AU
C059000

This DTC indicates the IPB (Intelligent Power Brake) electro-hydraulic control module detects the brake booster motor drive circuit supply voltage exceeds the calibrated threshold (typically >16V) — Seal U

Braking System

This DTC indicates the IPB (Intelligent Power Brake) electro-hydraulic control module detects the brake booster motor drive circuit supply voltage exceeds the calibrated threshold (typically >16V).

In BYD DMi models, the 12V low-voltage system powers the IPB, which uses motor direct-drive brake assist (without a vacuum booster).

Faults in the DC-DC converter, generator, or IPB internal power management circuit causing voltage increases trigger this DTC.

Continuous overvoltage can overheat and damage the IPB internal MOSFETs or motor driver chip.

This triggers system protection mode, resulting in a hard brake pedal, reduced brake assist, or restricted ABS/ESC functions.

Severe cases force the vehicle into limp mode.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1DC-DC converter fault: High-voltage to 12V DC-DC module failure abnormally increases output voltage (>15-16V), causing the IPB supply voltage to exceed limits.
  • 2IPB electro-hydraulic module internal fault: A fault in the IPB internal power regulation circuit, voltage sampling circuit, or motor drive circuit causes actual overvoltage or a false overvoltage report.
  • 312V charging system fault: On DMi models, generator regulator fault or abnormal DC-DC control strategy causes overvoltage charging in the low-voltage system.
  • 4Wiring harness short circuit or cross-circuit: Abnormal contact between the brake booster motor power wire and the high-voltage harness, or short circuit to another high-voltage source.
  • 5Faulty battery or poor grounding: Excessive battery internal resistance, aging, or poor grounding causes abnormal voltage fluctuations, triggering sampling circuit protection.
What To Do
  • 1
    Fault confirmation and data reading: Use VDS2000/3000 to read all DTCs, freeze frame data (record the actual voltage when the fault occurred), and the live data stream. Verify if the actual IPB supply voltage remains above 16V.
  • 2
    Low-voltage system voltage check: Measure the 12V battery static voltage (normal 12.4–12.8V) and dynamic voltage (during start-up/charging, normal 13.5–14.8V, must not exceed 15.5V). Check for overvoltage.
  • 3
    DC-DC output check: With the vehicle in READY mode, measure the voltage at the DC-DC converter output terminal and the waveform to ground. If the output voltage is >15.5V or the waveform is abnormal, replace the DC-DC converter assembly.
  • 4
    IPB circuit inspection: Check the continuity (<1 Ω) and insulation resistance (>10 MΩ) of the IPB module power wires (constant B+, IGN power) and ground wiring harness. Check for burnt, backed-out, or corroded connector terminals.
  • 5
    IPB module diagnosis and replacement: If the external supply voltage is normal (13.5-14.8V) but the IPB still reports C059000, first flash the IPB software (if an updated version is available). If the fault persists, replace the IPB electro-hydraulic module assembly, and perform brake system bleeding, calibration, and ESC matching.
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i DC-DC Output Overvoltage Causing C059000

✓
While driving normally, the ABS and ESC warning lights suddenly came on and the instrument cluster displayed "Brake system fault". Retrieved DTCs C059000 (Brake booster motor voltage too high) and U029D00 (Lost communication with DC-DC). Measured battery voltage at 17.2 V at idle; freeze frame showed 16.8 V when the fault occurred. Found the DC-DC converter's internal regulation circuit damaged. Replaced the DC-DC assembly and voltage returned to normal. Cleared the codes and C059000 has not returned.
BYD DTC AI Analysis

Faulty IPB internal sampling circuit falsely reporting overvoltage

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The vehicle drove normally, but the brake system warning light came on intermittently. The scanner showed only active DTC C059000. Live data showed IPB supply voltage at 14.2V (normal), but internal sampling values read 18.5V. I checked external wiring and the DC-DC converter and found no faults. Diagnosed as IPB internal ADC sampling circuit or voltage divider resistor failure causing false readings. I replaced the IPB electro-hydraulic module and performed calibration; fault cleared.
BYD DTC AI Analysis

Wiring harness wear caused stray voltage to enter the IPB power supply.

✓
Post-accident repair, a Song PLUS DMi repeatedly set alternating codes C059000 and C059100 (low voltage). Inspection found the front compartment harness damaged in the collision: the IPB constant-power wire and HV interlock harness had insulation damage and were contacting. With the HV system active, abnormal voltage leaked into the IPB power circuit through the damage. Repaired the harness insulation, separated HV and LV wiring routes, and replaced the damaged fuse and connectors. Fault resolved.
BYD DTC AI Analysis

Generator regulator failure caused hybrid mode overvoltage

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Vehicle logged DTC C059000 in HEV mode; EV mode was normal. Diagnosis found overvoltage (16.5V) only when the engine was generating. Voltage at the generator output fluctuated. Generator disassembly revealed a damaged regulator, causing unregulated charging voltage. Replaced the generator assembly. System voltage stabilized at 14.2V and the fault code did not return.
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.