AU
U007300

DTC U007300 indicates a communication failure or Bus-Off condition on the IPB (Intelligent Integrated Braking System / One-Box Integrated Braking System) private CAN bus — Atto 8

Braking System

DTC U007300 indicates a communication failure or Bus-Off condition on the IPB (Intelligent Integrated Braking System / One-Box Integrated Braking System) private CAN bus.

As the core control unit of the braking system, the IPB uses the private CAN bus (typically a 500 kbps high-speed CAN) to exchange real-time data with key modules such as the Vehicle Control Unit (VCU), Electronic Stability Control (ESC), Electronic Parking Brake (EPB), and Gateway Module (GWM).

This data includes safety-critical information such as wheel speed signals, brake pedal travel, brake force demand, and system status.

If the IPB detects its CAN controller has transmitted over 255 consecutive error frames, or detects continuous abnormal dominant or recessive bus levels, a terminating resistor mismatch, or severe signal integrity degradation, it triggers the Bus-Off protection mechanism, stores this DTC, and enters Limp Home mode.

The vehicle loses active safety functions such as ABS, ESC, and Automatic Emergency Braking (AEB), retaining only basic hydraulic braking capability.

This severe fault compromises driving safety (Severity Level 3).

The U007300 fault code on the Atto 8 indicates a high-severity communication failure on the IPB braking system private CAN bus. This can disable ABS, ESC, and AEB, leaving only basic braking. Common causes include a faulty IPB CAN transceiver or damaged CAN wiring/connectors, especially corrosion or poor contact at the IPB connector. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1Damage to the internal CAN transceiver (TJA1043 or equivalent chip) in the IPB control module or an abnormal power supply (3.3V/5V reference voltage drift) causes signal levels to deviate from the standard range (CAN-H: 2.5-3.5V, CAN-L: 1.5-2.5V).
  • 2Private CAN bus wiring harness physical layer fault: Vibration wear causing a short circuit between CAN-H and CAN-L, a short to ground, or an open circuit in the chassis wiring harness; or connector water ingress, oxidation, pin back-out, or excessive contact resistance (>5Ω), particularly at the 32-pin main IPB connector in the engine compartment.
  • 3Gateway controller routing function failure or CAN branch line fault between the IPB and the Gateway, preventing the IPB from establishing effective communication with the vehicle CAN network (Powertrain CAN/Body CAN).
  • 4Loose or oxidized ground wires on related control modules (such as the ESC or EPB), or corrosion at a shared ground point, cause ground potential drift and introduce common-mode interference, compromising CAN signal integrity (waveform distortion, excessive bit error rate).
  • 5Strong electromagnetic interference (such as from aftermarket 360-degree cameras, high-power audio amplifiers, or LED headlight drivers) coupling into the CAN wiring harness, or a vehicle collision damaging the CAN bus terminating resistor (120Ω) or causing an impedance mismatch.
What To Do
  • 1
    Fault freeze frame capture: Use the BYD dedicated diagnostic tool (VDS2000/VDS2100) to read the complete DTC snapshot data. Record parameters at the time of the fault, including vehicle speed, SOC, bus load rate, and IPB supply voltage. Check for accompanying related fault codes, such as U012200 (Lost Communication With ESC) and U014100 (Lost Communication With BCM).
  • 2
    Basic circuit check: Check the voltage drop of the IPB module constant power (B+), ignition switch power (IG1/IG2), and ground wires (G101/G102) (should be <0.5V). Check the continuity of fuses FB11 (10A), FB12 (15A), etc., and the contact condition of the fuse sockets to rule out a controller reset caused by momentary power interruption.
  • 3
    CAN bus physical layer check: Disconnect the IPB connector and use an oscilloscope to measure the private CAN waveforms (CAN-H to ground, CAN-L to ground). The normal static level is 2.5V; dynamic dominant levels are CAN-H ≈ 3.5V and CAN-L ≈ 1.5V. Use a multimeter to measure the termination resistance between CAN-H and CAN-L (should be approximately 60Ω, i.e., two 120Ω resistors in parallel). Measure the resistance to ground (should be >1MΩ to rule out a short circuit).
  • 4
    Harness continuity and insulation test: Measure the CAN line continuity resistance between the IPB connector, Gateway Controller (GWM), and ESC module (should be <1Ω). Measure the harness insulation resistance to the vehicle body (should be >10MΩ). Inspect for harness interference at sharp metal body edges in the engine compartment and at the rubber grommet where the chassis harness passes through the firewall.
  • 5
    Network isolation and module replacement: Use the half-split method to disconnect nodes on the private CAN network (ESC, EPB, GWM, etc.) and observe if the IPB resumes normal communication. If the bus recovers after disconnecting a specific node, inspect that node and the wiring harness between them. If the fault persists after disconnecting all nodes, replace the IPB module to verify.
  • 6
    Software flashing and configuration: After ruling out hardware faults, use the latest diagnostic software to flash program the IPB, GWM, and ESC. Check and correct the IPB CAN network configuration parameters (such as baud rate, terminal resistor enable bit, and message ID filter table).
  • 7
    Function verification and road test: Clear all DTCs, execute the IPB bleeding procedure (if replacing the hydraulic unit), perform a static pedal test (check the brake pedal travel sensor signal), and conduct a low-speed road test (20-40 km/h) to verify ABS activation and ESC intervention. Monitor continuously for 20 minutes to confirm U007300 does not recur.
Real-World Cases
BYD DTC AI Analysis

