AU
P056300

DTC P056300 indicates the IPB (Intelligent Power Brake) ECU detects its 12V supply voltage exceeds the system-calibrated safety threshold (typically 16V-18V, depending on vehicle calibration) — Seal U

Braking System

DTC P056300 indicates the IPB (Intelligent Power Brake) ECU detects its 12V supply voltage exceeds the system-calibrated safety threshold (typically 16V-18V, depending on vehicle calibration).

In BYD DM-i and other new energy vehicles, the IPB system integrates electro-hydraulic brake assist, ESC, ABS, and automatic emergency braking.

This fault means the IPB module detects an abnormally high input voltage, which can damage internal solenoid valve coils, motor drive circuits, or sensors.

As a result, the system stores the fault code and may enter a degraded protection mode, limiting or disabling ESC/ABS functions.

This causes a hard brake pedal and increased braking distance, severely compromising driving safety.

Distinguish this code from engine management system DTC P0563: DTC P056300 applies specifically to the IPB system.

Typical causes include abnormal DC-DC converter output, IPB internal voltage monitoring circuit faults, or poor circuit grounding.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1DC-DC converter voltage regulation failure: In DM-i models, the DC-DC converter converts the high-voltage battery output to 12V low voltage. If the internal regulation circuit fails, the output voltage may exceed 15V or even rise above 16V, causing the IPB to report an overvoltage fault.
  • 2IPB electro-hydraulic module internal fault: The voltage monitoring circuit (A/D converter) inside the IPB ECU drifts or fails, causing it to falsely report high voltage while the actual measured external voltage is normal.
  • 3Abnormal contact resistance in the power supply circuit: IPB power wiring harness connectors (such as plugs A03 and B02) are loose, oxidized, or making poor contact, or ground points (G101, G102, etc.) are corroded or insufficiently tightened. This causes the reference ground potential to drift and the ECU to detect a relative voltage increase.
  • 412V battery internal resistance too high: Battery aging or sulfation increases internal resistance. During charging, the terminal voltage rises rapidly, exceeding the IPB monitoring threshold.
  • 5Charging and Power Distribution Assembly fault: On some models, a faulty internal DC-DC control unit causes an uncontrolled increase in output voltage.
What To Do
  • 1
    Read freeze frame data: Use a VDS2000 or Launch X-431 diagnostic tool to read the DTC freeze frame. Record the specific voltage (Voltage_Battery_Value), vehicle speed, time, and system status when the fault occurred to determine whether the fault is persistent or intermittent.
  • 2
    Measure high and low-voltage system voltages: With the vehicle in the Ready state, use a multimeter to measure the voltage across the battery positive and negative terminals (normal: 13.5-14.5V). Simultaneously read the actual IPB supply voltage (IPB_Voltage) in the VDS data stream. Compare the two values to check for a circuit voltage drop or monitoring error.
  • 3
    Check the DC-DC output characteristics: Connect an oscilloscope to monitor the DC-DC output waveform and check for voltage spikes or excessive ripple. If the DC-DC output continuously exceeds 15.5V, check the charging and power distribution assembly or the DC-DC converter. Swap components for testing if necessary.
  • 4
    Check the IPB power supply circuit: disconnect the IPB wiring harness connector and inspect terminals A03 (constant power), A04 (ignition power), and others for oxidation or backed-out pins; measure the voltage drop of the power supply circuit from the battery to the IPB (must be less than 0.2V); check the tightness of the IPB housing ground point and the battery negative ground point (standard torque is typically 8-10 N·m); sand any corroded ground points.
  • 5
    IPB system self-check and calibration: After restoring the power supply, clear the fault code, bleed the IPB system, calibrate the sensors (steering angle sensor and pressure sensor), and perform a function test. If the fault persists and the measured voltage is normal, replace the IPB electro-hydraulic brake assembly.
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i charging and power distribution assembly fault caused the braking system to log P056300

✓
A 2021 Song Plus DM-i with 23,000 km displayed "Brake System Fault" and "ABS Fault" warnings. VDS read DTC P056300 (System Voltage Too High) and multiple IPB communication faults. Voltage at the DC output terminal fluctuated between 13.8 V and 16.2 V, well outside the normal range. The DC output wiring, ground connections, and fuses showed no abnormalities. Replacing the charging/distribution assembly stabilized voltage at 14.2 V, cleared the fault codes, and restored the brake system to normal. The cause was an internal DC-DC control circuit failure in the charging/distribution assembly, which caused loss of output voltage regulation.
Original source ↗
BYD DTC AI Analysis

BYD E5: IPB Power Supply Circuit Poor Contact Causing Voltage Anomaly

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Dashboard ESC warning light on. Retrieved DTC P056300. Battery voltage measured 12.4V (normal). Inspecting the IPB wiring harness connector revealed oxidised and burnt terminals inside the A03 power plug, causing high contact resistance. During vehicle operation, poor contact generated voltage fluctuations and the IPB ECU detected transient overvoltage. Sanded earth point G101, replaced the IPB power harness connector, retightened the battery negative earth bolt, cleared the fault codes. Fault resolved.
Original source ↗
BYD DTC AI Analysis

Tang DM-i DC-DC output fault caused overvoltage warnings in multiple systems

✓
The charging gun tripped during DC fast charging. The dashboard displayed "Low Voltage Power Supply System Fault" and "Braking System Fault". VDS scan revealed P056300 and voltage-related faults in IPB, ESP, EPS, and other systems. Live data from the low-voltage battery manager showed system voltage at 16.8V, with charge/discharge status flickering between "Charging" and "Discharging". DC-DC output voltage measured above 16.5V. Diagnosed as faulty DC-DC regulator inside the charging and power distribution assembly. Replaced the charging and power distribution assembly. System voltage restored to 14.1V, all system fault codes cleared, and normal fast charging operation restored.
Original source ↗
BYD DTC AI Analysis

Song Pro DM-i IPB Internal Voltage Monitoring Circuit Fault

✓
No accident history. The "Check Brake System" warning appeared intermittently during normal driving. VDS showed intermittent fault code P056300. Freeze frame data indicated 17.1V when the fault occurred, but real-time measurements showed both the battery and DC-DC output at a normal 14.0V. Inspected the IPB power supply wiring, ground points, and harness connectors—no faults found. Diagnosis: drift or damage to the IPB ECU internal voltage sampling circuit (A/D converter), causing false high-voltage warnings. Replaced the IPB electro-hydraulic brake assembly (part number SC-EE-3610100). Monitored continuously for one week; the fault has not returned.
BYD DTC AI Analysis

Qin PLUS DM-i 12V battery aging caused charging overvoltage

✓
Vehicle: 3 years old, 50,000 km. Dashboard displayed braking system fault. Scan found active DTC P056300. Battery voltage measured at 15.8V immediately after startup. IPB data stream showed voltage rising simultaneously. DC-DC converter tested normal. Battery internal resistance measured 18mΩ (normal <8mΩ). Determined aged battery with high internal resistance forced DC-DC to raise output voltage to maintain charging current, triggering IPB overvoltage protection. Replaced 12V iron battery (model L2-400). System voltage returned to normal 13.8V; fault cleared.
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.