AU
C000300

DTC C000300 indicates an electrical fault in Traction Control System (TCS) control valve B inside the Intelligent Integrated Braking System (IPB) (fault type 1 typically indicates an open circuit, short circuit, or out-of-range performance) — Qin Plus

Braking System

DTC C000300 indicates an electrical fault in Traction Control System (TCS) control valve B inside the Intelligent Integrated Braking System (IPB) (fault type 1 typically indicates an open circuit, short circuit, or out-of-range performance).

In the BYD One-Box braking system, the TCS solenoid valve regulates brake fluid pressure when the drive wheels slip, restoring traction by applying intermittent braking to the slipping wheels.

This fault means the IPB module detects an abnormal drive circuit for valve B or a valve body response exceeding the calibrated threshold, disabling the TCS function.

Normal braking remains unaffected.

However, when starting or accelerating on low-traction surfaces such as ice, snow, or mud, the drive wheels may spin uncontrollably, compromising driving safety.

This is an internal actuator fault within the IPB hydraulic control unit.

Use professional diagnostic equipment to determine whether the fault lies in the solenoid valve itself or the control circuit.

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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1Open circuit, short circuit, or short to ground in the TCS solenoid valve B coil inside the IPB electro-hydraulic module, causing abnormal drive current.
  • 2Brake fluid overdue for replacement or contaminated with impurities causes the solenoid valve spool to stick in the open/closed position, resulting in a response timeout.
  • 3Water ingress, oxidation, or terminal back-out at the IPB module wiring harness connector (especially the 32-pin main connector), causing abnormal power supply or signal transmission.
  • 4A damaged internal power driver chip (MOSFET) in the IPB control unit prevents solenoid valve actuation.
  • 5Previous chassis bottoming out or collision caused mechanical damage to the internal valve body of the IPB assembly.
What To Do
  • 1
    Use VDS or a BYD dedicated diagnostic tool to read the complete fault codes and freeze frame data. Confirm whether C000300 is a current or historical fault. Record the vehicle speed, wheel speed, and other data at the time the fault occurred.
  • 2
    Visually inspect the IPB electro-hydraulic module exterior for brake fluid leaks, housing damage, or loose wiring harness connectors. Focus on the sealing condition around the TCS valve body.
  • 3
    Disconnect the IPB main power supply and measure the resistance of TCS solenoid valve B (standard value: 2.5-5.0 Ω; refer to the repair manual for exact specifications). If the resistance is infinite or close to 0 Ω, this confirms a coil fault.
  • 4
    Check the IPB supply voltage (BAT+ to GND should be 11-14V) and ground point tightness. Measure the insulation resistance to ground of the solenoid valve drive wiring harness to rule out short or open circuits.
  • 5
    Check brake fluid condition. If water content is > 3% or contains visible impurities, replace all brake fluid and flush hydraulic lines to eliminate valve body sticking.
  • 6
    After clearing the fault code, run the IPB self-check procedure (conditions: ignition switch ON, brake pedal released, wheel speed 0) and observe if the self-check passes. If the fault recurs, replace the IPB electro-hydraulic module assembly.
  • 7
    After replacing the IPB, use the diagnostic tool to perform the "Brake System Bleeding" procedure (activating the motor pump to bleed each wheel cylinder in sequence), and complete the "Pressure Sensor Calibration" and "Longitudinal Acceleration Sensor Calibration".
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i IPB internal TCS valve coil open circuit fault

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Vehicle: 2021 Song Plus DM-i 110KM, 32,000 km. Symptoms: ABS, ESP, and TCS OFF warning lights illuminated simultaneously on the instrument cluster. VDS retrieved DTC C000300 (TCS Control Valve B Fault 1). Diagnosis: Measured resistance at the TCS Valve B drive pin on the IPB 32-pin connector. Reading was infinite (spec: 3.2Ω), indicating an open circuit in the valve body coil. Disassembled the IPB assembly and found the solenoid valve B pin solder joint fractured from vibration. Repair: Replaced the IPB electro-hydraulic brake module assembly (P/N SC-3635010). Performed brake system bleed procedure and sensor calibration. Fault resolved.
BYD DTC AI Analysis

Brake fluid contamination caused TCS valve sticking

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Vehicle: Song Plus DM-i, 58,000 km, brake fluid overdue per maintenance schedule. Symptoms: ESC warning light illuminated intermittently after driving in wet conditions. Scan tool read C000300, but the fault cleared after cycling the ignition. Diagnosis: Brake fluid tested dark brown with 4% moisture. Removed and inspected IPB inlet strainer; found metal debris. Suspect degraded brake fluid caused TCS solenoid B valve to stick, triggering a response timeout. Repair: Flushed brake lines thoroughly, replaced fluid with DOT4 low-viscosity grade (2 L), and performed IPB activation test. No recurrence after cleaning. Advised customer to replace brake fluid every two years.
BYD DTC AI Analysis

Water ingress into the IPB wiring harness connector caused abnormal power supply to the TCS valve.

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Vehicle: Song Pro DM. Braking system fault after wading. Symptoms: Dashboard displayed "Braking System Fault." DTCs C000300 and C000200 present (TCS control valve A fault). Repair procedure: IPB module located on left side of engine bay. Found 32-pin main connector seal deteriorated with obvious water ingress and verdigris inside. Measured TCS valve B supply voltage fluctuating between 7–9 V (normal 12 V); connector oxidation caused excessive contact resistance. Resolution: Cleaned connector pins, applied conductive paste, replaced waterproof seal. Restored power; voltage stabilized. Cleared fault codes; system returned to normal.
BYD DTC AI Analysis

IPB control unit drive circuit fault false positive

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Vehicle: Qin PLUS EV, 2000 km (new vehicle). Symptoms: No warning lights, but scan tool showed historic fault code C000300. Repair: Checked TCS solenoid B resistance (2.8 Ω – normal); wiring harness continuity normal. Inspected IPB control unit internal drive circuit: found intermittent conduction failure in solenoid B low-side drive MOSFET, causing valve actuation to deviate from drive signal. Solution: Replaced IPB electro-hydraulic module (IPB is an assembly component). Performed 'After-sales EOL configuration' via scan tool to write vehicle VIN and configuration parameters. Completed brake bleed calibration; fault resolved.
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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.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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.