AU
U01000B

U01000B is a CAN communication fault code for BYD e-Platform 3 — Seal U

Braking System

U01000B is a CAN communication fault code for BYD e-Platform 3.0 models (such as the Seal 6 DM-i and Song PLUS DM-i).

This fault code indicates the IPB (Integrated Intelligent Braking System) detects a data integrity error when receiving the 0x240 message from the VCU (Vehicle Control Unit).

Specific errors include incorrect message byte length, CRC (Cyclic Redundancy Check) errors, non-continuous or abnormal Alive Counter jumps, or key signal values exceeding the valid range.

This powertrain CAN network communication fault may limit regenerative braking, cause abnormal electro-hydraulic braking coordination, and in severe cases, trigger the braking system degraded protection mode, compromising driving safety.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Poor contact, short circuit, or open circuit in the power CAN bus line between the VCU and IPB causes abnormal data frame transmission.
  • 2Outdated VCU software version or internal algorithm defect causing incorrect CRC calculation or abnormal counter logic in the generated 0x240 message.
  • 3IPB receiving module internal communication chip fault or software parsing error causing a false data corruption report.
  • 4Vehicle CAN network terminating resistor drift (not the standard 60Ω) or gateway routing delay causes data frame loss.
  • 5Voltage fluctuation in the 12V low-voltage power supply system (below 9V or above 16V) or electromagnetic interference causing communication signal distortion.
What To Do
  • 1
    Use the BYD VDS 1000/2000 diagnostic tool to perform a full system scan. Record the U01000B freeze frame data (including vehicle speed, voltage, and CAN signal status at the time of the fault) and any accompanying fault codes.
  • 2
    Check the power supply circuits (constant power B+, ignition power IG) and ground points G103/G104 for the VCU (located in the front compartment or cabin) and the IPB (located in the engine compartment near the brake master cylinder). Verify the voltage is stable at 12V±0.5V and the ground resistance is less than 1Ω.
  • 3
    Measure the voltage at pins 6 (CAN-H) and 14 (CAN-L) of the OBD diagnostic connector: CAN-H should be 2.5-3.5V and CAN-L should be 1.5-2.5V. Disconnect power and measure the terminal resistance. It should be approximately 60Ω (two 120Ω resistors in parallel). If abnormal, isolate the circuit and measure the terminal resistance of the VCU and IPB separately.
  • 4
    Inspect the VCU to IPB CAN harness connectors (especially the front compartment harness junction and IPB connector) for backed-out pins, corrosion, water ingress, or poor contact. Perform continuity and insulation tests if necessary.
  • 5
    Perform a CAN bus physical layer test: Use an oscilloscope to observe the CAN waveform and check for signal reflection, abnormal bit timing, or noise interference. Simultaneously, verify proper grounding of the nearby high-voltage wiring harness shield.
  • 6
    Compare the VCU and IPB software versions against the BYD technical bulletin. If a communication optimization program is available, update the software (battery charge must be above 30% with the ignition switch in the ON position).
  • 7
    If wiring and software are normal, use the substitution method: first replace the VCU, clear the fault code, and perform a road test (apply the brakes at least 50 times). If the fault recurs, replace the IPB assembly.
  • 8
    After replacing the IPB, perform the following: brake line bleeding, ESC sensor calibration, longitudinal acceleration sensor calibration, and CAN signal handshake learning between the VCU and IPB.
Real-World Cases
BYD DTC AI Analysis

Intermittent brake system warning light on Seal 6 DM-i instrument cluster

✓
A 2024 Seal 6 DM-i with 8,500 km. The owner reported the brake system warning light occasionally illuminating on the instrument cluster with the message "Please check brake system". VDS scan revealed the IPB system stored DTCs U01000B (FM Data Corruption 6) and U010087 (VCU Communication Timeout). Freeze frame data showed the fault occurred at approximately 60 km/h. Checked the CAN wiring harness between the VCU and IPB; found a retaining clip detached at the left front chassis rail. The harness had chafed against a sharp body edge, damaging the CAN-H wire insulation and causing an intermittent short. Repaired the harness and resecured it; fault resolved.
Original source ↗
BYD DTC AI Analysis

Song PLUS DM-i Stiff Brake Pedal Fault

✓
While driving, a 2021 Song PLUS DM-i suddenly displayed "Brake System Fault" and "ESP Fault" on the instrument cluster, and the brake pedal became hard. VDS showed IPB codes U01000B and C123456 (hydraulic unit fault). Inspection found outdated VCU software (early versions have a 0x240 message counter jump defect) and oxidation on IPB ground wire G104. Cleaned the ground connection and upgraded the VCU to the latest software version (Ver 3.2.1). The fault has not returned.
Original source ↗
BYD DTC AI Analysis

Dolphin unable to enter OK mode and reports communication fault.

✓
A 2023 Dolphin failed to enter Ready mode after being parked overnight, with the instrument cluster showing multiple system faults. VDS scanning revealed the IPB, BMS, and MCU all reported communication faults with the VCU; the IPB logged U01000B. CAN bus voltage measurement showed CAN-H shorted to ground (0.2V). Sectional troubleshooting isolated water ingress in the VCU connector from high-pressure washer spray during cleaning, causing corrosion and a short in the CAN-H pin. Cleaned and dried the VCU connector, confirmed normal insulation, and resolved the fault. Check engine bay sealing.
Original source ↗
BYD DTC AI Analysis

Seal EV loss of power while driving with brake warning

✓
A 2022 Seal EV experienced intermittent power loss during high-speed driving. The dashboard displayed "Check connector" and "Braking system fault" warnings. VDS retrieved IPB history DTC U01000B (FM data corruption 6). Checking the VCU power supply found burnt contacts on the IG1 ignition relay, causing the VCU to intermittently lose power and restart. The 0x240 message sent during the restart was incomplete. Replaced the IG1 relay in the engine bay fuse box and inspected the VCU power management module. Fault resolved.
Original source ↗
BYD DTC AI Analysis

Song Pro DM-i sets data corruption fault after IPB replacement

✓
A 2022 Song Pro DM-i had its IPB assembly replaced due to brake noise. Post-repair, VDS scanning showed DTC U01000B (FM data corruption 6) that would not clear. Inspection revealed the replacement IPB (part number SC2E-3550100, low-spec version) was incompatible with the original SC2E-3550100A (high-spec with ACC), causing CAN message parsing errors. After installing the correct IPB and performing online configuration and sensor calibration, the fault codes cleared and brake system operation returned to normal.
Original source ↗
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.