AU
C055F00

DTC C055F00 indicates the IPB (Intelligent Integrated Brake System) detects a hydraulic circuit abnormality — Atto 8

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.

The C055F00 fault code on the Atto 8 indicates an abnormal hydraulic circuit in the IPB integrated brake system. Severity is medium, but braking assistance may be reduced or the system may switch to mechanical backup mode. Common causes include hydraulic pump motor failure from worn brushes or a seized rotor, or a drifting master cylinder pressure sensor. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1Worn carbon brushes or a seized rotor in the internal DC motor (hydraulic pump) of the IPB electro-hydraulic module prevents hydraulic pressure buildup.
  • 2Master cylinder pressure sensor (M/C Pressure Sensor) signal drift or internal open circuit; feedback pressure value deviates from the actual value by more than the ±0.5MPa threshold.
  • 3Brake line leak or severely low brake fluid level causes system pressure hold test failure (leak rate > 0.1 MPa/s).
  • 4Solenoid valve (e.g., main valve MV, inlet valve INLET) coil open circuit or stuck valve spool prevents normal wheel cylinder pressure regulation.
  • 5IPB control unit internal PCB driver circuit fault (e.g., burnt MOSFET) or ADC sampling circuit malfunction.
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 (must be between MAX and MIN). Inspect the IPB unit, four-wheel brake lines, and hose joints for leaks or signs of fluid seepage.
  • 3
    Execute the 'Hydraulic Test' function, listen for the internal IPB hydraulic pump operating sound, and observe the pressure build-up time (normal: reaches 10MPa in <300ms). Check for timeout or abnormal current (>15A).
  • 4
    Check IPB supply voltage (12V±0.5V), ground resistance (<1Ω), and CAN-H/CAN-L waveform (2.5V reference, dominant level CAN-H 3.5V/CAN-L 1.5V).
  • 5
    Disconnect the IPB low-voltage wiring harness connector and check the pins for oxidation or push-out. Measure the master cylinder pressure sensor signal voltage (0.5V-4.5V corresponds to 0-25MPa, static approx. 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 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.