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C055F92

DTC C055F92 indicates an IPB (Integrated Power Brake) hydraulic subsystem performance fault — Seal 6 EV

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.

The C055F92 fault code on the Seal 6 EV indicates a medium-severity problem with the IPB hydraulic brake system, where pressure may build too slowly, not hold correctly, or the pump motor may operate abnormally. Common causes include a worn or sticking hydraulic pump motor, low or degraded brake fluid, or air in the brake system. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 1IPB internal hydraulic pump motor wear or seizure causing insufficient pressure build-up or delayed response, common in high-mileage vehicles or resulting from internal corrosion due to overdue brake fluid replacement.
  • 2Insufficient or deteriorated brake fluid, or air lock; fluid level below the minimum mark or water content exceeding 3%, causing abnormal hydraulic compressibility.
  • 3IPB control unit internal solenoid valve (inlet/outlet valve) sticking or aged sealing ring, causing abnormal pressure retention or internal leakage.
  • 4Wheel speed sensor signal drift or circuit interference causes the IPB to miscalculate wheel cylinder pressure demand, resulting in abnormal hydraulic system regulation.
  • 5Unstable IPB power supply (poor contact at the 15A fuse) or momentary CAN bus communication interruption, causing failure to execute the hydraulic control command.
What To Do
  • 1
    Use VDS2000 or the dedicated BYD diagnostic tool to read the complete fault codes and freeze frame data. Record key parameters at the time of the fault, such as 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. Check the IPB assembly, all four brake calipers, and brake lines for leaks. If necessary, perform a pressure holding test (pressure drop must be <10bar during a 10-minute hold).
  • 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 following order: right rear - left rear - right front - left front. Verify no air bubbles are present and pedal travel is normal.
  • 5
    Check brake fluid quality. Measure moisture content 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 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 matching, 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 Seal 6 EV Fault Codes
B1108For 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.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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV 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.