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C05B001

DTC C05B001 indicates the IPB (Intelligent Integrated Brake System) detects a leak in brake hydraulic circuit L1 — Atto 3

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.

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Cases Logged
Real-World Cases
BYD DTC AI Analysis

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

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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.
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BYD DTC AI Analysis

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

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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.
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BYD DTC AI Analysis

Comprehensive Multi-circuit Leak Diagnosis and System Maintenance

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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.
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Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
Data confidence: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.