AU
C059400

DTC C059400 indicates a functional fault in the brake booster motor within the IPB (Intelligent Power Brake) system — Atto 3

Braking System

DTC C059400 indicates a functional fault in the brake booster motor within the IPB (Intelligent Power Brake) system.

This brushless DC motor integrates into the IPB electro-hydraulic module to replace the traditional vacuum booster.

It provides electric brake assist based on pedal input and coordinates energy recovery.

The IPB control unit sets this code upon detecting abnormal motor current, abnormal speed feedback, a drive circuit fault, or motor mechanical binding.

This fault causes a hard brake pedal, reduced brake assist, and increased braking distance.

It also degrades or disables functions including ABS, ESC, and Automatic Emergency Braking, severely compromising driving safety.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Internal damage to the IPB brake booster motor: worn motor bearings, seized rotor, or demagnetized permanent magnets, causing abnormal motor operation or abnormal current draw.
  • 2Motor drive circuit fault: Damage to the MOSFET, gate driver chip, or sampling resistor in the IPB internal H-bridge drive circuit causes an abnormal motor drive signal.
  • 3Abnormal power supply: Poor contact in the IPB module terminal 30 constant power or terminal 31 ground circuit, loose fuse connection, or voltage fluctuation (below 9V or above 16V), causing unstable motor power supply.
  • 4Motor position sensor fault: An abnormal signal from the Hall sensor or resolver integrated into the motor prevents the control unit from accurately identifying the motor rotor position.
  • 5Control software or calibration data fault: Internal software bug in the IPB control unit, corrupted calibration data, or outdated version causes incorrect assessment of motor status.
What To Do
  • 1
    Use the dedicated diagnostic tool (VDS2000/3000) to read the complete fault codes and freeze frame data. Check specifically for accompanying fault codes such as C059100 (motor voltage too low), C059500 (internal drive fault), or C003700 (pump motor fault). Record parameters such as vehicle speed and pedal travel when the fault occurred.
  • 2
    Visually inspect the IPB electro-hydraulic module exterior for damage, fluid leakage, or burn marks. Check the master cylinder connection and wiring harness connectors (especially the large 30pin connector) for looseness, water ingress, or corrosion. Measure the voltage between the power supply (Pin30) and ground (Pin31) to verify it is within 12V±0.5V.
  • 3
    Perform the IPB function self-test: Use the diagnostic tool to run the brake booster motor drive test. Listen for normal motor operation (expect an even running sound without binding). Observe if the brake pedal sinks automatically. Simultaneously measure the motor operating current using a current clamp (normal value is typically 5-15A; abnormal values may exceed 25A or approach 0A).
  • 4
    Inspect the brake system hydraulic circuit: verify the brake fluid level is normal and the lines are leak-free to rule out indirect faults caused by excessive hydraulic resistance overloading the motor.
  • 5
    Software check and upgrade: Verify the IPB control unit software version and compare it with the BYD Technical Service Bulletin (TSB). If an optimized software version is available for this fault code, perform an online programming upgrade. If necessary, perform IPB recalibration and zero-point learning.
  • 6
    If the above checks are normal but the fault persists, this indicates a hardware fault in the IPB internal motor or drive circuit. Replace the IPB electro-hydraulic module assembly (verify the part number matches the vehicle configuration). After replacement, perform new module programming, brake system bleeding (use the diagnostic tool to run the bleeding procedure), and ESC calibration.
Real-World Cases
BYD DTC AI Analysis

Song Plus DM-i: IPB motor jamming causes stiff brake pedal

✓
Vehicle had covered 30,000 km. After a cold start one morning, the dashboard displayed "Brake System Fault" with DTC C059400 stored. The driver reported the brake pedal had gone noticeably hard, requiring heavy pedal effort to slow the vehicle. Visual inspection of the IPB module showed no external damage. During the motor drive test, a clicking sound came from inside but the motor did not turn. Disassembling the IPB revealed the internal assist motor bearing had corroded and seized (the vehicle had previously waded through water). Replaced the IPB assembly and performed the brake bleed procedure to clear the fault.
BYD DTC AI Analysis

Loose ground wire caused intermittent C059400 fault

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ABS/ESC warning light occasionally illuminated when driving over speed bumps or rough roads. Scan tool retrieved intermittent DTC C059400. While checking IPB supply voltage, found the left engine bay ground point (G101) bolt loose. This caused excessive IPB ground resistance (measured 2.3Ω; normal is <0.1Ω). Poor grounding during bumps caused momentary voltage loss to the motor drive. Tightened the ground point and applied conductive paste. Road-tested 50 km continuously — fault did not recur.
BYD DTC AI Analysis

Outdated software caused a false brake booster motor fault.

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Vehicle had 1000 km when it suddenly threw a braking system fault at highway speed: DTC C059400. Checked motor and wiring harness—both normal. Voltage stable at 12.4V. Tech bulletin search revealed IPB software V1.02.03 on this batch has a bug: motor current sampling threshold set too tight, causing false triggers during rapid deceleration when switching between regen and mechanical braking. Flashed IPB to V1.03.05. Fault cleared, no recurrence after one month of monitoring.
BYD DTC AI Analysis

Brake fluid replaced without bleeding, causing motor overload damage

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The vehicle developed a C059400 fault after brake fluid replacement at a non-authorised workshop. Investigation revealed the technician used the traditional foot-pumping method to bleed the brakes rather than performing the IPB active bleed procedure with a diagnostic tool. Air entered the wheel cylinders, causing the IPB motor to run under high load for an extended period while attempting to build pressure, eventually overheating and failing. Motor winding resistance measured open circuit (normal approximately 1.5Ω). Replaced the IPB module and correctly performed the diagnostic tool bleed procedure to resolve.
BYD DTC AI Analysis

Burnt IPB driver chip caused motor failure

✓
Vehicle failed to power up (READY light off) with multiple brake system fault codes present, primary code C059400. IPB power supply tested normal, but the scan tool could not drive the motor. Opened the IPB control unit board and found visible burn marks on the H-bridge driver chip (typically INFINEON or NXP), along with characteristics of a motor winding short. Determined that motor insulation aging caused a short circuit, overloading and burning out the driver chip. Replaced the IPB assembly (motor and drive board integrated); fault resolved.
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.