UK
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.

5
Cases Logged
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
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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.