AU
C000104

DTC C000104 indicates a functional fault in Inlet Valve 1 (circuit control valve) inside the ESP (Electronic Stability Program) hydraulic modulator — Seal U

Braking System

DTC C000104 indicates a functional fault in Inlet Valve 1 (circuit control valve) inside the ESP (Electronic Stability Program) hydraulic modulator.

This solenoid valve controls brake fluid flow from the main brake line to the corresponding wheel cylinder and serves as a key actuator for ESP wheel cylinder pressure regulation.

Root causes include an open or short circuit in the solenoid coil, mechanical sticking of the valve spool, or ECU internal drive circuit failure.

This fault prevents the ESP from independently regulating pressure in this circuit during emergency avoidance maneuvers or skidding.

As a result, the vehicle loses yaw moment control, although conventional hydraulic braking remains functional.

The valve is a non-serviceable component because it integrates with the ECU inside the hydraulic modulator assembly and involves high-pressure brake fluid sealing.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1ESP hydraulic modulator internal solenoid valve coil burnt out or open circuit: Overdue brake fluid replacement increases conductivity, or coil aging and overheating damages the insulation.
  • 2Valve spool mechanically stuck: Metal debris in the brake fluid, aging rubber seal residue, or moisture-induced corrosion prevents the valve spool from returning.
  • 3Hydraulic modulator ECU internal driver chip fault: Voltage fluctuations, overheating, or water ingress damaged the power MOSFET or driver circuit, preventing drive current supply to the solenoid valve.
  • 4Loose or oxidized wiring harness connectors: Loose or burnt pins in the wiring harness for the hydraulic modulator main power supply or solenoid valve drive cause the drive voltage to drop below the operating threshold.
  • 5Severely contaminated brake fluid or excessive water content: Prolonged use without replacement alters the chemical properties of the brake fluid, generating deposits that block precision clearances in the valve body.
What To Do
  • 1
    Diagnostic tool deep scan: Use VDS or Launch X-431 to read all fault codes. Confirm whether C000104 is a Current or History code. Record key parameters from the freeze frame data, such as vehicle speed and yaw rate.
  • 2
    Basic circuit check: Disconnect the hydraulic modulator connector. Measure the pin supply voltage (should be 10-16V) and ground resistance (should be less than 1Ω). Check the 25A/40A fuse continuity and contact resistance.
  • 3
    Solenoid valve actuation test: Connect the diagnostic tool and perform the 'Component Actuation Test'. Listen for a clear clicking sound from Circuit Control Valve 1. If there is no sound or the sound is faint, the internal solenoid valve is faulty.
  • 4
    Brake fluid quality inspection: Draw a brake fluid sample to check color and water content. If the fluid is cloudy dark brown or the water content exceeds 3%, replace the brake fluid and flush the lines.
  • 5
    Assembly replacement procedure: Replace the ESP hydraulic modulator assembly with ECU (part number must match vehicle configuration). Disconnect the battery before replacement. Mark the brake fluid pipes during removal to prevent incorrect installation.
  • 6
    System bleeding and calibration: Bleed the four wheel cylinders according to the standard procedure. Use the diagnostic tool to perform 'Sensor Calibration' (G-Sensor, steering wheel angle sensor) and 'Hydraulic Modulator Fill Status Learning'. Clear the ECU adaptive learning values.
  • 7
    Function verification: After clearing the fault code, perform a road test of at least 20 km on a dry road. Simulate ABS activation (emergency braking) and ESP intervention (high-speed lane change). Confirm the warning lamp is off and the valve body drive current in the data stream is within the normal range (typically 0.5-1.5 A).
Real-World Cases
BYD DTC AI Analysis

BYD Qin Pro: ESP Hydraulic Modulator Left Front Valve Body Fault

✓
Symptoms: ESP/ABS warning light suddenly lit up while driving; abnormal pedal vibration during emergency braking. Diagnosis: Read DTCs C001104 (left front outlet valve) and C001004 (left front inlet valve) together; checked wheel speed sensors—normal; measured hydraulic modulator supply at 12.4V—normal; ran actuator test, left front inlet and outlet valves silent. Determined internal solenoid sticking. Solution: Replaced ESP hydraulic modulator assembly with integrated ECU, performed brake bleeding, sensor calibration, and fill status learning. Road tested 20 km; fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Song DM ABS Return Pump Motor Fault (Water Wading Case)

✓
Symptoms: ABS warning light stays on after startup and flashes when speed exceeds 30 km/h; ABS inoperative. Diagnosis: Retrieved fault code C002004 (return pump motor fault). Component test showed no operating sound from the return pump. Measured infinite resistance across the motor, confirming an open circuit. History revealed water wading six months prior; water entered the hydraulic modulator and corroded the motor internally. Repair: Replaced ABS hydraulic modulator assembly with integrated ECU. Replaced brake fluid (moisture content exceeded specifications). Repaired wiring harness connectors corroded by water exposure.
Original source ↗
BYD DTC AI Analysis

BYD Tang ESP solenoid valve relay intermittent fault

✓
Symptoms: ESP/ABS warning lights came on intermittently during high-speed driving, sometimes clearing after restart with no predictable pattern. Diagnosis: Read DTC C012104 (solenoid valve relay circuit fault), status history/intermittent. Checked power supply circuit; voltage normal but dropped below 7V momentarily on bumps. Found ESP hydraulic modulator main power connector pins loose with internal oxidation; measured contact resistance 3-8Ω (normal <0.5Ω). Resolution: Cleaned connector and applied conductive grease, replaced power harness connector (pin spring tension lost), tightened retaining clips. Road tested 50 km; fault did not recur.
Original source ↗
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.