AU
C001C04

DTC C001C04 indicates an electrical or mechanical fault in the right rear wheel inlet valve within the ABS/ESC Hydraulic Control Unit (HCU) — Atto 8

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).

The C001C04 fault code on the Atto 8 indicates a medium-severity fault with the right rear wheel inlet valve in the ABS/ESC Hydraulic Control Unit. It may be caused by an open or short circuit in the solenoid coil, abnormal resistance, corroded connector pins, or damaged wiring. ABS, EBD, ESC, and AEB operation may be limited. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Open circuit or abnormal resistance in the right rear inlet valve solenoid coil within the hydraulic modulator assembly (normal resistance is typically 2-5Ω; out of tolerance).
  • 2Poor contact at the wiring harness connector between the ABS ECU and hydraulic modulator, corroded pins, or damaged wiring harness, interrupting drive signal transmission.
  • 3ABS ECU internal valve drive circuit fault (e.g., damaged power MOSFET, driver chip, or sampling resistor) resulting in insufficient drive current (typically requires 1-2A peak current)
  • 4Severely contaminated brake fluid (containing metal debris, moisture, or degraded fluid) causes the inlet valve spool to stick in the open or closed position. The ECU detects the anomaly via current feedback.
  • 5Previous vehicle wading or accident caused moisture, oxidation, or physical damage to the hydraulic modulator internal circuit board, affecting solenoid valve control.
What To Do
  • 1
    Use a dedicated diagnostic tool (such as BYD VDS or Launch X431) to read all fault codes and freeze frame data. Confirm if C001C04 is a current fault. Check for accompanying faults such as C001C00 (right rear inlet valve drive fault) or other wheel speed sensor faults. Clear the fault codes and perform a road test to observe if the fault returns.
  • 2
    Inspect the appearance of the ABS hydraulic modulator and wiring harness connector: check the hydraulic modulator assembly plug near the right rear wheel for looseness, water ingress, oxidation, or burn damage. Measure the wiring harness continuity (must be less than 1Ω) and insulation resistance (must be greater than 10MΩ to prevent a short to ground or power) between the ABS ECU and the corresponding hydraulic modulator pins.
  • 3
    Solenoid valve resistance measurement: Disconnect the hydraulic modulator connector. Use a multimeter to measure the right rear inlet valve coil resistance (refer to the wiring diagram for pin locations, typically the corresponding RL inlet valve pin inside the HCU). The normal value is 2.0-5.0 Ω (refer to the E5 workshop manual for exact standard values). If the resistance is infinite (open circuit) or near 0 (short circuit), this indicates an internal fault in the hydraulic modulator assembly.
  • 4
    Actuator operation test: Connect the diagnostic tool and enter the ABS active test function. Perform the 'right rear inlet valve' actuation test. Use a stethoscope or touch the valve body to detect a clear 'click' switching sound. If no sound occurs but the ECU reports a drive fault, use the resistance measurement results to confirm a valve body or circuit fault.
  • 5
    Replacement and verification: If diagnostics confirm a hydraulic modulator assembly fault (the BYD E5 ABS ECU and HCU feature an integrated design; do not replace the solenoid valve separately), replace the complete ABS hydraulic modulator assembly. After replacement, perform: ① brake system bleeding procedure (use a diagnostic tool to bleed the pump motor); ② longitudinal acceleration sensor and yaw rate sensor calibration; ③ wheel speed sensor signal check; ④ road test to verify ABS/ESC function and DTC status.
Real-World Cases
BYD DTC AI Analysis

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

✓
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.

✓
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.

✓
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.

✓
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 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.