AU
U01000C

DTC U01000C indicates a power CAN bus communication timeout between the IPB (Integrated Intelligent Braking System) and the Front Motor Controller (FMC) — Atto 3

Braking System

DTC U01000C indicates a power CAN bus communication timeout between the IPB (Integrated Intelligent Braking System) and the Front Motor Controller (FMC).

Timeout 6 specifically refers to the loss of a specific cyclic message, typically the 0x240 network management message.

As the main braking control unit, the IPB requires real-time front motor speed, torque, and temperature data to coordinate the seamless transition between motor regenerative braking and hydraulic mechanical braking.

If the communication interruption exceeds the set threshold (typically >100ms), the IPB triggers this fault and enters a degraded mode.

This mode disables regenerative braking and may restrict ESC/ABS to basic functions; however, conventional hydraulic braking remains available.

This network communication fault may result from an offline Front Motor Controller, a CAN bus physical layer anomaly, or an IPB receiver module failure.

The U01000C fault code on the Atto 3 indicates a power CAN bus communication timeout between the Integrated Intelligent Braking System and the Front Motor Controller. Severity is medium: normal hydraulic braking should remain, but regenerative braking and some ESC/ABS functions may be limited. Common causes include a Front Motor Controller power or wake-up fault, or CAN wiring/termination issues. 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 3
  • 1Front motor controller (MCU) low-voltage power supply fault: including a blown 12V constant power fuse (e.g., F1/14), missing IGN wake-up signal, or open high-voltage interlock circuit causing the controller to enter sleep mode.
  • 2CAN bus physical layer fault: Short circuit between CAN-H and CAN-L, short to ground/power, or open circuit in the lines between the IPB and front motor; or terminating resistor drift (standard value 60Ω, measured value outside the 40-80Ω range).
  • 3Front motor controller internal fault: damaged CAN transceiver chip, main control MCU crash, or software infinite loop preventing periodic transmission of the 0x240 status message.
  • 4Poor wiring harness connector contact: The CAN harness connector in the front high-voltage compartment or at the firewall is loose, oxidized from water ingress, or has backed-out pins, or poor shield grounding causes signal interference.
  • 5IPB integrated brake unit fault: damaged internal CAN receiver module, gateway routing table error, or software version mismatch (e.g., IPB software version incompatible with MCU).
What To Do
  • 1
    Initial diagnostic scan: Read the complete DTC snapshot using VDS2000/3000. Confirm if U01000C is a current or historical fault. Check for accompanying network faults, such as U0101 (TCU communication fault). Record the vehicle speed and bus load rate at the time of the fault.
  • 2
    Power supply system troubleshooting: Measure the voltage at pin BXX-XX (constant power BAT) on the front motor controller low-voltage connector; it should be 12V ± 0.5V. During startup, the voltage at pin BXX-XX (IGN wake-up) should be >11V. Check the continuity of fuses F1/14, F2/03, etc., in the engine compartment fuse box, and verify the relay engagement status.
  • 3
    CAN bus voltage check: Turn ignition switch to ON. Measure voltage from diagnostic connector pin 6 (CAN-H) to ground (2.5-3.5 V) and pin 14 (CAN-L) to ground (1.5-2.5 V). The difference is approximately 2 V. If voltage is abnormal, measure the wiring harness between the IPB and front motor in sections.
  • 4
    Terminal resistance and continuity test: Power off the vehicle. Measure the resistance between diagnostic socket pins 6 and 14. Normal resistance is approximately 60Ω (two 120Ω terminating resistors in parallel). Disconnect the front motor connector in the motor compartment and the IPB connector in the cabin. Measure the CAN wiring harness continuity resistance between the two connectors; resistance must be <1Ω. Insulation resistance to ground must be >10MΩ.
  • 5
    Module replacement and software flashing: Flash the front motor controller with the latest software version (to fix potential communication freeze bugs). If ineffective, swap the front motor controller for testing. If the fault transfers, replace the front motor controller. If the code persists, replace and program the IPB assembly.
  • 6
    System calibration and verification: After repair, clear the DTC. Perform the IPB hydraulic system bleeding procedure, ESC yaw rate sensor calibration, and brake pedal position sensor learning. Road test the vehicle to verify regenerative braking function recovery and ensure the fault code does not return.
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i front motor CAN harness chafed through, causing intermittent communication interruption

✓
When driving over rough roads, the dashboard intermittently displayed 'Brake System Fault' with active DTC U01000C. Checked the front motor controller power supply and ground – normal. Measured CAN bus static voltage – normal. However, resistance jumped when wiggling the wiring harness. Found the CAN harness at the left front longitudinal rail had chafed through against the body sheet metal, exposing copper wires and causing an intermittent short to ground. Repaired the harness and applied chafe protection. Fault resolved.
BYD DTC AI Analysis

Song Pro DM: Poor Contact in Front Motor Controller Fuse Causes Communication Timeout

✓
At cold start, the IPB system set DTC U01000C; the code cleared after warm-up. Measuring the front motor controller 12V supply revealed voltage fluctuating between 10–14V. Inspection of the engine compartment fuse box found the F1/14 fuse socket (front motor power supply) loose with 3Ω contact resistance. Replaced the fuse base and tightened the terminals; supply voltage stabilized above 12.4V, eliminating the fault.
BYD DTC AI Analysis

IPB software version mismatch causes message parsing failure on Qin PLUS DM-i

✓
Replaced the front motor controller, but DTC U01000C kept returning. Circuit measurements showed no faults. The scan tool revealed IPB software version V1.02 and front motor software version V2.10—a version mismatch. Flashed the IPB software to V2.10, restoring normal communication. This case shows that after replacing components, ensure software version compatibility across all nodes on the CAN network.
BYD DTC AI Analysis

Tang DM front motor controller internal CAN transceiver damaged

✓
Vehicle failed to engage high voltage. Both IPB and VCU reported communication timeouts with the front motor. CAN bus termination resistance at the front motor end measured 120Ω (normal), but oscilloscope testing showed the front motor sent no CAN messages. Disassembling the front motor controller revealed the internal CAN transceiver chip TJA1043 had burned out (likely from a high-voltage surge). Replaced the front motor controller assembly; fault cleared.
Other Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.
Common problems reported for Atto 3 →Atto 3 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.