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) — Seal U

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.

The U043204 fault code on the Seal U indicates a medium-severity communication timeout between the IPB braking control unit and the multi-axis acceleration sensor. This can limit ESP, AEB, brake force distribution, or energy recovery, though basic braking usually remains. Common causes include a faulty sensor power or ground circuit, or damaged/corroded CAN wiring and connectors. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Multi-axis acceleration sensor (MMx) power supply circuit fault (5V reference voltage abnormal or missing) or poor ground connection, causing the sensor to fail to initialize normally or operate continuously.
  • 2Physical damage, open circuit, or short circuit in the CAN bus communication wiring; or excessive contact resistance in key intermediate connectors (e.g., KJG05, BJA01) due to backed-out pins, oxidation, or water corrosion.
  • 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., leakage from a blocked sunroof drain hose), or high-humidity environments corrode the sensor connector and wiring harness, causing intermittent poor contact.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS1000/DiLink) to read all fault codes and freeze frame data. Confirm if U043204 is a current fault and check associated fault codes (e.g., U012187, U043208, C003500) to assist with fault isolation.
  • 2
    Visually inspect the multi-axis acceleration sensor (usually located under the centre console, at the bottom of the centre armrest box, or under the front seats) for proper installation, external damage, and secure connector engagement. Verify 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 is no short or open circuit.
  • 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 it with electrical contact cleaner, blow dry, and apply conductive grease for protection.
  • 6
    Measure the wiring harness between the sensor and the IPB control unit for continuity (resistance less than 1 Ω) and insulation (resistance to ground greater than 10 MΩ). 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 procedures (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 using the diagnostic tool to 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 Seal U Fault Codes
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.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.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.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.