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 8

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 8
  • 1Multi-axis acceleration sensor (MMx) power supply circuit fault (5V reference voltage abnormal or missing) or poor ground point connection, causing the sensor to fail to initialize normally or operate continuously.
  • 2Physical damage, open or short circuit in the CAN bus communication lines, or backed-out pins, oxidation, or corrosion from water ingress in key intermediate connectors (e.g., KJG05, BJA01) causing excessive contact resistance.
  • 3Multi-axis acceleration sensor damaged (internal MEMS chip failure, 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 (such as leaks from a blocked sunroof drain tube), or high-humidity environments cause sensor connector and wiring harness corrosion, resulting in intermittent poor contact.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS1000/DiLink) to read complete fault codes and freeze frame data. Verify if U043204 is a current fault and check related fault codes (e.g., U012187, U043208, C003500) to assist fault isolation.
  • 2
    Visually inspect the multi-axis acceleration sensor (usually located under the center console, at the bottom of the center armrest, or under the front seats) for mounting condition, external damage, and connector connection. Confirm 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 the CAN-H (2.5-2.7V to ground) and CAN-L (2.3-2.5V to ground) voltages, and the bus termination resistance (measure with power off, approximately 60Ω). Confirm there are no short or open circuits.
  • 5
    Inspect the intermediate connector (especially terminal KJG05-18 and related pins) for backed-out terminals, oxidation, or water ingress. If necessary, disassemble the connector, clean with electrical contact cleaner, blow dry, and apply conductive grease for protection.
  • 6
    Measure the continuity (resistance should be less than 1 Ω) and insulation (resistance to ground should be greater than 10 MΩ) of the wiring harness between the sensor and the IPB control unit. Inspect for intermittent short circuits or shorts to ground.
  • 7
    If all circuit measurements are normal, replace the multi-axis acceleration sensor assembly. 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 ESP and AEB functions operate normally. Read the data stream with the diagnostic tool to confirm the acceleration value is normal (close to 0m/s² when stationary) and 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 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.