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C001404

DTC C001404 indicates an electrical fault or functional abnormality in the inlet solenoid valve (normally open valve, NO Valve) controlling the right front brake wheel cylinder within the ABS (Anti-lock Braking System) Hydraulic Control Unit (HCU) — Seal 6 EV

Braking System

DTC C001404 indicates an electrical fault or functional abnormality in the inlet solenoid valve (normally open valve, NO Valve) controlling the right front brake wheel cylinder within the ABS (Anti-lock Braking System) Hydraulic Control Unit (HCU).

During normal braking, this solenoid valve remains open to allow brake fluid into the wheel cylinder.

When ABS activates, the ECU rapidly closes the valve to regulate pressure.

Root causes include an open or short circuit in the solenoid valve coil, a failed ABS ECU internal drive circuit (MOSFET or intelligent power chip), a stuck valve spool causing a response timeout, or abnormal wiring connections.

This fault disables the ABS/ESP functions, though normal hydraulic braking remains available.

Emergency braking carries a risk of right front wheel lockup, and the system may limit the Automatic Emergency Braking (AEB) function.

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Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Open circuit or inter-turn short circuit in the right front inlet valve solenoid coil inside the ABS hydraulic modulator assembly (resistance deviates from the standard value of 2-6 Ω).
  • 2Damaged ABS ECU internal solenoid valve drive circuit, such as high-side/low-side driver chip breakdown or a cold solder joint.
  • 3Wiring harness connectors (such as X1 and X2 plugs) have recessed pins, oxidation, or poor contact, interrupting the drive signal.
  • 4Poor contact in the ABS module power supply (constant B+, ignition IG1) or ground (G101 ground point) circuit, causing a drive voltage drop.
  • 5Prolonged failure to replace the brake fluid causes crystallization or contaminants to jam the valve spool, causing the valve body response to exceed the ECU monitoring threshold.
What To Do
  • 1
    Use the VDS2000 or X431 diagnostic tool to read the complete fault codes and freeze frame data. Record parameters such as vehicle speed, wheel speed, and battery voltage. Clear the fault codes and road test the vehicle (including braking above 30 km/h) to confirm if the fault is intermittent.
  • 2
    Visually inspect the ABS hydraulic modulator assembly for leaks. Check the wiring harness connectors (especially the right front connectors) for looseness or water ingress. Check the brake fluid level and colour (replace the fluid if black or crystallised).
  • 3
    Measure the power supply voltage at the ABS pump electrical connector: constant power (B+) should be 12V, ignition signal (IG1) should be ≥12V when ON, and ground resistance should be <1Ω. Rule out power supply faults causing insufficient drive capability.
  • 4
    Disconnect the ABS pump wiring harness connector. Use a multimeter to measure the right front inlet valve solenoid coil resistance (refer to the E5 circuit diagram for specific pins, typically between two designated pins). Standard value: approx. 2-6Ω. Compare the reading with the left front inlet valve. An infinite resistance or a deviation >20% indicates a faulty valve body.
  • 5
    Inspect the wiring harness connector pins for backing out or oxidation. Measure circuit continuity between the valve body pins and the ABS ECU internal drive circuit to rule out an open or short circuit in the wiring harness.
  • 6
    If solenoid valve resistance is normal but the fault code persists, check the ABS ECU drive circuit (requires specialized equipment or substitution testing). Since the manufacturer typically supplies the solenoid valve and ECU as an integrated unit, replace the complete ABS hydraulic modulator assembly.
  • 7
    After replacing the assembly, perform the following: bleed the brake lines (use the diagnostic tool to drive the motor pump to assist bleeding), calibrate the wheel speed sensor signal, calibrate the yaw rate sensor zero point, and perform a road test to verify ABS function.
Real-World Cases
BYD DTC AI Analysis

2018 E5: Open circuit in ABS pump solenoid coil causing C001404

✓
ABS and ESP warning lights constantly illuminated on the instrument panel. Retrieved DTC C001404. Measured infinite resistance between right front inlet valve pins at ABS pump connector (normal ~3.5Ω); left front inlet valve tested normal. Diagnosed open circuit in right front inlet valve coil inside ABS hydraulic modulator. Replaced ABS assembly; fault resolved.
BYD DTC AI Analysis

Oxidized wiring harness connector caused intermittent C001404 fault

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ABS warning light illuminated intermittently while driving and cleared after stopping and restarting. Scanner showed C001404 as a history fault. Found green oxidation on the pins inside ABS pump harness connector X1, causing fluctuating contact resistance. Cleaned the pins, applied conductive grease, and secured the harness to prevent vibration. Fault has not recurred.
BYD DTC AI Analysis

Crystallized brake fluid jammed the inlet valve

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2019 E5, 50,000 km without brake fluid change. Instrument cluster displayed brake system fault. DTC C001404. Solenoid resistance normal, but right front inlet valve made no sound during actuator test. Disassembled ABS pump: white crystals inside valve body from brake fluid moisture absorption. Replaced ABS assembly and all brake fluid, flushed lines. Resolved.
BYD DTC AI Analysis

Replaced ABS ECU assembly due to drive circuit damage

✓
DTC C001404 set along with C001500 (right front outlet valve fault). Resistance normal on both valves; wiring harness checked OK. Found ABS ECU internal driver chip (L9369 or similar) damaged, unable to drive right front solenoid valve. Replaced ABS hydraulic modulator assembly, completed programming/matching; fault eliminated.
Other Seal 6 EV 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.