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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.

5
Cases Logged
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.
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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
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.