AU
U043208

DTC U043208 indicates a private CAN network communication fault in the IPB (Intelligent Power Brake) system — Atto 8

Braking System

DTC U043208 indicates a private CAN network communication fault in the IPB (Intelligent Power Brake) system.

Specifically, the IPB control unit detects an integrity check failure when receiving data frames from the MMx_TX module (Inertial Measurement Unit, IMU).

This fault involves data link layer errors, including received byte length mismatching the DBC definition (expected 8 bytes, actual length abnormal), Cyclic Redundancy Check (CRC) errors, Alive Counter discontinuity or abnormal jumps, and signal values exceeding the physically valid range (e.g., lateral acceleration >4g or yaw rate >300°/s).

The IMU provides vehicle lateral acceleration, longitudinal acceleration, and yaw rate signals, serving as the core sensor for ESC (Electronic Stability Control), ABS (Anti-lock Braking System), and AEB (Automatic Emergency Braking).

This fault prevents the IPB from obtaining accurate vehicle body attitude data and triggers the brake system degraded protection mode.

Symptoms include restricted ESC function, altered ABS intervention logic, or disabled Automatic Emergency Braking.

The system usually retains basic hydraulic braking functions.

The U043208 fault code on the Atto 8 indicates a private CAN communication fault between the IPB brake control unit and the IMU sensor. Severity is medium because ESC, ABS logic, or Automatic Emergency Braking may be restricted, while basic braking usually remains. Common causes include an internal IMU fault or damaged/loose CAN wiring or connectors. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1Inertial Measurement Unit (IMU) internal chip fault or firmware corruption, causing abnormal output data frame format or CRC calculation error.
  • 2Physical layer fault in the private CAN bus between the IPB and IMU, including loose connections, oxidized pins, damaged shielding causing electromagnetic interference (EMI), or terminating resistor deviation (typically 120Ω) causing signal reflection.
  • 3Outdated IPB Intelligent Power Braking control unit software or a faulty hardware CAN transceiver prevents correct parsing of the new IMU data protocol.
  • 4IMU sensor power supply fault: supply voltage is below 9V or above 16V, or ground circuit resistance is too high (>100mΩ), disrupting sensor operating timing.
  • 5After vehicle wading or a collision, a loose IMU mounting base or water ingress into the sensor causes the inertial sensing element (MEMS) to output abnormal electrical signals.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS2000/VDS2100) to read the complete fault code tree. Check for related faults such as U043204 (communication timeout) or C0035 (lateral acceleration sensor fault). Record the vehicle speed, yaw rate, and IMU raw signal status at the time of the fault from the freeze frame data.
  • 2
    Check the IMU installation status: Verify the IMU retaining bolt torque (typically 8-12 N·m), inspect the mounting surface for deformation, and verify the sensor level error is <2°. A mounting angle deviation causes the system to misinterpret the gravity component as lateral acceleration.
  • 3
    Measure the IMU power supply and ground: Disconnect the IMU connector, turn the ignition switch to ON, and measure the voltage from the power supply pin (usually Pin1/16) to ground. The standard value is 12V±0.5V. Measure the ground resistance; it must be <1Ω. Check the IPB main relay power supply stability.
  • 4
    Test the private CAN bus: Use an oscilloscope to measure the private CAN-H (orange/black) and CAN-L (orange/brown) waveforms between the IPB and IMU. Dominant levels must be 2.5-3.5V (CAN-H) and 1.5-2.5V (CAN-L), and the recessive level must be 2.5V. Measure the termination resistance; it must be approximately 60Ω (two 120Ω resistors in parallel). Check the wiring insulation; resistance to ground must be >1MΩ.
  • 5
    Perform IMU signal verification: With the vehicle stationary on a level surface, read the IMU data stream using the diagnostic tool. Lateral acceleration must be ≈0 m/s² (±0.2 m/s² tolerance), longitudinal acceleration must be ≈0 m/s², and yaw rate must be ≈0°/s. Slowly turn the steering wheel and verify the yaw rate signal changes smoothly without jumps or spikes.
  • 6
    Software update and calibration: If the wiring is normal, update the IPB control unit software to the latest version (verify the software number for the vehicle model); perform IMU zero-point calibration (Sensor Neutral Position Calibration) and yaw rate sensor calibration (Yaw Rate Sensor Calibration).
  • 7
    Component replacement and verification: If the fault persists, replace the IMU sensor (on some models, the IMU integrates into the IPB; replace the IPB assembly). After replacement, re-bleed the brake system and perform an ESC dynamic test (verify straight-line driving, turning, and emergency braking conditions).
Real-World Cases
BYD DTC AI Analysis

