UK
AU
C05B000

DTC C05B000 indicates the IPB (Intelligent Integrated Braking System) detects abnormal pressure or a leak in the L2 hydraulic circuit (typically the right-rear/left-rear brake circuit, depending on vehicle brake line routing) — Seal U

Braking System

DTC C05B000 indicates the IPB (Intelligent Integrated Braking System) detects abnormal pressure or a leak in the L2 hydraulic circuit (typically the right-rear/left-rear brake circuit, depending on vehicle brake line routing).

The internal IPB hydraulic pressure sensor triggers this fault upon detecting an inability to maintain L2 circuit pressure or an abnormal pressure drop during pressure build-up.

The L2 circuit is the second hydraulic circuit in the dual-circuit braking system and controls brake pressure for specific wheels.

If the IPB detects a circuit pressure decay rate exceeding the threshold (typically >3-5 bar/s) or a failure to reach target pressure, it records the fault and enters fail-safe mode.

This mode limits or disables functions including ABS, ESC, and Automatic Emergency Braking, while retaining basic hydraulic braking capability.

This hard fault affects driving safety; clearing the DTC will not resolve the issue.

5
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Song Plus DM-i: IPB internal valve body leak causing C05B000

✓
Vehicle: 2021 Song PLUS DM-i, 32,000 km. Symptoms: ABS, ESP and Automatic Emergency Braking warning lights illuminated simultaneously. VDS read DTC C05B000 (hydraulic circuit L2 leak). Diagnosis: Brake fluid level normal. Visual inspection of L2 circuit (right rear/left rear) showed no leakage. Pressure hold test on IPB using pressure tester: L2 circuit pressure dropped from 150 bar to 80 bar in 5 seconds; L1 circuit held pressure normally. Disassembled IPB and found internal valve body seal ring aged and deformed. Solution: Replaced IPB assembly. Performed VDS online configuration (wrote IPB configuration code, calibrated sensors, ran bleed procedure). Fault cleared.
BYD DTC AI Analysis

Burst right rear brake hose caused hydraulic circuit fault

✓
Vehicle: 2022 BYD Song Pro DM-i, 48,000 km, coastal city use. Symptoms: While driving, the dash suddenly showed a brake system fault, then the ABS warning light lit up and brake pedal travel increased. Diagnosis: Scanned DTC C05B000. Found brake fluid traces on the right rear brake hose. Lifted the vehicle and found cracks near the body mounting point leaking brake fluid—salt spray corrosion had aged the rubber. Repair: Replaced the right rear brake hose (part number SA-3506800), topped up DOT4 brake fluid, performed a conventional bleed, cleared the fault codes and road tested—normal.
BYD DTC AI Analysis

Brake fluid contamination caused the IPB valve body to stick, triggering false warnings.

✓
Vehicle: 2020 Han EV, 56,000 km, non-authorised service history. Symptoms: Brake system warning light intermittent; obvious at cold start, sometimes clears after warming up. Diagnosis: Read code C05B000. Visual inspection found no external leaks. Pressure testing revealed abnormal fluctuations in the L2 circuit. Removed the IPB inlet filter and found heavy gum deposits; brake fluid was dark brown (severely degraded). Cause: substandard brake fluid and missed service intervals, causing valve sticking. Repair: Thoroughly flushed brake lines, replaced IPB assembly and brake fluid, performed full bleed and calibration. Advised customer to change brake fluid every 2 years.
BYD DTC AI Analysis

Replaced brake pads without bleeding brakes, triggering system warning

✓
Vehicle: 2021 Tang DM-i, 21,000 km. Symptoms: After replacing rear brake pads at an independent workshop, the dash displayed a brake system fault with DTC C05B000. Diagnosis: Checked brake fluid level – normal, with no leaks evident. Inquiry revealed the technician had disconnected brake hoses without performing the IPB bleed procedure, and the brake pedal felt spongy. Connected a scan tool and executed the IPB bleed procedure, operating the brake pedal as prompted. When the L2 circuit bleed valve opened, no fluid flowed, confirming air had entered the system. Resolution: Used dedicated bleeding equipment to bleed the IPB and all four calipers, performed sensor calibration, and cleared the fault.
BYD DTC AI Analysis

Damaged left rear wheel cylinder seal caused brake circuit pressure loss.

✓
Vehicle: 2019 Qin Pro EV, 68,000 km. Symptoms: Parking brake intermittently failed to release fully; dashboard showed intermittent warnings before the warning light stayed on constantly. Diagnosis: Retrieved DTCs C05B000 and C12F909 (circuit blockage — actually a secondary fault from insufficient pressure). Inspection found heavy oily sludge on the inner side of the left rear wheel, a torn wheel cylinder dust boot, and brake fluid that had leaked onto the brake disc and inside the wheel hub. Repair: Replaced the left rear brake wheel cylinder assembly, cleaned oil contamination from the brake disc surface (replaced brake pads if necessary), topped up brake fluid, performed the IPB bleed procedure, cleared the fault codes, and tested. Parking brake and service brake functions returned to normal.
Other Seal U 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.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.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
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.