AU
C055F00

DTC C055F00 indicates the IPB (Intelligent Integrated Brake System) detects a hydraulic circuit abnormality — Atto 3

Braking System

DTC C055F00 indicates the IPB (Intelligent Integrated Brake System) detects a hydraulic circuit abnormality.

The IPB is BYD’s electro-hydraulic integrated braking system (One-Box architecture), integrating brake boost, ESP, ABS, and EPB functions.

This fault occurs when, during a self-check or braking request, the system detects the deviation between the master cylinder pressure sensor feedback and the target pressure exceeds the limit, the hydraulic pump fails to build the required pressure within the specified time, or solenoid valve actuation feedback is abnormal.

Possible causes include hydraulic pump motor failure, pressure sensor drift, a sticking solenoid valve, brake fluid leakage/air lock, or an internal control unit sampling circuit fault.

When this fault occurs, the system may enter Limp Home mode, limiting brake boost or switching to mechanical backup mode, severely affecting braking performance.

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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1Worn carbon brushes or seized rotor in the internal DC motor (hydraulic pump) of the IPB electro-hydraulic module, preventing hydraulic pressure buildup.
  • 2Master cylinder pressure sensor (M/C Pressure Sensor) signal drift or internal open circuit; feedback pressure deviates from the actual value by more than the ±0.5 MPa threshold.
  • 3Brake line leak or critically low brake fluid causing system pressure holding test failure (leak rate > 0.1 MPa/s).
  • 4An open circuit in the solenoid valve (e.g., main valve MV, INLET valve) coil or a stuck valve spool prevents proper regulation of wheel cylinder pressure.
  • 5IPB control unit internal PCB drive circuit fault (e.g., burnt MOSFET) or abnormal ADC sampling circuit.
What To Do
  • 1
    Use the VDS2000/Launch diagnostic tool to read the complete fault codes and freeze frame data. Record key data at the time of the fault, including vehicle speed, master cylinder pressure, motor current, and solenoid valve status.
  • 2
    Visually check the brake fluid level (should be between MAX and MIN). Inspect the IPB unit, four-wheel brake lines, and hose joints for leaks or signs of fluid seepage.
  • 3
    Run the 'Hydraulic Test' function. Listen for the IPB internal hydraulic pump operating sound. Observe the pressure build-up time (normally <300 ms to reach 10 MPa). Check for timeouts or abnormal current (>15 A).
  • 4
    Check IPB supply voltage (12V±0.5V), ground resistance (<1Ω), and CAN-H/CAN-L waveforms (2.5V reference, dominant level CAN-H 3.5V/CAN-L 1.5V).
  • 5
    Disconnect the IPB low-voltage wiring harness connector and inspect the pins for oxidation or backing out; measure the master cylinder pressure sensor signal voltage (0.5V-4.5V corresponds to 0-25MPa, static voltage approximately 0.8-1.2V).
  • 6
    If the above checks are normal, perform the Bleeding Procedure to remove air from the lines and retest. If the fault persists, replace the IPB integrated electro-hydraulic module assembly.
  • 7
    After replacement, perform "System Calibration" including pressure sensor zero-point calibration, motor position learning, and solenoid valve self-test. Finally, perform a road test to verify ABS/ESP functions.
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i: Brake pedal suddenly went stiff during high-speed driving

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At 30,000 km, while driving at highway speed the dashboard suddenly displayed 'Braking System Fault'. The brake pedal became stiff with reduced travel, requiring heavy pedal effort to achieve braking force. Retrieved DTC C055F00. Freeze frame data showed master cylinder pressure at only 0.8 MPa when the fault occurred (target 12 MPa), with motor current at 18 A (over limit). Disassembled the IPB module and found the internal hydraulic pump motor carbon brushes completely worn and the commutator scored. Replaced the IPB assembly and performed the calibration procedure. Pressure build-up time returned to 200 ms. Fault resolved.
BYD DTC AI Analysis

Qin PLUS EV: Hydraulic fault after brake fluid replacement

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The vehicle stored DTC C055F00 and the ABS light stayed on after a brake fluid replacement at the workshop. Diagnosis found the technician used the conventional pedal-bleeding method, letting air into the IPB. The IPB-specific bleeding procedure (requires scan tool to cycle the motor and build pressure) failed because pressure wouldn't hold. Disassembly revealed air entering had damaged the pressure sensor diaphragm, causing signal drift. Replaced the IPB module and properly bled the system using a Pressure Bleeder to resolve the fault.
BYD DTC AI Analysis

Tang DM-p IPB Internal Short After Water Ingress

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The vehicle had waded through water deeper than the wheel hub centre. The next morning on startup it threw C055F00 and multiple communication faults. Inspection found the IPB mounted at the firewall in the engine bay with a perished housing seal allowing water ingress. Stripping the IPB revealed obvious water staining on the internal PCB; the master cylinder pressure sensor solder joints had corroded, causing the signal line to short to ground. Sensor resistance measured only 200Ω (normal 2kΩ). Replaced the IPB assembly, waterproofed the wiring harness connector, and fitted a new seal. Fault cleared. Recommend checking the brake system promptly after wading.
BYD DTC AI Analysis

Han EV: Hydraulic pump abnormal noise during winter cold start with fault code

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During cold winter morning starts in northern regions, the IPB hydraulic pump ran continuously for over 5 seconds with excessive noise, then set C055F00. Diagnosis revealed low temperatures increased brake fluid viscosity, while worn hydraulic pump bearings reduced pressure-build efficiency. The system triggered the fault code after three consecutive failed self-tests. Replaced the IPB internal hydraulic pump motor (some dealers can replace the motor assembly separately instead of the entire unit) and switched to low-viscosity DOT4 brake fluid. Cold-start testing was normal and the fault did not reoccur.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.