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C05B001

DTC C05B001 indicates the IPB (Intelligent Integrated Brake System) detects a leak in brake hydraulic circuit L1 — Qin Plus

Braking System

DTC C05B001 indicates the IPB (Intelligent Integrated Brake System) detects a leak in brake hydraulic circuit L1.

The IPB is the BYD brake-by-wire system (One-Box architecture) integrating brake assist, Electronic Stability Control (ESC), and energy recovery functions.

Circuit L1 typically refers to the primary brake circuit or a specific wheel cylinder control circuit (e.g., front left wheel circuit).

This fault indicates hydraulic system sealing failure.

This condition can extend brake pedal travel, cause a non-linear reduction in braking force output, and restrict or disable active safety functions including ABS, ESC, and Automatic Emergency Braking.

Due to braking safety risks, the system illuminates multiple warning lights and may limit vehicle power output.

3
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Brake caliper (wheel cylinder) piston seal aged, damaged, or improperly installed, causing hydraulic fluid leakage.
  • 2Visible leakage caused by loose, corroded, or physically damaged steel brake pipes or rubber hose fittings.
  • 3Worn master cylinder sealing ring or failed valve body seal inside the IPB integrated brake module (internal leakage)
  • 4Prolonged failure to replace brake fluid causes excessive water content, leading to seal swelling, corrosion, or rusting of metal components.
  • 5Excessive brake pad wear causes brake caliper piston overtravel, displacing the seal ring and causing leakage.
What To Do
  • 1
    Park the vehicle safely, disconnect the high-voltage power supply, and check if the brake fluid reservoir level has dropped abnormally.
  • 2
    Use the VDS2000/3000 diagnostic tool to read the fault code and freeze frame data to confirm the specific operating conditions of the L1 circuit pressure build-up failure.
  • 3
    Visually inspect the hoses, steel pipes, fittings, and brake wheel cylinders of the corresponding L1 circuit lines (usually involving the front left wheel or main circuit) for signs of fluid leakage.
  • 4
    Perform the brake system pressure holding test. Use the diagnostic tool to drive the IPB motor to build hydraulic pressure. Monitor the pressure drop rate to determine if it exceeds the limit and locate the leak point.
  • 5
    Disassemble and inspect the brake caliper piston seal condition, check the caliper sliding pins for binding, and inspect the brake pad wear.
  • 6
    Replace the failed component based on the inspection results: if an external line or wheel cylinder leaks, replace the corresponding component; if the IPB leaks internally, replace the IPB electro-hydraulic module assembly with ECU.
  • 7
    Thoroughly bleed the brake system according to the standard BYD procedure. Ensure no air remains in the L1 circuit and related circuits.
  • 8
    Fill with DOT 4 or the specified brake fluid to the MAX level, then perform the IPB system self-learning and pressure calibration procedure.
  • 9
    Clear the fault code, perform a static function test (pedal feel check) and a dynamic road test (ABS activation test), and confirm the fault is resolved.
Real-World Cases
BYD DTC AI Analysis

BYD Seal 06 DM-i Brake Hydraulic Circuit L1 Leak Repair

✓
The dashboard showed a constant brake system warning light and brake pedal travel increased noticeably. The scan tool retrieved DTC C05B001 (brake hydraulic circuit L1 leak), along with abnormally low brake fluid level. During diagnosis, the technician confirmed the DTC and freeze frame data. Visual inspection revealed brake fluid leak traces at the left front brake caliper. Disassembly revealed the caliper piston seal cracked from aging. The technician replaced the left front brake caliper assembly and damaged seal, thoroughly bled the brake system, and topped up the brake fluid to the standard level. After the repair, the technician cleared the DTC. A road test confirmed the hydraulic circuit sealed normally and ABS functioned properly.
Original source ↗
BYD DTC AI Analysis

Atto 3 (Yuan Plus) brake hydraulic circuit L1 leak diagnosis

✓
The instrument cluster displayed a brake system fault. The scanner showed C05B001 (Brake Hydraulic Circuit L1 Leaky) with occasional abnormal ESP intervention. During diagnosis, a full code scan revealed C2A1700 (Brake Hydraulic Circuit L1 Overcompensated/Air Present). The brake booster motor and pressure sensor checked normal. Pressure-testing brake hydraulic circuit L1 showed the pressure wouldn’t hold. Further inspection found leakage at the right rear wheel cylinder hydraulic line connection and a worn piston seal. Tightened and replaced the leaking hydraulic line fitting, replaced the right rear brake wheel cylinder assembly, and bled the brake system to clear all air.
Original source ↗
BYD DTC AI Analysis

Comprehensive Multi-circuit Leak Diagnosis and System Maintenance

✓
The vehicle had simultaneous DTCs C05B001 (L1 circuit leak) and C05B000 (L2 circuit leak), a spongy brake pedal, uneven brake force distribution, and multiple brake warning lights illuminated on the dashboard. During diagnosis, the technician thoroughly inspected the brake hydraulic circuits and found physical damage and corrosion on several lines, plus contaminated fluid in the brake fluid reservoir. The technician ran a brake system self-test with the diagnostic tool and observed slow pressure build-up and an inability to hold pressure. Inspection revealed severely contaminated brake fluid (moisture content exceeded specifications), causing multiple seals to swell and leak. The repair involved replacing all aged brake hoses and seals, thoroughly flushing and replacing the brake fluid throughout the vehicle, and replacing the brake fluid reservoir filter. The ABS pump also showed minor internal leak signs, so the technician recommended replacing the ABS/ESP assembly. The system returned to normal after the repair.
Original source ↗
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.