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 — Atto 8

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 Atto 8 indicates a circuit or functional fault in the left front ABS outlet valve inside the HECU. Severity is medium because ABS pressure reduction for that wheel may be disabled, increasing lock-up or pulling risk during hard braking. Common causes include a faulty solenoid valve or poor ABS pump connector/wiring connection. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available for this fault.
5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Open circuit or short circuit in the solenoid coil, or stuck valve spool in the internal left front outlet valve of the ABS hydraulic modulator assembly (internal mechanical fault)
  • 2Oxidized, loose, or backed-out ABS pump connector pins, 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), unable to output approximately 12V drive current to the solenoid valve.
  • 4Solenoid valve power supply circuit fault, including 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 related 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 and confirm C001104 is present. Check the freeze frame data to verify the vehicle speed and system status when the fault occurred.
  • 2
    Run the ABS system 'Actuator Test', select the left front outlet valve (LF Outlet Valve), and listen for a clear 'click' sound 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. Check pin 25 (solenoid valve power supply) and pin 38 (ground) for oxidation, burning, or brake fluid contamination.
  • 4
    Measure the solenoid valve supply voltage: Turn the ignition switch to ON. Use a multimeter to measure the voltage from connector pin 25 to ground. The standard value is 10-16V. Also check the 25A ABS fuse and its holder 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 5-10Ω (refer to the vehicle repair manual for exact specifications). Infinite resistance indicates an open circuit in the coil; 0Ω indicates a short circuit in the coil.
  • 6
    Check circuit continuity: 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, diagnose an internal fault in the ABS pump assembly (solenoid valve or ECU drive circuit). Replace the ABS hydraulic modulator assembly with the ECU (Note: Do not replace the solenoid valve separately).
  • 8
    After replacement, perform the brake system bleeding procedure (use the diagnostic tool to execute 'Bleeding Mode' to activate the oil pump). Clear the fault codes and perform a road test (exceed 30 km/h and maintain this speed for over 10 seconds to trigger the ABS self-check). Verify 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 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.