AU
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) — Qin Plus

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.

The C001404 fault code on the Qin Plus indicates a medium-severity electrical or functional fault in the ABS right front inlet solenoid valve. Common causes include an open or shorted solenoid coil, or a damaged ABS ECU valve driver circuit. Normal braking may still work, but ABS/ESP and AEB may be limited. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1Open circuit or inter-turn short circuit in ABS hydraulic modulator assembly internal right front inlet valve solenoid coil (resistance outside standard range of 2-6Ω)
  • 2Damaged internal solenoid valve drive circuit in the ABS ECU, such as a high-side/low-side driver chip breakdown or cold solder joint.
  • 3Wiring harness connectors (such as X1 and X2 plugs) have backed-out pins, oxidation, or poor contact, interrupting the drive signal.
  • 4Poor connection in the ABS module power supply (constant power B+, ignition IG1) or ground (G101 ground point) circuit, causing a drive voltage drop.
  • 5Prolonged failure to replace the brake fluid causes crystals or contaminants to jam the valve spool, forcing the valve body response to exceed the ECU monitoring threshold.
What To Do
  • 1
    Use a VDS2000 or X431 diagnostic tool to read complete fault codes and freeze-frame data. Record parameters including 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) for looseness or water ingress. Check the brake fluid level and color. Replace the fluid if black or crystallized.
  • 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. This rules out power supply issues 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 the exact pins, typically between two specific pins). The standard value is approx. 2-6 Ω. Compare the reading with the left front inlet valve. If the resistance is infinite or the deviation is >20%, the valve body is faulty.
  • 5
    Inspect the wiring harness connector pins for backing out or oxidation. Measure the 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, test the ABS ECU drive circuit (requires specialized equipment or substitution testing). Because the solenoid valve and ECU come 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

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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

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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 Qin Plus 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.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.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.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus 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.