormal communication module operation.
  • 4Gateway controller fault causing bus impedance mismatch or communication routing error, indirectly triggering ABS node Bus Off.
  • 5CAN bus terminating resistor failure (open circuit or resistance drift), causing signal reflection, communication interference, and error counter accumulation.
What To Do
  • 1
    Use the BYD VDS diagnostic tool to read all fault codes. Confirm whether U100004 is a current or history code, and check for accompanying communication fault codes such as U100308 (EPB CAN communication timeout).
  • 2
    Check the ABS control unit power supply: Measure the constant power (B+) and ignition power (IG) voltages. The voltages must be within 12V ± 0.5V. Ground resistance must be less than 1Ω.
  • 3
    Measure the CAN bus voltage at the OBD port or ABS connector: CAN-H is approximately 2.6-2.7 V, and CAN-L is approximately 2.3-2.4 V. Measure the termination resistance (after disconnecting power): it should be approximately 60 Ω (two 120 Ω resistors in parallel).
  • 4
    Check the ABS control unit 32-pin connector (or corresponding connector) for water ingress, oxidation, or backed-out pins. Clean and apply conductive grease if necessary.
  • 5
    Perform a CAN bus short/open circuit test: measure the resistance and voltage of CAN-H and CAN-L to ground and to power respectively to confirm no short circuits exist.
  • 6
    Perform a power reset: Disconnect the battery negative terminal for at least 5 minutes to clear the ABS control unit CAN controller error counter. Reconnect power and test.
  • 7
    If all above checks are normal but the fault persists, replace the ABS control unit assembly and perform online coding and ESC calibration.
Real-World Cases
BYD DTC AI Analysis

2018 BYD E5 ABS CAN Bus Off Fault

✓
Instrument cluster ABS and ESC warning lights stayed on constantly. VDS retrieved DTC U100004 (CAN bus off). Found pin 15 (CAN-H) at the ABS connector slightly oxidized. Cleaned and reconnected; fault persisted. ABS supply voltage measured normal. Disconnected the battery to reset; fault cleared. Recurred after one week of driving. Replaced the ABS control unit assembly and programmed it; fault completely resolved.
BYD DTC AI Analysis

BYD S6 U100004 Transmission Communication Fault

✓
The dashboard warning light came on. The scan tool read DTC U100004. Per technical documentation, this code relates to the transmission system on this model; the vehicle exhibited harsh shifting. Inspection revealed an internal chip failure in the Transmission Control Module (TCU) interrupting CAN communication. Replaced the TCU; fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Song DM Gateway Communication Fault (Reference Case)

✓
After starting the vehicle, multiple warning lights illuminated simultaneously (engine warning light, ABS light, airbag light, etc.) and some electronic functions failed. The scan tool could not establish communication with multiple control modules. U-category communication DTCs were retrieved. Checked the Gateway module power supply and CAN bus connections and found a loose Gateway connector causing the communication interruption. Reconnected the Gateway module connector, cleaned the terminal oxidation, and resolved the fault.
Original source ↗
BYD DTC AI Analysis

BYD S6 instrument panel communication fault (U100004-type symptoms)

✓
The owner reported inoperative steering wheel buttons, inability to set cruise control, and abnormal instrument cluster displays. Technicians replaced the steering wheel cruise control switch assembly, instrument panel relay assembly, and instrument cluster assembly, but the fault remained. Troubleshooting revealed poor contact in the CAN bus lines between the instrument cluster, BCM, and gateway. Repairing the wiring harness connector resolved the issue. This case demonstrates how CAN bus communication faults can affect multiple modules.
Original source ↗
Other Qin Plus 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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus overview →
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.