AU
P056216

P056216 is a BYD IPB (Intelligent Power Brake) extended fault code — Atto 8

Braking System

P056216 is a BYD IPB (Intelligent Power Brake) extended fault code.

It indicates the IPB control module detects its supply voltage remaining continuously below the internal threshold (typically 9V-10V; normal operating voltage is 12V±0.5V).

As the core brake-by-wire component, the IPB provides electro-hydraulic brake assist, coordinates energy recovery, and controls ESC and ABS functions.

Insufficient supply voltage reduces brake assist motor torque, causing a stiff brake pedal and extended braking distances.

This condition can also degrade or deactivate ESC and ABS functions, severely compromising driving safety.

This fault code typically triggers the IPB warning light, the ABS warning light, and a "Please check the braking system" message.

5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Low-voltage battery aging or depletion: The 12V battery in BYD hybrid/EV models (typically AGM or EFB) reaches the end of its service life or deeply discharges, causing voltage to drop below 9V during cold starts or high electrical loads.
  • 2Poor contact in the IPB power supply circuit: Backed-out terminals or loose connections at the power supply connector from the front compartment power distribution box to the IPB module (usually located near the bulkhead), or fuse holder oxidation increasing contact resistance and causing a voltage drop.
  • 3Front compartment power distribution box internal fault: Burnt relay contacts or a broken internal copper busbar inside the distribution box causes unstable output voltage at the IPB power supply terminal.
  • 4Poor earth point: A loose connection, oxidation, or residual paint at the IPB module earth point (usually G301, G302, or the left front chassis rail earth point) increases circuit resistance.
  • 5DC-DC converter fault (new energy vehicles): Abnormal output from the on-board DC-DC converter when converting high voltage to 12V low voltage, or a low-voltage charging strategy fault, causing continuously low system voltage.
What To Do
  • 1
    Fault Confirmation and Freeze Frame Analysis: Use VDS or a dedicated diagnostic tool to read the fault code. Review the freeze frame data for the specific voltage value when the fault occurred (e.g., Battery Voltage: 8.2V). Verify vehicle speed, mileage, and other conditions at the time of the fault to determine if the issue is a static battery discharge or a dynamic power supply fault.
  • 2
    Low-voltage battery condition check: Measure the battery static voltage (must be ≥12.4V). Perform an internal resistance test (CCA value must be ≥70% of the rated value). Check the battery terminals for oxidation or looseness. If the voltage is below 12V or the internal resistance is too high, replace the battery with a genuine AGM battery first.
  • 3
    IPB power supply circuit static inspection: Inspect the IPB-related fuses in the front compartment power distribution box (usually F4/9, F4/10, or 30A/40A fuses marked "IPB" or "ESC") for blown elements or oxidation. Inspect the IPB wiring harness connectors (Connector A is a large 26-pin connector, Connector B is a small 12-pin connector) for backed-out pins or signs of water ingress and corrosion.
  • 4
    Dynamic voltage measurement: Turn the key to the ON position (do not press the brake pedal). Use a multimeter to measure the voltage to ground at IPB connector pin 1 (Terminal 30 constant power) and pin 14 (Terminal 15 ignition power); the voltage must be ≥11.5V. Measure the voltage drop between the IPB ground point (usually connected to the left front frame rail) and the battery negative terminal; the voltage drop must be <0.1V. An excessive voltage drop indicates high circuit resistance.
  • 5
    Power distribution box output test: If the power distribution box input voltage is normal (battery voltage) but the output voltage to the IPB is low, disassemble the power distribution box and inspect the internal relay contacts for burning. Replace the front compartment power distribution box assembly if necessary.
  • 6
    Clean and tighten ground points: Remove IPB ground points (G301/G302). Sand the contact surfaces to bare metal. Apply conductive grease, then tighten to the standard torque (usually 8-10 N·m). Check the body ground stud for stripped threads.
  • 7
    DC-DC function verification (new energy vehicles): With the vehicle in READY mode, measure the charging voltage across the battery terminals. The voltage must be 13.8V-14.5V. If the voltage remains below 13V, check the DC-DC low-voltage output circuit. Update the DC-DC control software or replace the DC-DC assembly if necessary.
  • 8
    Fault repair and function verification: After repairing or replacing the faulty component, clear the fault codes and perform the IPB system bleeding procedure (use the diagnostic tool to execute the "Electro-hydraulic Brake System Bleeding" process). Road test the vehicle to confirm normal brake pedal effort and no illuminated warning lights. Read the fault codes again to verify P056216 does not return.
Real-World Cases
BYD DTC AI Analysis

