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AU
P056023

This DTC indicates the IPB (Intelligent Integrated Braking System) detected an abnormal main power supply and automatically switched to UBB (Ultracapacitor Backup Battery) power mode to maintain basic braking functions — Seal U

Braking System

This DTC indicates the IPB (Intelligent Integrated Braking System) detected an abnormal main power supply and automatically switched to UBB (Ultracapacitor Backup Battery) power mode to maintain basic braking functions.

Common causes include low voltage in the 12V low-voltage system (<9V), poor contact in the power supply circuit, abnormal DC-DC converter output, or an internal IPB power management fault.

In this mode, the system limits or disables advanced functions such as ABS, ESC, and Automatic Emergency Braking, retaining only basic hydraulic braking capability.

The brake pedal may feel harder.

This Level 2 fault affects driving safety.

5
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Qin DM no power due to invalid battery voltage signal

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Symptoms: Vehicle failed to power up; instrument cluster blacked out and auto-restarted; remote key intermittent; DTC P056023 and invalid battery voltage signal logged. Diagnosis: Measured battery static voltage at 11.2V (low), dropping to 8.5V on startup. GJK01 connector pin 14 showed poor contact with 0.3V drop, causing IPB to misread power status. Resolution: Replaced aged battery; repaired backed-out pin on GJK01 connector, re-crimped terminal and applied conductive grease; cleared fault codes with VDS. Vehicle returned to normal.
Original source ↗
BYD DTC AI Analysis

Song Pro DM-i cuts out while driving and reports voltage fault

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Symptoms: Sudden loss of power during normal driving; instrument panel displayed "Check Powertrain". Recovered after 10–30 minutes shutdown. Logged DTCs P056023 and P1A6000 (high-voltage system fault). Diagnosis: Data stream showed DC-DC output voltage fluctuating between 12.1V and 14.5V. Found oxidation at ground point G301 (DC-DC to battery negative); circuit resistance measured 2.3Ω (normal <0.1Ω). Unstable IPB power supply triggered UBB mode. Resolution: Sanded G301 ground point and applied anti-corrosion compound; replaced DC-DC-to-battery main power harness; updated VCU to latest software version.
Original source ↗
BYD DTC AI Analysis

Han EV excessive sleep current causing battery discharge and voltage fault

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Symptoms: After standing for 2–3 days, the battery discharged and the doors would not unlock. After jump-starting, the dashboard displayed ‘Battery Charging System Fault’ and DTC P056023. Diagnosis: Quiescent current (parasitic drain) measured 380 mA (specification <30 mA). Pulled fuse F4/9 (VCU supply) and current returned to normal. VCU was not entering sleep mode. Live data showed battery voltage sampling at 0 V (actual 12.4 V). Internal VCU voltage sampling circuit fault causing false readings. Resolution: Replaced Vehicle Control Unit (VCU) assembly, matched immobiliser and gateway configuration, calibrated battery voltage, and remeasured sleep current.
Original source ↗
BYD DTC AI Analysis

Tang DM Starting Difficulty and Communication Fault with P056023

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Symptoms: When cold-starting, the starter clicks but does not crank. Occasionally after starting, multiple fault lights illuminate on the instrument cluster with DTCs P056023 and B12FD (powertrain network communication fault). Diagnosis: Cranking voltage measured 7.8V, indicating severe undervoltage. Inspection revealed a burnt battery positive terminal and a loose main power screw at the engine compartment fuse box. High contact resistance caused excessive voltage drop; the low voltage triggered communication faults in the gateway module. Resolution: Replaced the battery positive cable assembly, tightened all power connections at the engine compartment distribution box, serviced the gateway module ground point G08, and retested cranking voltage.
Original source ↗
BYD DTC AI Analysis

Dolphin instrument panel battery level fault and range fluctuation

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Symptoms: Dash shows erratic battery charge and jumping range figures. Occasional "Check Low Voltage Battery System" warning while driving. DTCs P056023 and U029A (Lost Communication With Hybrid Battery Pack Sensor Module) stored. Diagnosis: VDS live data showed low voltage battery voltage reading deviated >1.5V from actual. BMS low voltage sampling connector had water ingress corrosion. Sampling resistor drift caused inaccurate voltage readings, affecting DC-DC charging strategy. Fix: Cleaned BMS low voltage sampling connector and applied circuit protectant. Replaced BMS low voltage sampling harness. Performed BMS voltage calibration and communication test.
Original source ↗
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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.