Seal 06 DM-i left domain controller CAN transceiver fault caused bus-off.

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Instrument cluster displayed powertrain fault and ESP system error; brake pedal went hard. Scanner retrieved DTC U007300 (CAN bus 1 OFF) along with multiple communication-loss codes including U012200 and U014100. Resistance between CAN-H and CAN-L at the diagnostic port measured only 12 Ω (critically low). Disconnecting the Left Domain Control Unit (engine bay) connector restored bus resistance to normal. This confirmed an internal CAN transceiver short in the Left Domain Control Unit; the controller continuously transmitted error frames, forcing the IPB private CAN bus into Bus-Off state. Replaced Left Domain Control Unit, performed online programming and immobiliser matching with the VDS tool, cleared DTCs and road-tested 30 km. Fault did not return.
Original source ↗
BYD DTC AI Analysis

Song PLUS DM-i IPB Private CAN Harness Connector Poor Contact Fault

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Customer reported intermittent ABS and ESC warning lights while driving, with a "Check brake system" message that sometimes cleared after restarting. Stored historic fault code U007300. Found water ingress in the IPB 32-pin main connector in the engine bay (BYD-32P-IPB); the connector lock was loose. The CAN-H pin (pin 15) showed black oxidation and had recessed 0.5 mm. Cleaned the connector with electrical contact cleaner, adjusted the pin for full insertion, applied conductive grease (DCA), and reassembled. Cable-tied the harness to prevent vibration. One-month follow-up confirmed no recurrence. This fault commonly occurs after driving through water in rainy season or after car washing.
BYD DTC AI Analysis

Poor Ground in Hybrid Vehicle Causes CAN Signal Interference

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The vehicle intermittently failed to start or suddenly lost power while driving, entering limp mode. The dashboard displayed "Check Power System" and "Check ESP". Fault codes read: U007300, U012200, and multiple VCU communication faults. Measured the CAN waveform at the OBD port and found numerous non-periodic spikes (noise). Inspection found the G101 ground bolt on the front bulkhead (shared ground for IPB and ESC) loose at 2 N·m (standard 9-11 N·m), with paint and oxidation on the surface. Sanded the ground point to bare metal, applied petroleum jelly for corrosion protection, and torqued the ground cable to specification. Reflashed the IPB and ESC control software to the latest version (Ver 3.2.1 or above, with optimized CAN anti-interference algorithm). Fault completely resolved.
BYD DTC AI Analysis

ESP module internal fault caused private CAN bus failure

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While driving, the ESP OFF and ABS warning lights suddenly illuminated and the steering became heavy. No communication with the ESP module. The IPB stored U007300 (CAN bus off) and U012200 (lost communication with ESP). Checked continuity of the private CAN wiring between IPB and ESP — normal; power and ground — normal. Disconnected the ESP module connector; IPB communication with other modules restored. Root cause: internal CAN transceiver failure in the ESP control unit, continuously occupying the bus or outputting dominant levels and causing bus-off. Replaced the ESP assembly (BYD policy typically requires replacing the IPB+ESC integrated assembly or the entire brake unit), performed yaw rate sensor calibration and ESC hydraulic bleed. Fault resolved.
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.