Song Plus DM-i IPB power supply connector pin backed out causing intermittent brake fault

✓
While driving, the instrument cluster intermittently displayed "Brake System Fault". Both the IPB and ABS warning lights came on together and the brake pedal went hard. Scanned with a diagnostic tool and retrieved codes P056216 (System Voltage Low) and C123456 (IPB Power Supply Abnormal). Freeze frame data showed 8.1V at the time of the fault. Measured voltage at IPB connector pin A-1 (constant power) and found it swinging between 8V-12V while wiggling the wiring harness. Disassembled the IPB connector and found pin 1 (thick red wire) had backed out—the internal latch had broken, allowing the pin to retract. Fix: Used a special pin removal tool to re-crimp the pin. Replaced the IPB wiring harness connector (Part No.: GJ-XXX-XXXX) and seated the pin fully. Voltage stabilized and the fault cleared.
Original source ↗
BYD DTC AI Analysis

Burnt relay contacts inside the front compartment power distribution box caused IPB undervoltage

✓
After parking overnight, the owner reported a brake system fault and DTC P056216 on morning startup; the warning light cleared after driving. The low voltage battery voltage was normal but dropped to 9.8V during startup. Voltage at the IPB fuse output measured only 10.2V with the key ON, while the distribution box input (B+) showed 12.4V—a 2.2V drop. Inspection of the front compartment distribution box revealed severely burnt and blackened contacts on the IPB power relay, with contact resistance of 0.8Ω. Replaced the front compartment distribution box assembly (part number: SA-XXX-XXXX) and checked the IPB module for internal shorts causing excessive current. Post-replacement voltage at the IPB measured 12.3V; fault resolved.
Original source ↗
BYD DTC AI Analysis

Degraded low-voltage AGM battery triggers P056216 during cold start

✓
2021 Song PLUS DM-i. Two years in, the dash threw "Check Brake System" on cold starts. Scanned P056216. Fault appeared whenever ambient temp dropped below 10°C and cleared once warm. Static battery voltage measured 12.1V (low). CCA down to 45% of rated, SOH 60%. Cranking crashed voltage to 8.5V—below IPB threshold. Root cause: owner only took short trips with Battery Intelligent Charging off, so the battery sulfated from chronic undercharge. Fix: Replaced with genuine 60Ah AGM (E6A-XXX-XXXX), turned on Battery Intelligent Charging via the scan tool, and advised the owner to fully charge every two weeks. Cold start voltage now holds above 11.2V. Fault hasn't returned.
Original source ↗
BYD DTC AI Analysis

Oxidized body ground point caused intermittent IPB undervoltage

✓
When driving on rough roads, the instrument cluster intermittently flashed the brake warning light. The scanner showed P056216 as an intermittent fault. IPB supply voltage was normal, but checking the ground circuit revealed a 0.3V drop between the IPB housing and battery negative terminal, with unstable resistance. Found the G302 ground point on the left front longitudinal member had a loose ground wire bolt, plus white oxide and paint residue on the contact surface. Repair: Removed the ground wire, sanded the contact surface to bare metal with 80-grit sandpaper, applied conductive paste (not grease), and torqued the bolt to 9N·m. Also inspected the IPB housing ground wire (black heavy-gauge cable) ring terminal for cracks. After repair, ground voltage drop measured under 0.05V. Road-tested 50 km with no fault recurrence.
Original source ↗
BYD DTC AI Analysis

Unstable DC-DC converter output caused low system voltage while driving

✓
Driving in EV mode with headlights and A/C on, the instrument cluster showed a brake system fault. DTCs P056216 and U01A987 (IPB communication fault) appeared simultaneously. Battery voltage dropped instantly from 13.8V to 9.5V when high-power loads came on, fluctuating constantly. At the DC-DC low-voltage output terminals, voltage was unstable, oscillating between 12V and 14V. The scan tool showed a history of 'low-side overcurrent protection' in the DC-DC data stream. Inspection found an internal loose connection in the positive harness from the DC-DC converter to the battery (runs through the front compartment fuse box). Fix: Replaced the harness from the DC-DC to the fuse box (including fuse) and flashed the DC-DC control software to V2.3.5 or above. Post-repair load testing confirmed voltage stable at 13.5V±0.2V. Fault resolved.
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.