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U010004

U010004 is an ISO 14229 CAN bus communication fault code — Qin Plus

Braking System

U010004 is an ISO 14229 CAN bus communication fault code.

It indicates the ESP (Electronic Stability Program) module detects a data validation error (CRC error), sequence error, or abnormal Data Length Code (DLC) when receiving a CAN data frame from the ECM (Engine Control Module, or the Vehicle Control Unit [VCU] / Motor Control Unit [MCU] in New Energy Vehicles).

This compromises data integrity.

Unlike U0100 (communication timeout), this fault indicates a physical connection exists but the data content is corrupted.

On BYD hybrid and battery electric platforms, this prevents the ESP from obtaining accurate motor torque, speed, or engine operating condition information.

This condition can trigger brake system downgrade mode (limiting ABS/ESP functions), disrupt energy recovery and brake coordination control, and in severe cases, cause power interruption or limp mode.

The U010004 fault code on the Qin Plus indicates a medium-severity CAN bus data communication problem between the ESP and ECM/VCU/MCU. The connection may still exist, but the data is corrupted, which can affect ABS/ESP, brake energy recovery, or cause limp mode. Common causes include damaged CAN-H/CAN-L wiring or a faulty CAN transceiver inside the control module. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1CAN bus physical layer fault: CAN-H and CAN-L lines open, shorted together, or shorted to power or ground, compromising signal integrity.
  • 2ECM/EMS module internal CAN transceiver damaged: Internal communication chip fault causes transmission of error frames or corrupted data packets.
  • 3ESP module CAN receive circuit fault: ESP-side CAN controller or transceiver is faulty, incorrectly identifying normal data as erroneous data.
  • 4Poor wiring harness connector contact: Oxidation, backed-out pins, or loose connections at the ECM or ESP module harness connectors cause bit errors during signal transmission.
  • 5Electromagnetic interference (EMI): EMI from operating high-voltage systems (such as the motor, DC-DC converter, or air conditioning compressor) couples into the CAN bus and corrupts data frames.
What To Do
  • 1
    Read complete fault codes using the diagnostic tool: confirm if U010004 is a current or historical code, check the ECM/VCU and other modules (TCU, BMS) for stored related communication fault codes, and analyze the freeze frame data recorded at the time of the fault.
  • 2
    Measure CAN bus physical layer parameters: Use a multimeter to measure CAN-H (approx. 2.6–2.8 V) and CAN-L (approx. 2.2–2.4 V) voltage to ground. Measure terminal resistance (measure across the lines after power-off; standard value is approx. 60 Ω, single module is 120 Ω). Use an oscilloscope to check the waveform for distortion, spikes, or abnormal bit width.
  • 3
    Check the wiring harness and connectors: Focus on the ECM and ESP hydraulic unit connectors in the engine compartment, and inspect the pins for oxidation, backing out, or looseness; inspect the wiring harness for signs of abrasion, crushing, or water ingress; measure the continuity and insulation of the CAN lines between the ECM and ESP.
  • 4
    Perform a network isolation test: Disconnect other modules on the CAN network one by one (such as the BMS, TCU, and A/C controller). Observe whether U010004 disappears to rule out other modules interfering with communication by sending error frames.
  • 5
    Module replacement verification: If wiring measurements are normal, test with a known good ECM (or VCU) or ESP module to confirm if the fault transfers with the module. For hybrid models, also check the high-voltage system shield ground connection.
  • 6
    Software and calibration check: Check ECM and ESP module software versions; upgrade or reflash if necessary. Write CAN network configuration (Coding) and perform the ESP calibration procedure.
Real-World Cases
BYD DTC AI Analysis

BYD G6 ESP System Warning with Communication Fault

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Symptoms: Dashboard suddenly displayed 'Check ESP System' while driving. Warning returned after a few kilometres once codes were cleared. Diagnosis: ESP module stored historic DTC U010004 (EMS timeout). CAN bus voltage measured low 2.3V/high 2.7V and termination resistance 60Ω, both normal. Found slight oxidation on the ABS pump harness connector. Fix: Cleaning and tightening the ABS pump harness connector made no difference. Fault traced to internal communication failure in the engine control module. Replacing the engine ECU completely resolved the issue.
Original source ↗
BYD DTC AI Analysis

BYD S7 intermittent ESP warning light and multi-system communication fault

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Symptoms: ESP warning light illuminates intermittently with no discernible pattern. Diagnosis: ESP module logged DTC U010004 (EMS timeout, historical) and U012604 (SAS CAN communication timeout). TCU logged U1701 (communication failure with ECM). Engine system showed no DTCs. Root cause is intermittent interruption in CAN communication between ECM, ESP module, and TCU. Resolution: Inspection found loose CAN communication wiring harness connector between EMS and ESP module with pins slightly backed out. Repaired poor connection; fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Song petrol variant won't start with history DTCs

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Symptoms: 2016 BYD Song petrol manual fails to start, presenting as fuel starvation with stored U010004 fault in engine system. Diagnosis: Engine fires when spraying cleaner at throttle body, ruling out pure communication issue; live data shows abnormal fuel pressure, while U010004 indicates previous ECM communication fault. Solution: Low-pressure fuel pump malfunctioning, causing insufficient fuel supply; replaced low-pressure fuel pump to restore starting; checked ECM communication wiring to prevent U010004 from recurring.
Original source ↗
BYD DTC AI Analysis

BYD Song DM: Multiple system warnings and power interruption while driving

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Symptoms: Transmission fault, flashing P indicator, HDC warning and electronic park brake warning appeared suddenly while driving. Vehicle would not move. Diagnosis: No communication with VBU (Vehicle Control Unit). Front motor controller logged U014100 (lost communication with VBU). TCU and other modules reported communication faults with ECM (related U010004 faults). Diagnosed as CAN network failure causing ECM/VBU to lose communication with multiple systems. Resolution: Found poor contact in the CAN backbone wiring harness connector for the vehicle control unit. Reseated and secured the connector. All system communications returned to normal.
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.