Song Plus DM-i IMU internal chip intermittently resets causing abnormal data frame length

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Vehicle: 2021 Song PLUS DM-i 110KM Flagship PLUS, 32,000 km. Symptoms: ESC and ABS warning lights illuminate intermittently. Lights clear after ignition restart. Frequency increases at high speed. Diagnosis: DTC U043208 (current). Freeze frame shows 118 km/h at time of fault; IMU status word 0x04 (data length error). IMU supply voltage 13.8 V (normal). Private CAN waveform analysis revealed abnormal 9-byte frames every 5–8 minutes (standard: 8 bytes). Disassembled IMU and found cold solder joint on the decoupling capacitor for the internal MEMS chip supply; chip was resetting sporadically and transmitting error frames. Resolution: Replaced IMU sensor (Part No.: HA2E-3636400), upgraded IPB software to 2023Q2, and performed yaw rate sensor calibration. Road tested 100 km; no recurrence.
BYD DTC AI Analysis

Seal EV: Abnormal private CAN bus termination resistance after accident repair

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Vehicle: 2022 Seal 700km Long Range RWD (rear-wheel drive), accident-repaired. Symptoms: After accident repairs, instrument cluster displayed "Brake System Fault" and automatic emergency braking was unavailable. Retrieved DTCs U043208 (historic fault) and U043204 (current fault). Diagnosis: Front compartment harness inspection found the IPB harness crushed in the accident. Water entered the 120Ω termination resistor connector at the private CAN bus branch, oxidizing the contact and drifting resistance to 85Ω; this caused signal reflection and bit errors. IMU tested normal, but IPB continuously received data frames with CRC errors. Solution: Repaired harness and replaced termination resistor (soldered to IMU harness end). Cleaned IPB and IMU connectors with alcohol and applied conductive grease. Bus resistance restored to 60Ω. Cleared DTCs and passed dynamic testing.
BYD DTC AI Analysis

Qin PLUS DM-i software version mismatch caused counter synchronisation failure

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Vehicle: 2023 Qin PLUS DM-i Champion Edition. Issue appeared after infotainment system upgrade. Symptoms: Day after OTA update to DiLink system, instrument cluster showed "Check Braking System" warning. Current DTC U043208. Diagnosis: Wiring check showed no damage. IMU power supply: 12.2V (normal). Technical bulletin confirms this batch has Alive Counter sync conflict between IPB software V1.02 and new IMU firmware. After 50 consecutive sleep/wake cycles, IPB counter validation logic fails against IMU. Solution: Replaced no hardware. Rolled back IPB software to V1.01, then upgraded to V1.03 patch. Performed 20 sleep/wake cycles; fault code did not return.
BYD DTC AI Analysis

Han EV Genesis Edition: Deformed IMU mounting base caused out-of-range signal values

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Vehicle: 2022 Han EV Genesis Edition 715KM front-wheel-drive flagship, repaired after underbody damage. Symptoms: Normal straight-line driving, but during fast cornering (>60 km/h) the ESC intervened abnormally. The instrument cluster showed a brake system fault; DTC U043208 (signal value error) stored. Diagnosis: The previous underbody impact had slightly deformed the subframe, twisting the IMU mounting bracket (located above the subframe) 2.3°. IMU data read normally at standstill, but cornering coupled gravitational acceleration components and pushed sensor output past the IPB’s 4.5g physical limit, triggering the signal value error. Resolution: Corrected the subframe mounting position, replaced the deformed IMU bracket, and recalibrated the IMU zero point. Road testing included a moose test; ESC operated normally and the fault cleared.
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.