AU
C000204

This DTC indicates an electrical fault (typically an open circuit or abnormal resistance) in Circuit Control Valve 2 inside the ESP (Electronic Stability Program) hydraulic modulator — Seal U

Braking System

This DTC indicates an electrical fault (typically an open circuit or abnormal resistance) in Circuit Control Valve 2 inside the ESP (Electronic Stability Program) hydraulic modulator.

During active ESP braking intervention, this solenoid valve precisely controls the build-up and release of hydraulic pressure in a specific brake circuit (typically the rear wheel brake circuit).

When this fault triggers, the ESP system enters degraded mode and disables electronic stability control, traction control (TCS), and automatic emergency braking (AEB).

The vehicle typically retains conventional hydraulic braking.

This is a hardwired circuit fault, not a software false positive.

Focus inspection on the solenoid valve coil integrity and the ECU driver circuit.

The C000204 fault code on the Seal U indicates an electrical fault in Circuit Control Valve 2 inside the ESP hydraulic modulator. Severity is medium: normal hydraulic braking usually remains, but ESP, traction control, and AEB may be disabled. Common causes include an open or high-resistance solenoid valve coil, or corrosion/loose pins at the modulator connector. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Open circuit or excessive resistance in the internal solenoid valve coil of the ESP hydraulic modulator assembly (normal range is typically 12-25Ω; refer to the vehicle repair manual for exact specifications).
  • 2Oxidation, looseness, or corrosion from water ingress at the hydraulic modulator wiring harness connector pins (usually located on the top or side of the modulator), causing an open circuit.
  • 3Damaged internal valve body drive circuit in the ABS/ESP ECU (e.g., MOSFET power transistor breakdown or open circuit), failing to supply operating current to the valve.
  • 4Power supply circuit fault, including a blown dedicated ABS system fuse (usually 30A-40A) or poor contact in the power supply wiring harness.
  • 5Poor or broken solder joints on the hydraulic modulator internal flexible printed circuit board (FPC) or coil pins
What To Do
  • 1
    Use the BYD VDS2000/VDS3000 diagnostic tool to read the complete fault code stream and freeze frame data. Verify the vehicle speed, voltage, and other operating conditions at the time of the fault to rule out intermittent faults.
  • 2
    Disconnect the 12V battery negative terminal, remove the ESP hydraulic modulator assembly (located at the front left or front right of the engine compartment, with brake lines), and check the exterior for impact damage, leaks, or burn marks.
  • 3
    Measure the resistance at the corresponding pins of the hydraulic modulator wiring harness connector (refer to the E5 circuit diagram, typically the valve body drive pins) and compare it to the standard value (approximately 12-25 Ω). Infinite resistance confirms an open circuit in the valve body coil.
  • 4
    Check wiring harness continuity: Measure continuity of the wiring harness between the ECU and the valve body. Check for open circuits, shorts to ground, or shorts to power. Focus on the firewall grommet and harness bends at the connectors.
  • 5
    Perform the valve body active test: Reconnect the diagnostic tool. With the ignition switch in the ON position, perform the 'Circuit Control Valve 2' active test. Listen for a distinct engagement click and use an oscilloscope to observe the drive current waveform (normally a sawtooth wave, peak approx. 1.5-2A).
  • 6
    If circuit measurements are normal but the valve body does not operate, replace the ESP hydraulic modulator assembly with ECU (refer to the E5 brake system BOM for the part number). After replacement, perform the brake system bleeding and sensor calibration procedures.
  • 7
    Clear the fault codes and perform a road test (including straight-line acceleration, emergency braking, and cornering) to confirm the ESP function operates normally and no new fault codes appear.
Real-World Cases
BYD DTC AI Analysis

High-frequency use caused the valve body coil to age and develop an open circuit in the E5 taxi.

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Vehicle: 2018 BYD E5, 280,000 km. Symptoms: ABS and ESP warning lights on constantly. Retrieved fault code C000204. Diagnosis: Measured resistance between hydraulic modulator harness connector pins B05-12 and B05-13 (circuit control valve 2 drive terminals): open circuit (specification 15Ω). Confirmed coil break inside valve body. Disassembled hydraulic modulator; internal solenoid coil magnet wire burned out from overheating due to prolonged high-frequency operation. Solution: Replaced ESP hydraulic modulator assembly with integrated ECU (part number: C000204-compatible model). Bled brakes and calibrated yaw rate sensor after replacement. Fault resolved.
BYD DTC AI Analysis

Driving through water corroded the wiring harness connector, causing intermittent faults.

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Model: 2019 BYD E5. Symptoms: ESP warning light illuminates intermittently after driving in rain; clears after restarting. DTC C000204 stored as a history code. Diagnosis: Valve body resistance normal in dry conditions. Simulated water spray test showed fluctuating resistance between pins 9 and 10 of connector B05 (0.5–50Ω). Disassembled connector and found degraded seal and green copper oxide on pin surfaces. Repair: Cleaned harness connector pins, applied electronic-grade protective silicone grease, replaced seal, and re-secured waterproof cover. Follow-up: Monitored for one month; no recurrence.
BYD DTC AI Analysis

ECU internal driver circuit damage prevented the valve from energizing.

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Vehicle: 2018 BYD E5. Issue: C000204 DTC set after brake fluid replacement. Diagnosis: External harness continuity normal; valve body resistance 14.5Ω (normal); power supply 12.5V (normal). During active testing, oscilloscope showed no drive voltage waveform at the ECU output. ABS ECU internal valve body driver chip damaged—likely from backflow impact during improper brake bleeding. Fix: ECU and hydraulic modulator are integrated. Replaced ESP hydraulic modulator assembly. Fault cleared. Note: Follow brake fluid replacement specifications strictly. Avoid rapidly pumping the brake pedal to prevent hydraulic shock.
Other Seal U Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.