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 — Seal U

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 Seal U indicates a medium-severity fault with the right rear wheel outlet valve inside the ABS hydraulic modulator. This can stop proper brake pressure release during ABS operation and may disable ABS, EBD, and ESC warning functions. Common causes include a faulty solenoid coil, wiring short/open circuit, or ABS ECU driver fault. The recommended fix is diagnosis and repair by an authorised dealer. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 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 driver chip, burnt power MOSFET, or cold solder joint)
  • 3Brake fluid contamination, deterioration, or impurities cause a stuck solenoid valve spool, swollen sealing ring, or blocked hydraulic passage.
  • 4Water ingress, oxidation, corrosion, or pin 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 grounding resulting in insufficient solenoid valve drive current
What To Do
  • 1
    Use the dedicated BYD diagnostic tool (VDS or ED400) to read all fault codes. Confirm C001D04 is a current fault and cannot be cleared. Record the freeze frame data.
  • 2
    Check the ABS system power supply: Measure the voltage at the ABS ECU power pin. The voltage must be within 9-16V (normally approx. 12.5V). Check the fuse, relay, and power wiring.
  • 3
    Check the ground system: Measure the resistance between the ABS ECU ground wiring harness and the body ground. The 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 clear clicking sound. If no sound occurs, diagnose a mechanical or electrical fault in the internal solenoid valve.
  • 6
    Check the brake fluid level, quality, and color. If necessary, extract brake fluid to check for metal debris or gel-like contaminants.
  • 7
    If confirming the fault is inside the hydraulic modulator, replace the ABS hydraulic modulator assembly (with 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 (requires dedicated bleeding equipment or manual bleeding). Use a diagnostic tool to perform system calibration, check wheel speed sensor signals, and verify via 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 Seal U Fault Codes
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.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.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.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.