AU
U043204

DTC U043204 indicates a communication timeout between the IPB (Intelligent Integrated Braking System) control unit and the MMx_TX module (Multi-axis Acceleration Sensor) — Atto 3

Braking System

DTC U043204 indicates a communication timeout between the IPB (Intelligent Integrated Braking System) control unit and the MMx_TX module (Multi-axis Acceleration Sensor).

The MMx module monitors the vehicle’s lateral and longitudinal acceleration, providing critical dynamic data for ESP, Automatic Emergency Braking (AEB), Electronic Brakeforce Distribution (EBD), and the brake energy recovery system.

The IPB main control unit triggers this fault if it fails to receive valid acceleration data within the specified communication cycle (usually 200 ms), or if the received data frame contains a checksum error or abnormal length.

The system enters a safety fallback mode, limiting or disabling advanced functions such as ESP and AEB.

The vehicle usually retains basic hydraulic braking, allowing cautious driving to a repair facility.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Multi-axis acceleration sensor (MMx) power supply circuit fault (5V reference voltage abnormal or missing) or poor ground connection, preventing normal sensor initialization or continuous operation.
  • 2Physical damage, open circuit, or short circuit in the CAN bus communication lines, or backed-out pins, oxidation, or corrosion from water ingress in key intermediate connectors (such as KJG05, BJA01) resulting in excessive contact resistance.
  • 3Multi-axis acceleration sensor damaged (internal MEMS chip fault, cold solder joint, moisture ingress due to seal failure, or performance degradation from physical impact)
  • 4Internal CAN transceiver circuit fault in the IPB integrated brake control unit, software communication protocol mismatch, or damaged main control chip communication port.
  • 5Vehicle wading, cabin water ingress (e.g., leaks from a blocked sunroof drain hose), or high humidity corrodes the sensor connector and wiring harness, causing intermittent poor contact.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS1000/DiLink) to read the complete fault codes and freeze frame data. Verify if U043204 is a current fault and check associated fault codes (e.g., U012187, U043208, C003500) to aid troubleshooting.
  • 2
    Visually inspect the multi-axis acceleration sensor (usually located under the center console, beneath the center armrest, or under the front seats) for correct installation, external damage, and secure connector attachment. Verify there are no signs of physical impact.
  • 3
    Measure the sensor supply voltage (ignition ON; 5V ± 0.25V) and ground resistance (< 0.5Ω). Confirm the power supply is stable without fluctuation.
  • 4
    Check the CAN bus physical layer: Measure CAN-H (2.5-2.7V to ground) and CAN-L (2.3-2.5V to ground) voltages, and the bus termination resistance (power off, approximately 60Ω). Verify there are no short or open circuits.
  • 5
    Inspect the intermediate connector (especially terminal KJG05-18 and related pins) for backed-out pins, oxidation, or water ingress. If necessary, disassemble the connector, clean with electronic contact cleaner, blow dry, and apply conductive grease for protection.
  • 6
    Measure wiring harness continuity between the sensor and the IPB control unit (resistance less than 1 Ω) and insulation resistance (resistance to ground greater than 10 MΩ). Inspect for intermittent shorts or shorts to ground.
  • 7
    If all circuit measurements are normal, replace the multi-axis acceleration sensor assembly and use the diagnostic tool to perform the sensor zero-point calibration and initialization procedure (Enter IPB system → Special Functions → Sensor Calibration / G-Sensor Calibration).
  • 8
    Clear the fault code and perform a road test including straight-line driving, turning, hard acceleration, and hard braking. Confirm the ESP and AEB functions operate normally. Use the diagnostic tool to read the data stream and confirm the acceleration value is normal (close to 0m/s² when stationary). Verify the fault code does not recur.
Real-World Cases
BYD DTC AI Analysis

Song Pro multi-axis acceleration sensor connector oxidised, pins backed out

✓
While driving normally, the instrument panel suddenly displayed "Check ESP System" and "Check SRS System", with the ESP and airbag warning lights remaining on. The scan tool read DTCs U043204 and U012187 (lost communication with yaw rate sensor). Inspection revealed water ingress. Pin 18 of the multi-axis acceleration sensor connector (KJG05), located beneath the centre console, was oxidised and slightly backed out. Cleaned the terminals, repaired the backed-out pin, applied conductive grease, and recalibrated the sensor. Fault cleared.
Original source ↗
BYD DTC AI Analysis

Han EV Intermittent Multi-Axis Accelerometer Signal Abnormality

✓
Vehicle started normally from cold. After driving 7–10 km, the ESP warning light and automatic emergency braking limited warning illuminated. Cleared after restart. Retrieved DTCs U043204 and C003500 (acceleration sensor signal abnormal). Data stream showed abnormal lateral and longitudinal acceleration sensor values (reading -0.8 m/s² when stationary; normal should be near 0). Found the sensor connector loose with slight internal damage. Replaced the multi-axis acceleration sensor assembly, performed sensor calibration and steering wheel angle calibration. Fault fully resolved.
Original source ↗
BYD DTC AI Analysis

Tang DM airbag control module communication fault with U043204

✓
While driving, the vehicle suddenly displayed predictive collision warning and pedestrian detection system faults; EV mode unavailable. Read DTCs U043204, P1AC000 (airbag ECU collision warning), and U014000 (lost communication with BCM). Inspection found sunroof drain tube blocked, letting water into the cabin and soak the KJG05 connector, causing intermittent open circuit in the multi-axis acceleration sensor signal line. Cleaned the connector, cleared the drain tube, dried the wiring harness and waterproofed. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Qin Pro multi-axis accelerometer wiring harness chafed and shorted

✓
After driving over rough roads, the ESP and airbag warning lights illuminated and ESP failed at high speed. Retrieved DTCs U043204 and B190014 (sensor signal short to ground). The multi-axis acceleration sensor signal line showed 0Ω resistance to ground. Traced the wiring harness chafing through at the firewall grommet, causing the short. The sensor was also damaged. Repaired the harness, rerouted the wiring to prevent further chafing, replaced the sensor and performed the initialization procedure. Fault resolved.
Original source ↗
BYD DTC AI Analysis

Aftermarket audio installation caused CAN bus interference on Song MAX

✓
Aftermarket audio installation caused intermittent ESP and airbag fault warnings on the instrument cluster, occurring more frequently when the subwoofer was active. Codes U043204 (history) and U0021 (CAN bus open circuit) were logged. The audio power cable was running parallel to the main wiring harness, creating electromagnetic interference, and the amplifier ground point was improper, causing ground return interference. Rerouting the audio wiring (maintaining 15 cm or more separation from the main harness), relocating the ground connection to the designated body ground point, and installing ferrite cores on the sensor CAN lines resolved the issue. The faults have not returned.
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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.