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 8

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 Atto 8 indicates a medium-severity electrical or functional fault in the right front ABS inlet solenoid valve. Common causes include an open or shorted solenoid coil in the ABS hydraulic modulator, or a damaged ABS ECU valve driver circuit. Normal braking should remain, but ABS/ESP may be disabled. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 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 2-6Ω)
  • 2Damaged solenoid valve drive circuit inside the ABS ECU (e.g., high-side/low-side driver chip breakdown or dry solder joint).
  • 3Backed-out pins, oxidation, or poor contact at harness connectors (such as X1 and X2 plugs) interrupts 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.
  • 5Overdue brake fluid replacement leads to crystallization or contaminants jamming the valve spool, causing the valve body operating 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 such as vehicle speed, wheel speed, and battery voltage. Clear the fault codes and road test the vehicle (including braking at speeds above 30 km/h) to determine if the fault is intermittent.
  • 2
    Visually inspect the ABS hydraulic modulator assembly for leaks. Check the wiring harness connectors (especially the front right) for looseness or water ingress. Check the brake fluid level and color. Replace the fluid if it is black or crystallized.
  • 3
    Measure the power supply voltage at the ABS pump electrical connector: constant power (B+) should be 12 V, ignition signal (IG1) should be ≥12 V when ON, and ground resistance should be <1 Ω. Rule out power supply issues causing insufficient drive capability.
  • 4
    Disconnect the ABS pump harness connector. Use a multimeter to measure the right front inlet valve solenoid coil resistance (refer to the E5 wiring diagram for specific pins, typically between two designated pins). Standard value: approximately 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
    Check the wiring harness connector pins for push-out or oxidation. Measure circuit continuity between the valve body pins and the ABS ECU internal drive circuit to rule out a wiring harness open or short circuit.
  • 6
    If solenoid valve resistance is normal but the fault code persists, check the ABS ECU drive circuit using professional equipment or substitution testing. Because the solenoid valve and ECU form 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 for assisted bleeding), calibrate the wheel speed sensor signal, calibrate the yaw rate sensor zero point, and road test the vehicle 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 Atto 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.