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C001C04

DTC C001C04 indicates an electrical or mechanical fault in the right rear wheel inlet valve within the ABS/ESC Hydraulic Control Unit (HCU) — Seal U

Braking System

DTC C001C04 indicates an electrical or mechanical fault in the right rear wheel inlet valve within the ABS/ESC Hydraulic Control Unit (HCU).

The right rear inlet valve is a normally open high-speed solenoid valve controlling the hydraulic passage from the brake master cylinder to the right rear wheel brake cylinder.

This fault indicates the ABS ECU detects an open circuit or short circuit (to power or ground) in the right rear inlet valve drive circuit, a stuck valve spool, or an abnormal response.

This prevents the ECU from accurately regulating brake pressure at the right rear wheel.

This directly affects the execution of Anti-lock Braking System (ABS), Electronic Brakeforce Distribution (EBD), Electronic Stability Control (ESC), and Automatic Emergency Braking (AEB) functions at the right rear wheel.

In extreme cases, this causes right rear wheel braking failure or lock-up, triggers multiple system warnings, and initiates fail-safe mode (conventional hydraulic braking remains operational, but electronic assist functions are limited).

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Cases Logged
Real-World Cases
BYD DTC AI Analysis

Replaced HCU assembly on BYD E5 taxi due to open circuit in right rear inlet valve coil

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A 2018 BYD E5 taxi with 280,000 km showed illuminated ABS and ESC warning lights. Scanning revealed DTCs C001C04 (right rear inlet valve fault) and C001D00 (right rear outlet valve fault). Technicians measured the hydraulic modulator connector and found infinite resistance (open circuit) between the right rear inlet valve pins; other wheel valves showed normal resistance of approximately 3.2 Ω. Disassembling the ABS assembly revealed fatigue cracks in the circuit board solder joints from long-term vibration. They replaced the ABS hydraulic modulator assembly (with ECU), clearing the fault. The assembly was out of warranty and classified as a wear item, so the owner paid for the replacement.
BYD DTC AI Analysis

Water ingress caused connector corrosion, triggering intermittent C001C04 fault.

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2019 E5 owner reported the ABS warning light intermittently illuminating after driving in wet conditions. DTC C001C04 stored as a historical fault. Inspection found green copper corrosion inside the 24-pin wiring harness connector for the ABS hydraulic modulator located near the right front wheel arch. The right rear inlet valve drive pin (typically pin X; refer to wiring diagram) showed slight oxidation, increasing contact resistance to 12Ω (normal: <0.5Ω). Cleaned the connector with precision electrical contact cleaner, applied conductive protective grease, and retightened. No recurrence after one month of monitoring.
BYD DTC AI Analysis

Brake fluid contamination jammed the valve spool and caused false alarms.

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An accident-repaired E5 developed a C001C04 fault after the workshop replaced the right rear brake caliper without thoroughly bleeding the system, then incorrectly added inferior brake fluid mixed with the original DOT4. Scanner showed the inlet valve circuit normal at 3.5Ω, but the valve made no sound during active testing. Disassembling the hydraulic modulator revealed the inlet valve spool jammed with gummy contaminants. Dedicated brake cleaning equipment failed to clear the blockage. The workshop replaced the hydraulic modulator assembly, flushed all brake lines, and replaced all brake fluid. Advised owner to replace brake fluid every 40,000 km or 2 years.
BYD DTC AI Analysis

Internal driver chip failure in the ABS ECU caused multiple valve faults.

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A 2018 BYD E5 triggered simultaneous DTCs C001C04 (rear right inlet valve) and C001B04 (rear left inlet valve). Resistance measured 3.0Ω and 3.1Ω at the two valves respectively, with harness continuity normal. Neither valve operated during individual actuation tests, indicating an internal ABS ECU driver circuit fault—likely a failed common ground driver chip. The BYD E5 uses an integrated ABS ECU/HCU design; repairing the ECU separately posed sealing risks. Replaced the complete ABS hydraulic modulator assembly, clearing the fault. Programmed and matched the replacement unit; vehicle returned to normal.
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.