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) — Qin Plus

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 — Qin Plus
  • 1Multi-axis acceleration sensor (MMx) power supply circuit fault (5V reference voltage abnormal or missing) or poor ground point connection, preventing the sensor from initializing properly or operating continuously.
  • 2Physical damage, open circuit, or short circuit in CAN bus communication lines; or excessive contact resistance in key intermediate connectors (e.g., KJG05, BJA01) due to backed-out pins, oxidation, or water ingress.
  • 3Multi-axis acceleration sensor damage (internal MEMS chip failure, cold solder joint, moisture ingress from seal failure, or performance degradation due to 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., leaking from a blocked sunroof drain tube), or high-humidity environments cause corrosion of the sensor connector or wiring harness, resulting in intermittent poor contact.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS1000/DiLink) to read all fault codes and freeze frame data. Verify if U043204 is a current fault and check for related fault codes (e.g., U012187, U043208, C003500) to help isolate the fault.
  • 2
    Visually inspect the multi-axis acceleration sensor (usually located under the center console, at the bottom of the center armrest box, or under the front seats) for proper mounting, external damage, and secure connector engagement. Confirm 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 voltage (2.5–2.7 V to ground), CAN-L voltage (2.3–2.5 V to ground), and bus termination resistance (measure with power off, approximately 60 Ω). Confirm 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 the continuity (resistance should be less than 1 Ω) and insulation resistance (resistance to ground should be greater than 10 MΩ) of the wiring harness between the sensor and the IPB control unit. Check for intermittent short circuits 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, hard braking, and other driving conditions). Verify ESP and AEB functions operate normally. Read the data stream using the diagnostic tool to confirm the acceleration value is normal (close to 0 m/s² when stationary) and the fault code does not return.
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 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.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.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.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
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.