AU
C001104

DTC C001104 indicates a circuit or functional fault in the left front wheel outlet valve (LF Outlet Valve) inside the ABS (Anti-lock Braking System) Hydraulic Electronic Control Unit (HECU) assembly — Seal U

Braking System

DTC C001104 indicates a circuit or functional fault in the left front wheel outlet valve (LF Outlet Valve) inside the ABS (Anti-lock Braking System) Hydraulic Electronic Control Unit (HECU) assembly.

This solenoid valve integrates into the ABS pump body.

During the ABS pressure reduction phase, it returns high-pressure brake fluid from the left front brake caliper to the reservoir or master cylinder, rapidly reducing wheel cylinder pressure and preventing wheel lock-up.

Fault trigger conditions include an open or short circuit in the solenoid coil, a mechanically stuck valve core, a damaged internal ABS ECU driver circuit (MOSFET), or an open or short circuit in the control wiring.

This fault disables the left front wheel ABS pressure reduction function.

During emergency braking, this wheel may lock up prematurely, causing the vehicle to pull or lose directional control and severely compromising driving safety.

The C001104 fault code on the Seal U indicates a medium-severity fault with the left front ABS outlet valve inside the hydraulic control unit. This can stop ABS pressure reduction at that wheel, increasing lock-up risk during hard braking. Common causes include a failed or stuck solenoid valve, damaged ABS pump connector pins, or poor wiring. Have the vehicle checked by an authorised dealer. Typical repair cost data is available from recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Open or short circuit in the left front outlet valve solenoid coil, or stuck valve spool inside the ABS hydraulic modulator assembly (internal mechanical fault)
  • 2Oxidized, loose, or backed-out pins at the ABS pump connector, or a poor wiring harness connection, interrupting the solenoid valve power supply (pin 25) or control signal.
  • 3Damaged ABS ECU internal solenoid valve drive circuit (e.g., burnt driver chip), failing to output approximately 12V drive current to the solenoid valve.
  • 4Solenoid valve power supply circuit fault, including a blown 25A ABS fuse in the engine compartment, poor contact at the fuse holder, or excessive resistance in the ground circuit (pin 38).
  • 5Interference or short circuit in the associated wiring (e.g., damaged left front wheel speed sensor harness shorted to ground), causing the ECU to misinterpret the solenoid valve circuit status.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS2000/VDS2100) to read the fault code. Verify C001104 is present and review the freeze frame data to confirm the vehicle speed and system status at the time of the fault.
  • 2
    Run the ABS system 'Actuator Test', select the left front outlet valve (LF Outlet Valve), and listen for a clear 'click' to determine if the solenoid valve actuates normally.
  • 3
    Perform a visual inspection: Check the ABS hydraulic modulator connector (usually a 25-pin or 38-pin black plug) for looseness, and inspect pin 25 (solenoid valve power supply) and pin 38 (ground) for oxidation, burn marks, or brake fluid contamination.
  • 4
    Measure the solenoid valve supply voltage: Turn the ignition switch to ON. Use a multimeter to measure the voltage between connector pin 25 and ground. The standard value is 10-16V. Also inspect the 25A ABS fuse and base in the engine compartment fuse box for burning or deformation.
  • 5
    Measure solenoid valve coil resistance: Disconnect the ABS pump connector. Use a multimeter to measure the resistance between the left front outlet valve drive terminals. The normal value is typically 5-10 Ω (refer to the vehicle repair manual for exact specifications). Infinite resistance indicates a coil open circuit; 0 Ω indicates a coil short circuit.
  • 6
    Perform a circuit continuity check: Use a multimeter to measure the continuity of the left front outlet valve control wire between the ABS ECU connector and the pump body connector to rule out an open circuit or high resistance. Use an oscilloscope or breakout box to monitor voltage stability while driving to rule out intermittent poor contact.
  • 7
    If wiring and resistance are normal but the component test fails, or if the fault transfers after swapping the ABS pump assembly from a known good vehicle, this indicates an internal ABS pump assembly fault (solenoid valve or ECU drive circuit). Replace the ABS hydraulic modulator assembly with ECU (Note: the solenoid valve is not serviceable separately).
  • 8
    After replacement, perform the brake system bleeding procedure (use the diagnostic tool to execute 'Bleeding Mode' to activate the fluid pump). Clear the fault codes and perform a road test (exceed 30km/h and maintain this speed for over 10 seconds to trigger the ABS self-check). Confirm the system operates normally and the fault light is off.
Real-World Cases
BYD DTC AI Analysis

