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 — Seal U

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).

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Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Damaged internal CAN transceiver (TJA1043 or equivalent chip) in the IPB control module or 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, including: vibration wear on the chassis wiring harness causing a short circuit between CAN-H and CAN-L, a short to ground, or an open circuit; or connector water ingress and oxidation, terminal back-out, or excessive contact resistance (>5Ω) (especially at the 32-pin IPB main connector in the engine compartment).
  • 3Gateway controller routing function failure or a fault in the CAN branch line between the IPB and the gateway prevents 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 ESC or EPB), or a corroded shared ground point, causes ground potential drift and introduces common-mode interference, compromising CAN signal integrity (waveform distortion, excessively high bit error rate).
  • 5Strong electromagnetic interference (such as from aftermarket 360-degree surround-view 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 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) (must be < 0.5 V). Check the continuity of fuses FB11 (10 A), FB12 (15 A), etc., and socket contact conditions to rule out controller resets caused by momentary power interruptions.
  • 3
    CAN bus physical layer inspection: Disconnect the IPB connector. Use an oscilloscope to measure the private CAN waveforms (CAN-H to ground, CAN-L to ground). The normal static level is 2.5 V; dynamic dominant levels are CAN-H ≈ 3.5 V and CAN-L ≈ 1.5 V. Use a multimeter to measure the termination resistance between CAN-H and CAN-L (should be approximately 60 Ω, i.e., two 120 Ω resistors in parallel). Measure the resistance to ground (should be >1 MΩ 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-to-body insulation resistance (should be >10MΩ). Specifically inspect interference points between the engine compartment harness and sharp metal body edges, and 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 its connecting wiring harness. 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 (e.g., baud rate, terminal resistor enable bit, message ID filter table).
  • 7
    Functional 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), perform a low-speed (20-40 km/h) road test to verify ABS activation and ESC intervention, and 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 Seal U 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.