AU
C104400

DTC C104400 indicates the IPB (Integrated Power Brake) system detects an incomplete or insufficient hydraulic brake line bleeding procedure — Seal 6 EV

Braking System

DTC C104400 indicates the IPB (Integrated Power Brake) system detects an incomplete or insufficient hydraulic brake line bleeding procedure.

The IPB system uses internal pressure sensors to monitor the hydraulic pressure build-up characteristics of each brake wheel cylinder.

When the system detects air in the lines (abnormal compressibility) or identifies an incorrectly executed bleeding procedure, it triggers this fault code and enters fail-safe mode.

This fault restricts ABS/ESP functions, causes abnormal brake pedal travel (spongy pedal), and derates or disables the Automatic Emergency Braking (AEB) function, severely impacting braking safety and driver assistance system performance.

The C104400 fault code on the Seal 6 EV indicates the IPB brake system has detected an incomplete or insufficient hydraulic brake bleeding procedure. This is a medium-severity fault that can cause a spongy pedal and limit ABS, ESP, or AEB functions. Common causes include skipped brake bleeding after service or low battery voltage during the IPB bleeding process. Visit an authorised dealer for proper bleeding and calibration. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 1Failure to perform the standard bleeding procedure after servicing the brake system (replacing brake fluid, brake hoses, brake calipers, or brake pads), or manual interruption of the bleeding process.
  • 2During the IPB electro-hydraulic module internal bleeding procedure, battery voltage dropped below 12 V or diagnostic communication failed, causing a calibration data write failure.
  • 3Bleeding the system with non-dedicated equipment (such as traditional pedal pumping) fails to trigger the IPB active pressure-building bleed mode, preventing the system from recognizing the bleeding completion status.
  • 4Severely low brake fluid or a leaking hydraulic line prevents the bleeding procedure from building sufficient system pressure to complete the self-check.
  • 5Outdated IPB control unit software version, or abnormal internally stored bleed status flag (false positive fault).
What To Do
  • 1
    Pre-inspection check: Confirm brake fluid level is within the MAX-MIN range, check all four wheel brake lines for leaks, verify battery voltage is ≥12.5V, and ensure normal diagnostic tool communication.
  • 2
    Enter bleed mode: Use the BYD VDS or Bosch dedicated diagnostic tool to access the IPB system → Special Functions → Hydraulic Brake Bleeding/Refill Procedure. Strictly follow the prompted sequence (usually right rear, left rear, right front, left front).
  • 3
    Perform active bleeding: Connect the diagnostic tool and follow the on-screen prompts to bleed each wheel in sequence. The IPB motor actively builds high pressure (approximately 20-30 bar). Open the corresponding wheel cylinder bleed screw within the specified time until bubble-free fluid flows out.
  • 4
    Complete calibration: After bleeding all four wheels, use the diagnostic tool to perform 'Bleeding Completion Confirmation' and 'System Pressure Calibration'. Verify successful zero-point calibration of the IPB internal pressure sensor. Read the data stream to confirm the pressure build-up time difference across all four wheels is <50ms.
  • 5
    Function verification: Clear the fault code, perform a road test (vehicle speed > 40 km/h), verify normal ABS activation, check that the instrument cluster ABS/ESC warning light is off, and confirm the Automatic Emergency Braking (AEB) function operates normally.
Real-World Cases
BYD DTC AI Analysis

Electronic bleed procedure not performed after brake fluid replacement on Song PLUS DM-i

✓
After bringing the vehicle in for maintenance and brake fluid replacement, the instrument cluster displayed 'Brake System Fault' with DTC C104400. The technician only performed conventional manual pedal bleeding without executing the IPB active bleeding procedure via VDS. They then used the diagnostic tool to access the IPB system and executed the 'Hydraulic Brake Bleeding' special function, completing active bleeding in the right-rear, left-rear, right-front, left-front sequence. The DTC cleared automatically and brake pedal firmness returned to normal.
BYD DTC AI Analysis

Battery discharged during repair, interrupting the exhaust process

✓
Replaced the left rear wheel cylinder due to a brake fluid leak. Did not connect a stabilized power supply during the repair. During brake bleeding, battery voltage dropped to 10.8V, causing the IPB control unit to restart and set C104400, which could not be cleared. Inspection found the IPB internal bleed counter abnormal. Connected a stabilized power supply to maintain voltage above 13V, performed the complete four-wheel brake bleeding procedure again, and executed 'control unit reset' and 'longitudinal and lateral sensor calibration' after bleeding was complete. Fault resolved.
BYD DTC AI Analysis

False exhaust fault due to IPB software false alarm

✓
No prior service history. ABS warning light intermittent. Read fault code C104400; brake pedal felt normal. No brake fluid leaks. Attempted bleed procedure; display indicated "completed" but fault code persisted. Diagnosis found IPB software was early version with a bug. Solution: Upgraded IPB control unit software to latest version (via BYD OTA or offline programming). Fault code cleared after upgrade. No recurrence after one week of monitoring.
Other Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.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 Seal 6 EV →Seal 6 EV 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.