AU
C001400

C001400 is an ISO 14229 standard fault code — Seal U

Braking System

C001400 is an ISO 14229 standard fault code. 'C' represents the chassis system, '0014' specifies the right front wheel brake line inlet valve, and '00' indicates a General Electrical Failure.

In BYD vehicles equipped with Bosch ESP 9.x or the in-house IPB (Intelligent Integrated Braking System), this fault indicates a circuit malfunction inside the Hydraulic Control Unit (HCU) driving the right front inlet solenoid valve.

Possible causes include an open or short circuit in the solenoid valve coil, a damaged driver stage (MOSFET) on the control circuit board, or abnormal current caused by a sticking valve core.

This fault disables the ABS, ESP, and Automatic Emergency Braking (AEB) functions, but does not affect conventional hydraulic braking.

This safety-related fault requires immediate repair.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1ABS hydraulic control unit (HCU) internal right front inlet solenoid valve coil burnt out or open circuit (internal hardware damage)
  • 2IPB/ESC module internal circuit board driver chip failure (e.g., solenoid valve driver MOSFET breakdown or cold solder joint)
  • 3Poor contact in the ABS pump assembly power supply or ground circuit (oxidation or loose connection at the front compartment wiring harness connector causing unstable voltage)
  • 4Vehicle wading or improper washing causes corrosion and a short circuit in the internal ABS pump circuitry (commonly due to poor connector sealing).
  • 5Overdue brake fluid replacement causes impurities to jam the solenoid valve, resulting in abnormal drive current and triggering fault protection.
What To Do
  • 1
    Use the BYD VDS2000 or Bosch KT770 diagnostic tool to read fault codes. Confirm C001400 and accompanying codes (such as C001100 left front fault), and record freeze frame data (vehicle speed, temperature, etc.).
  • 2
    Visually inspect the ABS pump assembly (located on the left side of the engine compartment or near the firewall) for external leaks, check the connector for water ingress or oxidation, and measure the plug power supply (constant 12V, IGN power) and ground resistance (must be <1Ω).
  • 3
    Disconnect the ABS pump connector and use a multimeter to measure the resistance of the right front inlet valve solenoid coil (normal range: 2-8Ω; infinite or 0Ω indicates internal damage).
  • 4
    Check the CAN line voltage (CAN-H: 2.6V ± 0.2V, CAN-L: 2.4V ± 0.2V) and terminating resistance (approx. 60Ω) to eliminate communication interference.
  • 5
    Actuator Test: Use the diagnostic tool to actuate the right front inlet valve. Listen for a click and observe brake fluid pressure changes. If there is no response, confirm an internal fault.
  • 6
    After confirming the fault, replace the ABS pump assembly (with ESC/IPB module). On some models, replace the brake pipe sealing rings simultaneously. Verify part numbers match before installation.
  • 7
    After replacement, perform the following: ① Bleed the brake system (use the diagnostic tool to drive the motor to bleed air) ② Perform ESC module online coding (write VIN) ③ Calibrate the wheel speed sensor signal ④ Road test to verify ABS function
Real-World Cases
BYD DTC AI Analysis

BYD Song Pro ABS/ESP warning lights illuminated simultaneously while driving

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At 15,000 km, the dashboard suddenly lit the ABS, ESP and tyre pressure warning lights. The dealership used VDS to read fault code C001400 (right front inlet valve fault) along with C001000 (return pump fault). The ABS pump connector showed no abnormalities. The right front inlet valve resistance measured infinite (open circuit), indicating the internal solenoid coil had burned out. Replaced the ABS pump assembly (Bosch ESP 9.3 system), performed brake bleeding and ESC coding, and eliminated the fault.
Original source ↗
BYD DTC AI Analysis

BYD Qin 80 ESP warning after driving through water

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After driving through water, the dashboard displayed “Check ESP System.” Retrieved DTCs C001400 and C001100 (left front inlet valve). The workshop disassembled the ABS pump connector and found traces of muddy water inside. After cleaning, blow-drying, and road testing, the fault disappeared, but it recurred one week later. Determined that the circuit board had corroded during the water crossing, causing an intermittent open circuit in the solenoid valve drive circuit. Replaced the ESC assembly (including HCU) and advised checking water depth before wading to prevent repeat damage.
Original source ↗
BYD DTC AI Analysis

BYD Tang DM – Intermittent ABS Warning Light When Hot

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Cold starts normal. ABS light illuminates after 20 minutes of driving and clears after restart. Thermal imaging of the ABS pump revealed abnormal heating in the right front inlet valve driver circuit area at operating temperature. Valve body resistance drifted from 3Ω to 15Ω when hot. Internal solder joint failed due to thermal expansion. Replaced ABS hydraulic control unit (HCU section). Fault has not recurred.
Original source ↗
BYD DTC AI Analysis

BYD Song PLUS: Loose connector causing false alarm

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ABS light intermittently illuminates on rough roads; DTC C001400 intermittent. ABS pump power supply checks normal, but the connector locking clip is broken, causing poor contact. Cleaned oxidation from the ground point at the left front fender, replaced the ABS pump connector harness (repair kit), then monitored the inlet valve drive waveform with an oscilloscope—stable. Fault resolved. This was a wiring issue, not a pump failure, avoiding unnecessary ABS pump replacement.
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.