AU
C055F92

DTC C055F92 indicates an IPB (Integrated Power Brake) hydraulic subsystem performance fault — Qin Plus

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 Qin Plus indicates a medium-severity IPB hydraulic subsystem performance issue. The brake control unit may detect abnormal pressure, slow pressure build-up, poor pressure holding, or pump motor problems. Common causes include a worn or sticking hydraulic pump motor, low or degraded brake fluid, or moisture in the fluid. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
4
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Internal IPB 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 degraded brake fluid, or vapor lock; fluid level below the minimum mark; or moisture content exceeding 3%, causing abnormal hydraulic compressibility.
  • 3Sticking internal solenoid valve (inlet/outlet valve) or aged sealing ring in the IPB control unit causes abnormal pressure retention or internal leakage.
  • 4Wheel speed sensor signal drift or wiring interference causes the IPB to miscalculate wheel cylinder pressure demand, triggering abnormal hydraulic system regulation.
  • 5Unstable IPB power supply (poor contact at 15A fuse) or momentary CAN bus communication interruption resulting in hydraulic control command execution failure.
What To Do
  • 1
    Use VDS2000 or the BYD dedicated 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 inspect the brake fluid reservoir level. Check the IPB assembly, all four brake calipers, and brake lines for leaks. Perform a pressure holding test if necessary (pressure drop must be <10 bar 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). Inspect 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 in the sequence: right rear - left rear - right front - left front. Verify there are no air bubbles 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 ≥ 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

✓
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

✓
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

✓
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

✓
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 Qin Plus 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.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.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 Qin Plus →Qin Plus 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.