AU
C055F92

DTC C055F92 indicates an IPB (Integrated Power Brake) hydraulic subsystem performance fault — Atto 8

Braking System

DTC C055F92 indicates an IPB (Integrated Power Brake) hydraulic subsystem performance fault.

This DTC indicates the IPB control unit detects abnormal hydraulic circuit pressure, excessive pressure build-up time, insufficient pressure holding capability, or abnormal hydraulic pump motor operation.

The IPB system integrates electric vacuum assist, ESP electronic stability control, and ABS anti-lock braking functions.

This fault may reduce brake assist, harden the brake pedal, restrict or disable active safety functions (AEB/ACC), or in extreme cases, trigger the brake system downgrade protection mode.

The fault suffix '92' indicates a hydraulic circuit performance deviation or intermittent operating abnormality rather than a complete failure.

4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1IPB internal hydraulic pump motor wear or seizure causing insufficient pressure build-up or delayed response, common in high-mileage vehicles or due to internal corrosion caused by overdue brake fluid replacement.
  • 2Insufficient, degraded, or air-locked brake fluid; fluid level below the minimum mark or water content exceeding 3% causes abnormal hydraulic compressibility.
  • 3Sticking IPB control unit internal solenoid valve (inlet/outlet valve) or aged sealing ring causes abnormal pressure retention or internal leakage.
  • 4Wheel speed sensor signal drift or wiring interference causes the IPB to incorrectly determine wheel cylinder pressure demand, resulting in abnormal hydraulic system regulation.
  • 5Unstable IPB power supply (poor 15A fuse contact) or momentary CAN bus communication interruption, causing hydraulic control command execution failure.
What To Do
  • 1
    Use VDS2000 or a dedicated BYD diagnostic tool to read the complete fault codes and freeze frame data. Record key parameters at the time of the fault, including vehicle speed, master cylinder pressure, and motor current. Check for accompanying wheel speed-related faults such as C003F and C0040.
  • 2
    Visually check the brake fluid reservoir level. Inspect the IPB assembly, four-wheel brake calipers, and brake lines for leaks. Perform a pressure holding test if necessary (pressure drop must be <10 bar over 10 minutes).
  • 3
    Measure the IPB assembly power supply voltage (12.5-14.5V), ground resistance (<1Ω), and CAN-H/CAN-L waveform (2.5V reference, dominant level 3.5V/1.5V). Check the 30-pin IPB connector terminals for backed-out pins or oxidation.
  • 4
    Perform the IPB system bleeding procedure: Use the diagnostic tool to activate bleeding mode, bleed the system in the order of right rear - left rear - right front - left front, and verify no air bubbles are present and brake pedal travel is normal.
  • 5
    Check brake fluid quality using a brake fluid moisture tester. If moisture content is >3% or the fluid is cloudy, completely replace the DOT4 brake fluid and flush the system.
  • 6
    If the above checks are normal, update the IPB software (version must be ≥2023-Q2). After the update, clear the fault codes and perform a 30-minute road test, including an emergency braking test at speeds above 40 km/h.
  • 7
    If the fault recurs, replace the IPB integrated electro-hydraulic module assembly. After replacement, use the diagnostic tool to perform coding, longitudinal acceleration sensor calibration, and ESP function learning.
Real-World Cases
BYD DTC AI Analysis

Aging IPB pump motor in Song PLUS DMi caused intermittent pressure build-up failure

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82,000 km. Owner reported the instrument cluster intermittently displaying "Braking System Fault," with the brake pedal going hard when the warning light illuminated. The scan tool retrieved C055F92 and C055E00 (hydraulic pump motor fault). Freeze frame data showed 120 bar master cylinder pressure demand against 68 bar actual, with motor current spiking to 18 A (normal <12 A). Disassembled the IPB and found the motor carbon brushes worn beyond limits and the commutator scored. Replaced the IPB assembly and reflashed the software. Fault resolved.
BYD DTC AI Analysis

Brake fluid leak caused insufficient hydraulic system pressure

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2021 Song PLUS DM-i. ESC and ABS warning lights lit up simultaneously while driving. Inspection found slight seepage at the left rear wheel cylinder and brake fluid below MIN. Low fluid prevented the IPB accumulator from building adequate pressure, triggering C055F92. Replaced the left rear wheel cylinder repair kit and brake fluid, bled the system, and cleared the fault code. Advised the owner to replace brake fluid every 2 years to prevent recurrence.
BYD DTC AI Analysis

Wheel speed sensor signal interference caused hydraulic system false alarm

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Vehicle frequently set DTC C055F92 when driving on rough roads; operated normally on smooth surfaces. Inspection revealed the right front wheel speed sensor harness was rubbing against the steering knuckle, with worn insulation causing an intermittent short. When the IPB detected sudden wheel speed signal fluctuations, it misinterpreted these as wheel lock-up and repeatedly adjusted hydraulic pressure, eventually triggering a hydraulic system performance fault. Repaired the harness and secured its routing; the fault has not returned.
BYD DTC AI Analysis

IPB software calibration error causing cold-start fault

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In -10°C winter temperatures, DTC C055F92 appeared every cold start and cleared after 10 minutes driving. Diagnosis revealed outdated IPB software with a defective pressure sensor zero-drift compensation algorithm for low temperatures. Upgraded IPB software to IPB_3.2.1_CN via VDS2000 and performed sensor zero-point calibration. 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.