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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
Real-World Cases
BYD DTC AI Analysis

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

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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Outdated software caused a false brake booster motor fault.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

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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
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
Data confidence: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.