AU
C001D04

This DTC indicates an electrical or mechanical fault in the right rear wheel outlet valve (discharge valve/release valve) inside the ABS (Anti-lock Braking System) hydraulic modulator assembly — Atto 8

Braking System

This DTC indicates an electrical or mechanical fault in the right rear wheel outlet valve (discharge valve/release valve) inside the ABS (Anti-lock Braking System) hydraulic modulator assembly.

This solenoid valve is a key actuator in the ABS hydraulic unit and controls the release of hydraulic pressure from the right rear wheel brake caliper during the ABS activation cycle.

The ECU sets this DTC when it detects an open circuit, short circuit, short to ground, or short to power in the solenoid valve circuit, or when the valve spool fails to open or close normally due to mechanical sticking.

This fault causes the right rear wheel ABS pressure regulation function to fail.

During emergency braking, the right rear wheel may fail to release pressure normally (causing premature lock-up) or retain pressure abnormally, severely affecting braking stability and safety.

The system enters fail-safe mode, disables the ABS, EBD, and ESC functions, and illuminates the relevant warning lamps.

The C001D04 fault code on the Atto 8 indicates a fault with the right rear wheel outlet valve inside the ABS hydraulic modulator. Severity is medium because it can disable ABS, EBD, and ESC, affecting braking stability during emergency braking. Common causes include a faulty solenoid coil or a damaged ABS ECU valve driver circuit. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Open circuit, short circuit, or resistance drift in the right rear wheel outlet valve solenoid coil inside the ABS hydraulic modulator assembly.
  • 2Damaged ABS ECU internal solenoid valve drive circuit (e.g., burnt-out driver chip or power MOSFET, or cold solder joint)
  • 3Brake fluid contamination, degradation, or impurities causing solenoid valve spool binding, sealing ring swelling, or hydraulic circuit blockage.
  • 4Water ingress, oxidation, corrosion, or terminal back-out at the wiring harness connector causes poor contact in the solenoid valve control circuit.
  • 5Abnormal system power supply voltage (below 9V or above 16V) or poor ground causes insufficient solenoid valve drive current.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS or ED400) to read all fault codes, confirm C001D04 is a current fault that will not clear, and record the freeze frame data.
  • 2
    Check the ABS system power supply: Measure the voltage at the ABS ECU power pins. The voltage must be 9-16V (normally about 12.5V). Check the fuses, relays, and power supply wiring.
  • 3
    Check the ground system: Measure the resistance between the ABS ECU ground harness and the body ground. Resistance must be less than 1 Ω. Check the ground point for looseness or oxidation.
  • 4
    Disconnect the ABS ECU connector and visually inspect the right rear wheel outlet valve control pin (refer to the wiring diagram for the specific pin number) for signs of water ingress, corrosion, or burn marks.
  • 5
    Perform the solenoid valve active test (actuation test): Use the diagnostic tool to trigger the right rear wheel outlet valve and listen for a crisp clicking sound. If no sound occurs, the internal solenoid valve has a mechanical or electrical fault.
  • 6
    Check the brake fluid level, quality, and color. If necessary, extract brake fluid to check for metal debris or gelatinous contaminants.
  • 7
    If the fault is inside the hydraulic modulator, replace the ABS hydraulic modulator assembly (including the ECU, as BYD models usually do not support separate solenoid valve replacement).
  • 8
    After installing the new assembly, bleed the brake lines according to the standard procedure (using dedicated bleeding equipment or manual bleeding). Use the diagnostic tool to perform system calibration, check wheel speed sensor signals, and verify with a road test.
Real-World Cases
BYD DTC AI Analysis

BYD Qin ABS solenoid valve internal open circuit fault

✓
ABS and ESP warning lights remained on. Owner reported abnormal brake feel at the right rear wheel. Scan tool retrieved fault code C001D04 (right rear outlet valve fault). Battery voltage measured 12.4V – normal. ABS ECU ground connection secure. Vehicle sat for 10 minutes; rescanned – fault code still present. Performed solenoid activation test – no actuation sound from right rear outlet valve. Measured internal solenoid resistance: open circuit. Diagnosed as internal ABS ECU solenoid failure. Replaced ABS hydraulic modulator assembly and performed bleeding calibration. Fault completely resolved.
Original source ↗
BYD DTC AI Analysis

BYD e5 Pure Electric Vehicle ABS Hydraulic Unit Failure

✓
The dashboard displayed "Check ABS System" and the ABS warning light stayed on. The right rear wheel locked up during emergency braking tests. Scanned with a diagnostic tool and retrieved DTC C001D04. Checked HV system insulation — normal. Ruled out HV interference. Measured 12V supply — normal. Swapped left and right rear wheel speed sensors; DTC still pointed to right rear outlet valve. Confirmed internal solenoid valve fault in ABS hydraulic control unit. Replaced ABS assembly and completed system configuration. ABS function returned to normal.
Original source ↗
BYD DTC AI Analysis

BYD Song ABS Pump Solenoid Valve Sticking

✓
ABS warning light suddenly illuminated while driving. When vehicle speed exceeded 40 km/h, slight chassis vibration developed. Connected a scan tool and retrieved DTC C001D04 (right rear outlet valve fault). Inspected right rear wheel speed sensor and wiring connections; normal. Brake fluid level normal. Performed solenoid valve actuation test via scan tool: right rear outlet valve showed no response, other wheel solenoids operated normally. Measured solenoid resistance: infinite (open circuit). Determined internal ABS pump assembly solenoid had failed. Replaced ABS pump assembly; fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD F3 ABS ECU internal drive circuit fault

✓
After starting the vehicle, the ABS warning light stayed on, with intermittent beeping while driving. Connected an OBD scanner and retrieved fault code C001D04. Inspected the ABS fuse and relay; both functioned correctly. Checked the right rear wheel cylinder and hydraulic lines and found no leaks. Verified the vehicle had no history of overheating, ruling out false triggers from thermal protection. Used an oscilloscope to check the solenoid valve drive signals; the ECU was not outputting a drive waveform. Isolated the fault to an internal drive circuit failure in the ABS ECU. Replaced the ABS electronic control unit assembly, cleared the fault code, and restored system functionality.
Original source ↗
BYD DTC AI Analysis

Abnormal ABS power supply caused solenoid valve failure in BYD models

✓
ABS warning light on with DTCs C001D04 and C0121 (solenoid valve relay fault) stored. With the vehicle stationary, heard abnormal solenoid valve relay chattering. Measured ABS solenoid valve supply voltage at only 9.5V (low). Checked ABS fuse holder: poor contact with slight burn marks. Cleaned fuse holder and tightened ground; voltage returned to normal, C0121 cleared, but C001D04 remained. Further testing confirmed right rear outlet valve failure. Replaced ABS assembly. Resolved.
Original source ↗
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.