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) — Atto 3

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.

4
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Open circuit or inter-turn short circuit in the ABS hydraulic modulator assembly internal right front inlet valve solenoid coil (resistance deviates from standard value of 2-6 Ω)
  • 2Damaged internal solenoid valve drive circuit in the ABS ECU, such as high-side/low-side driver chip breakdown or cold solder joints.
  • 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 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 a VDS2000 or X431 diagnostic tool to read the 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 exterior of the ABS hydraulic modulator assembly for leaks. Check the wiring harness connectors (especially those related to the right front) for looseness or water ingress. Check the brake fluid level and color. Replace the brake fluid if it is 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 insufficient drive capability caused by a power supply fault.
  • 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 wiring diagram for the exact pins, typically between two specific pins). The standard value is approx. 2-6Ω. 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
    Check 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 using 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 actuate 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 Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.