BYD Qin - ABS Pump Internal Solenoid Valve Fault

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Symptoms: Dashboard ABS and brake system warning lights stay on. Scanner shows DTC C001104. ABS inoperative while driving but conventional braking works normally. Diagnostic process: Performed actuator test — left front outlet valve shows no response. Measured 12.4V between connector pins 25 and 38 (normal). 25A fuse checks good. Swapped ABS pump with unit from a known-good vehicle; the fault code transferred with the pump, confirming internal ABS pump solenoid valve failure. Solution: Replaced ABS hydraulic modulator assembly with ECU. Cleared codes and road tested (straight-line driving above 30 km/h for at least 10 seconds). Fault resolved; ABS warning light off.
Original source ↗
BYD DTC AI Analysis

BYD Song DM — Poor contact in ABS solenoid valve wiring

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Symptoms: ABS and brake system warning lights come on after starting. DTC C001104 sets intermittently and returns after clearing following a period of driving. The lights come on more easily on rough roads. Diagnosis: Found slight oxidation on pin 25 (solenoid valve power terminal) of the ABS hydraulic modulator connector; solenoid coil resistance measured normal; monitored pin voltage with a breakout box while driving and caught instantaneous drops over bumps (from 12V to below 8V); traced the harness and found a loose connection at the root of the ABS pump body connector. Solution: Cleaned and treated the oxidized pins on the ABS hydraulic modulator connector, re-secured and wrapped the wiring harness, reinforced the connector with a dedicated fixture, cleared the DTC and road-tested. Fault did not reappear.
BYD DTC AI Analysis

BYD e5 – ABS ECU control module fault

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Symptoms: Ignition switched to ON, abnormal clicking heard during ABS self-check. Instrument cluster displayed ABS fault. DTCs C001104 and C001004 (left front inlet valve fault) set simultaneously. Vehicle failed ABS self-check; system entered conventional braking mode. Diagnosis: Actuator test showed no feedback from either left front solenoid. Solenoid supply voltage measured 12V (normal), ground good. Continuity between solenoid drive terminals and ECU normal. Internal solenoid drive circuit in ABS ECU faulty; unable to drive left front solenoids. Solution: Replaced ABS hydraulic modulator assembly with integrated ECU. Bled brakes, initialized system, cleared DTCs. Performed dynamic test (checked wheel speed signals above 2 km/h). ABS function normal.
BYD DTC AI Analysis

BYD Tang - DTC triggered after brake system repair

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Symptoms: After brake fluid replacement and left front brake caliper repair, the ABS warning light came on. Fault codes: C001104 and C012104 (solenoid valve relay circuit fault). ABS was normal before this repair. Diagnosis: Checked repair history: recent brake system work. Found the ABS hydraulic modulator connector contaminated with brake fluid from installation. Measured solenoid valve supply voltage at 9.2V (below spec). The 25A fuse holder had burn marks and increased contact resistance. Brake fluid entered the connector during repair, causing the circuit fault. Resolution: Cleaned the ABS hydraulic modulator connector with electrical contact cleaner to remove brake fluid residue. Replaced the 25A fuse and fuse holder; supply voltage now above 12V. Bled the ABS system again and cleared fault codes. System returned to normal.
BYD DTC AI Analysis

BYD F3 - Wiring short circuit caused false solenoid valve fault

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Symptoms: ABS warning light came on suddenly while driving with abnormal braking feel (slight pedal vibration). DTC C001104 persisted and returned immediately after clearing. Inspection found chafing marks on the left front wheel speed sensor harness where it contacts the body. Diagnosis: Read DTC C001104 and initially suspected a left front outlet valve circuit fault. Checked ABS hydraulic modulator power and ground—both normal. While inspecting the left front wheel speed sensor circuit, found the harness insulation damaged with internal wires shorting to ground. Further inspection revealed signal interference between the wheel speed sensor circuit and solenoid valve control circuit, causing the ECU to misdiagnose a solenoid valve circuit fault; the solenoid valve itself was normal. Fix: Repaired the damaged section of the left front wheel speed sensor harness, rewrapped and insulated it, rerouted the harness to prevent chafing against the body or other components, cleared the code and confirmed the fix.
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.