AU
C05C200

DTC C05C200 indicates the electric booster motor operating temperature in the IPB (Intelligent Power Brake) integrated brake system exceeds the safety threshold (typically 120°C–130°C) — Seal U

Braking System

DTC C05C200 indicates the electric booster motor operating temperature in the IPB (Intelligent Power Brake) integrated brake system exceeds the safety threshold (typically 120°C–130°C).

The IPB system uses a brushless DC motor to drive the brake master cylinder and generate hydraulic boost, completely replacing the traditional vacuum booster.

When the motor temperature sensor (NTC thermistor) detects an abnormal temperature rise in the motor windings or drive module, the ECU stores this DTC and initiates a protection strategy.

This strategy limits motor power output, illuminates the ABS/ESC warning light, and may switch the system to a degraded mode (no boost or hydraulic brake backup).

This fault results in a noticeably harder brake pedal, increases required pedal force, and extends braking distance, posing a severe safety hazard during continuous braking or high-speed driving.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Brake drag or poor return: Brake caliper piston corrosion, seized guide pins, or incorrect brake pad installation causes continuous clamping. The motor operates continuously to maintain pressure, generating excessive heat.
  • 2Cooling system fault: Mud or sand blocking the cooling air duct at the IPB module installation location, poor heat dissipation inside the compartment, or sustained high ambient temperatures (e.g., prolonged aggressive driving or towing mode).
  • 3Abnormal mechanical load: Degraded or water-contaminated brake fluid increasing master cylinder piston resistance, partial brake line blockage, or motor bearing wear reducing transmission efficiency.
  • 4Control strategy defect: Outdated IPB ECU software version, abnormal motor PWM control duty cycle, or improper stall protection threshold setting causes the motor to operate at full load for extended periods.
  • 5Motor assembly fault: Motor winding insulation aging (insulation resistance <1MΩ), abnormal Hall sensor signal, or drive MOSFET overheating, reducing energy conversion efficiency and generating Joule heat.
What To Do
  • 1
    Freeze frame analysis: Use VDS2000 or a dedicated diagnostic tool to read freeze frame data from when the fault occurred, including ambient temperature, motor temperature, brake pressure, and motor current, to verify a true overheat condition rather than a false sensor reading.
  • 2
    Visual and cooling inspection: Inspect the IPB module for impact damage, clean dust and oil from the heat sink surface, and verify the mounting bracket is free of deformation causing poor contact with the cooling surface.
  • 3
    Brake system drag check: Raise the vehicle, shift to N, and manually rotate all four wheels to check for binding. Press and release the brake pedal, observe if the brake pads return promptly, and measure the residual brake drag.
  • 4
    Electrical verification: Disconnect the IPB wiring harness. Measure the motor temperature sensor resistance (approximately 10 kΩ at 25°C) and compare it against the temperature-resistance curve. Measure the motor three-phase winding resistance balance (deviation <5%) and insulation resistance to ground (>20 MΩ).
  • 5
    Hydraulic system check: Extract brake fluid and check for black discoloration or impurities. Verify the brake master cylinder piston slides smoothly. If necessary, replace the brake fluid and bleed the system (use dedicated bleeding equipment).
  • 6
    Software update and calibration: Check the IPB ECU software version and update to the latest version (such as the optimized thermal management strategy version released after 2023); perform brake pressure sensor calibration and motor zero-position learning.
  • 7
    Assembly replacement: If motor insulation resistance is <1 MΩ, drive current remains >18 A (normal idle <5 A), or the system frequently sets the fault code despite normal heat dissipation, replace the IPB electro-hydraulic module assembly with ECU, then complete coding and system bleeding.
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i IPB overheat protection activates during prolonged downhill braking

✓
After 15 km of continuous downhill, the ABS and ESC warning lights lit up and the brake pedal stiffened. Scanner read DTC C05C200; freeze frame showed motor temperature at 138°C. Inspection found no brake drag and the heat sink normal. Continuous braking kept the motor running constantly, causing heat buildup. Fix: Updated IPB software to latest version (optimized thermal management for long downhills, added intermittent motor operation). Advised driver to use regenerative braking (high recuperation mode) together with braking, avoiding continuous heavy pedal application. Fault has not recurred.
BYD DTC AI Analysis

Contaminated brake fluid caused master cylinder sticking, leading to motor overheating

✓
Came in for routine service with the IPB warning light on. Scanned DTC C05C200. Found brake fluid severely blackened (water content >4%) and master cylinder piston sliding resistance significantly increased. Disassembled the IPB; internal piston seals were swollen and deformed. The contaminated, high-viscosity fluid forced the motor to draw excessive current—22A measured against a normal 10A—to drive the master cylinder, causing rapid temperature rise. Replaced the IPB assembly (internal piston worn), flushed the brake lines thoroughly, refilled with DOT4 low-viscosity brake fluid, and bled the system. Advised customer to replace brake fluid every 2 years.
BYD DTC AI Analysis

Blocked IPB heat sink caused false motor overheat warning

✓
During hot summer weather, the owner reported the warning light illuminated after one hour of congested urban driving, clearing after the vehicle cooled. Inspection found the IPB mounted beneath the battery with cooling fins completely blocked by lint and dust, severely reducing heat exchange. Infrared thermometer measured motor housing temperature at 125°C (normal: <80°C). Resolution: Thoroughly cleaned the cooling fin air ducts, installed a heat insulation pad beneath the IPB to prevent battery heat radiation, and advised the owner to check the engine bay regularly for cleanliness. Tracked for one month after cleaning—fault has not returned.
BYD DTC AI Analysis

False alarm caused by temperature sensor drift

✓
The vehicle set a C05C200 fault code immediately on cold start. Ambient temperature was only 15°C — the motor could not possibly be overheating. Measured the temperature sensor resistance and found only 3kΩ at room temperature (corresponding to approximately 60°C), seriously deviating from the standard curve (10kΩ@25°C). Sensor drift caused the ECU to falsely detect motor overheat. Further inspection revealed oxidised and corroded pins on the IPB wiring harness (the vehicle had previously been driven through water). Solution: Cleaned the wiring harness pins, applied conductive paste, and replaced the temperature sensor. Since the sensor is integrated inside the IPB, this required replacing either the entire motor assembly or the IPB assembly. After replacement the fault code cleared and the data stream showed normal temperature.
BYD DTC AI Analysis

Frequent ESC intervention overloaded the power steering motor

✓
Customer reported the warning light came on after driving on icy winter roads. Diagnosis revealed DTC C05C200 accompanied by C005108 (steering angle sensor fault). Steering angle signal drift caused the ESC to falsely detect instability, triggering continuous active braking (frequent hydraulic pump cycling) and overheating the assist motor. Inspection found the steering angle sensor mounting position was offset. Fix: Recalibrated the steering angle sensor (neutral position adjustment), updated ESC control logic (software upgrade), and performed a cooling reset on the IPB. Advised the customer to stop and rest the vehicle if warnings appear after extreme road conditions.
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.