AU
C004C04

On BYD new energy vehicles (particularly the E5 and Song series), DTC C004C04 indicates a circuit fault in the Electronic Parking Brake (EPB) right rear wheel actuator, rather than an ESP switch fault as stated in the original documentation — Seal 6 EV

Braking System

On BYD new energy vehicles (particularly the E5 and Song series), DTC C004C04 indicates a circuit fault in the Electronic Parking Brake (EPB) right rear wheel actuator, rather than an ESP switch fault as stated in the original documentation.

Specifically, the EPB control unit detects an open circuit, short circuit, or abnormal resistance in the right rear parking motor circuit, preventing the motor from completing the clamp/release action.

This fault triggers the system protection mechanism.

It may cause the right rear wheel to lock mechanically, prevent the EPB from releasing automatically (failing to disengage when shifting into gear and applying the accelerator), and compromise vehicle launch and driving safety.

Although the EPB and ESP (Electronic Stability Program) interact during brake management, this code specifically indicates a hardware or wiring fault in the parking brake actuator.

The C004C04 fault code on the Seal 6 EV indicates a medium-severity circuit fault in the right rear Electronic Parking Brake actuator. The parking brake motor may not clamp or release correctly, which can affect vehicle launch and safety. Common causes include a failed EPB actuator motor or interference from the right rear wheel speed sensor wiring. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1EPB actuator motor internal coil burned out or open circuit: Prolonged motor operation causes overheating, opening the internal winding and resulting in infinite resistance (normal: 1.2-2.0Ω).
  • 2Wheel speed sensor signal interference: A loose right rear wheel speed sensor connector, damaged wiring harness, or iron filings attached to the magnetic encoder ring cause the EPB control unit to receive an unreliable wheel speed signal and incorrectly diagnose an actuator fault.
  • 3CAN communication circuit fault: The CAN-H/CAN-L wiring harness between the EPB control unit and the vehicle network chafes at the right rear quarter panel, causing a short to ground or abnormal signal voltage (deviating from the 2.5V reference).
  • 4Control unit software bug: Specific software versions (such as V2.1.2 and earlier) set the motor resistance detection threshold too strictly in low-temperature conditions, triggering false faults during cold starts.
  • 5Brake light switch signal abnormal: Burnt internal contacts in the brake light switch prevent the EPB control unit from receiving a valid "brake applied" signal, triggering circuit fault protection.
What To Do
  • 1
    Use the BYD VDS diagnostic tool to read the complete EPB system fault codes and freeze frame data. Check for accompanying network fault codes, such as 'Lost communication with EPB', and confirm environmental conditions at the time of the fault, including vehicle speed and temperature.
  • 2
    Raise the vehicle. Check the right rear EPB actuator connector for broken locking clips, backed-out terminals, water ingress, or oxidation. Measure the motor resistance. Standard: 1.2-2.0 Ω. Infinite resistance indicates an internal motor open circuit.
  • 3
    Measure the EPB control unit power supply (constant B+ 12V), ignition switch power supply, and ground circuit; measure the CAN line voltage (CAN-H 2.5-2.7V, CAN-L 2.3-2.5V), and inspect the wiring for short or open circuits.
  • 4
    Check the right rear wheel speed sensor: measure the resistance (1.5-2.0kΩ), check for a loose connector, clean iron filings from the magnetic encoder ring surface, and eliminate false faults caused by signal interference.
  • 5
    Check the brake light switch: verify synchronization of the two signal circuits in the four-wire switch, measure the voltage output (should be 12V/B+), and rule out burnt contacts as the cause of signal inconsistency.
  • 6
    If the hardware inspection reveals no abnormalities, consult the Technical Service Bulletin (TSB) to confirm the software version. Use VDS to update the EPB control unit to the latest version (e.g., V2.3.5+) to optimize the low-temperature detection algorithm.
  • 7
    After replacing the faulty component (EPB actuator assembly, wiring harness connector, or brake light switch), perform the EPB initialization learning procedure: calibrate the cable travel using the diagnostic tool, perform multiple clamp/release cycle tests, and confirm the current is within the 6-8A standard range.
Real-World Cases
BYD DTC AI Analysis

BYD Qin Pro DM – Right rear EPB motor internal open circuit

✓
After parking, the electronic handbrake would not release and the instrument panel displayed "Check Electronic Parking System". The right rear wheel locked up. Used VDS to read DTC C004C04 (right rear EPB motor circuit open). Measured resistance at the right rear EPB actuator motor plug and found infinite resistance, indicating the internal coil had burnt out. Replaced the right rear electronic parking brake actuator assembly (P/N 10237938-00). Performed EPB initialization learning and cleared the fault.
Original source ↗
BYD DTC AI Analysis

BYD Song PLUS DM-i - Wheel speed sensor signal interference causing false fault codes

✓
While driving, the ESP light suddenly came on and the electronic handbrake indicator flashed. The warning disappeared after stopping and restarting. Read DTC C004C04 (right rear wheel speed sensor signal unreliable). Found the right rear wheel speed sensor connector locking clip broken and loose, and the hub bearing magnetic encoder ring covered with iron debris. Cleaned the encoder ring and sensor probe, replaced the connector and secured the wiring harness. Fault has not recurred.
Original source ↗
BYD DTC AI Analysis

BYD Tang DM (Second Generation) - Damaged CAN wiring harness

✓
Vehicle failed to start. Dashboard displayed 'Check Electronic Parking Brake System' and 'Check ESP System'. Unable to select gears. Scan revealed EPB DTC C004C04 (communication timeout) and ABS/ESP loss of communication with EPB. