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U010004

U010004 is an ISO 14229 CAN bus communication fault code — Atto 3

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.

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Cases Logged
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.
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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.
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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 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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.