AU
C05D200

This fault code indicates an internal pressure sensor monitoring fault within the IPB (Integrated Power Brake) — Seal U

Braking System

This fault code indicates an internal pressure sensor monitoring fault within the IPB (Integrated Power Brake).

Specifically, during self-test or operation, the IPB control unit detects the voltage signal from the brake master cylinder pressure sensor (or wheel cylinder pressure sensor, depending on configuration) falls below the calibrated normal operating threshold (typically corresponding to an equivalent voltage for a pressure below 0.1-0.3MPa).

Potential causes include sensor drift, an open circuit causing signal loss (reading 0V or extremely low voltage), or an internal IPB hydraulic circuit leak preventing actual pressure buildup.

This fault triggers the brake system degradation mode and may disable the ABS, ESC, Automatic Emergency Braking (AEB), and energy recovery functions.

Extreme conditions may limit vehicle speed and illuminate multiple warning lights.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1A damaged or aged master cylinder pressure sensor inside the IPB electro-hydraulic module causes an abnormally low output signal voltage.
  • 2Open circuit or short circuit (short to ground) in the pressure sensor 5V reference power supply circuit or signal feedback circuit, causing the ECU to detect abnormally low voltage.
  • 3IPB internal brake master cylinder seal leak or valve body leak causes actual pressure to fall below the sensor threshold during pressure build-up.
  • 4Loose IPB control unit connector, corrosion from water ingress, or backed-out pins interrupting sensor signal transmission.
  • 5Severe brake fluid loss or air in the system prevents pressure build-up, causing the sensor to report an actual low-pressure condition.
What To Do
  • 1
    Safety preparation: Confirm the vehicle is stationary and apply the electronic parking brake. Use a BYD VDS or Launch/Autel diagnostic tool to read the complete fault codes and freeze frame data. Record the vehicle speed, pedal travel, and pressure values at the time of the fault.
  • 2
    Basic inspection: Check if the brake fluid reservoir level is between MAX and MIN, inspect the exterior of the IPB electro-hydraulic module for leaks or impact damage, and check the related chassis wiring harness for damage.
  • 3
    Data stream analysis: Access the IPB system to read the data stream. Observe 'master cylinder pressure sensor voltage' and 'master cylinder pressure value'. With the pedal released, the voltage should read 0.4-0.6V (corresponding to 0MPa). A reading of 0V or below 0.1V indicates a wiring or sensor fault.
  • 4
    Circuit measurement: Disconnect the IPB connector. Measure the voltage between the pressure sensor reference voltage terminal and ground; it should be 5 V ± 0.25 V. Measure the signal wire resistance; it should be less than 1 Ω. Measure the resistance between the signal wire and ground; it should be greater than 10 MΩ. Check the pins for oxidation or enlarged holes.
  • 5
    Pressure test: Press the brake pedal and verify the data stream pressure value rises linearly with pedal travel. If the pressure does not rise but the sensor voltage is normal, this indicates an internal mechanical leak in the IPB.
  • 6
    Component replacement: If testing confirms a sensor fault and the IPB is an integrated non-serviceable unit, replace the IPB electro-hydraulic module assembly. If the wiring harness is faulty, repair the harness.
  • 7
    System calibration: After replacement or repair, perform the 'Brake System Bleeding' procedure (use the diagnostic tool to actuate the fluid pump), perform the 'Pressure Sensor Zero-Point Calibration', perform the 'ESC Function Test', clear the fault codes, and road test to verify.
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i IPB internal leak caused pressure sensor to read low

✓
The vehicle came in with the ABS and ESP warning lights on and a soft brake pedal. Retrieved DTC C05D200. Live data showed the master cylinder pressure sensor at 0.3V (abnormally low); maximum pressure reached only 1.2MPa with the pedal applied (normal: 8-12MPa). Disassembled the IPB electro-hydraulic module and found the internal master cylinder seals degraded and leaking. This prevented pressure build-up and the sensor correctly indicated low pressure. Replaced the IPB assembly, bled the brakes, performed pressure calibration, and cleared the fault.
BYD DTC AI Analysis

Intermittent contact fault in Seal EV sensor connector

✓
Owner reported the brake system warning light came on intermittently during cold starts and cleared after the vehicle warmed up. Scan tool read historical DTC C05D200; live data showed normal readings. Inspection found the pressure sensor connector on the IPB module loose with oxidized pins. Cold-state metal contraction increased contact resistance, pulling the signal voltage low. Tightened the connector pins using a special tool, applied conductive paste, and re-secured the plug. One week of monitoring showed no recurrence.
BYD DTC AI Analysis

Han EV fault after brake fluid replacement without calibration

✓
Vehicle set DTC C05D200 the day after a brake fluid change at the dealership. Brake pedal feel was normal but the warning light stayed on. Inspection revealed the technician used traditional manual bleeding rather than the electronic bleed procedure with a diagnostic tool, trapping air inside the IPB; the pressure sensor detected abnormally low pressure. Used VDS to perform 'Brake System Bleed' (pump actively pressurises to bleed) and 'Pressure Sensor Zero Point Calibration'. Cleared the fault code and it has not returned.
BYD DTC AI Analysis

Tang DM-i wiring harness short after accident repair

✓
Vehicle involved in a front-end collision. After repairs, the dashboard displayed "Brake System Fault". Read DTC C05D200. Found the IPB module wiring harness crushed in the accident, with the pressure sensor signal wire insulation damaged and shorted to ground, causing the ECU to read 0V. Repaired the damaged wiring. Measured sensor reference voltage at 5V (normal). Signal voltage varied normally with brake pressure (0.5V–4.5V). Cleared fault codes and road tested — all functions normal.
BYD DTC AI Analysis

Outdated Qin PLUS DM-i software version causing false fault codes

✓
No abnormal braking feel, but DTC C05D200 set intermittently, usually after aggressive braking. Brake fluid, lines and sensors checked normal. Technical bulletin identified a pressure sampling filter algorithm defect in this batch's IPB control unit software, causing false low-pressure warnings under specific conditions. Updated IPB control unit software to latest version via diagnostic tool (version must be higher than V2.3). Continuous testing after upgrade found no further fault codes.
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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.