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 — Atto 8

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
5
Causes
Likely Causes — Atto 8
  • 112V low-voltage battery aging, depletion, or capacity degradation causes the voltage to fall outside the IPB operating threshold (usually <9V or >16V).
  • 2Poor contact in the IPB power supply circuit, including backed-out pins, oxidation, or burn damage at the connectors between the front compartment distribution box and the IPB (GJK01, etc.), or loose ground points (G301/G08).
  • 3Abnormal or fluctuating DC-DC converter output voltage (hybrid/battery electric vehicles), causing unstable low-voltage system power supply and failing to meet IPB main power requirements.
  • 4Fault in the IPB internal power management module or voltage sampling circuit, causing a false power mode switch report.
  • 5Vehicle charging system fault (generator/DC-DC) causes continuous battery voltage drop during driving and triggers backup power supply protection.
What To Do
  • 1
    Use the BYD VDS diagnostic tool to read the complete fault codes and freeze frame data. Check the actual supply voltage (Battery_Voltage), backup power supply status, and historical fault records in the IPB data stream.
  • 2
    Check the 12V low-voltage battery status: measure the static voltage (should be ≥12.4V) and the cranking/driving dynamic voltage (should not be <9V). If necessary, perform a battery State of Health (SOH) inspection and a charging test.
  • 3
    Check the IPB power supply circuit: Check the IPB fuse in the front compartment fuse box (usually F4/9 or F1/16). Measure the voltage and voltage drop at the power supply pins of connectors such as GJK01/G2K01 (voltage drop should be <0.3V). Inspect the pins for push-out, burning, or water ingress.
  • 4
    Check ground points: Tighten and clean key ground points such as G301 (left front compartment) and G08 (left dashboard), and measure circuit resistance (should be <0.1Ω).
  • 5
    For hybrid/EV models, check the DC-DC converter output voltage stability (must remain stable at 13.5-14.5V). Eliminate low-voltage charging system faults and update the VCU/BMS software if necessary.
  • 6
    If the external power supply and wiring are normal but the IPB still reports a fault, replace the IPB electro-hydraulic module assembly, bleed the brake system, calibrate the pedal position, and perform an ESC function test.
Real-World Cases
BYD DTC AI Analysis

Qin DM no power due to invalid battery voltage signal

✓
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

✓
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 Atto 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.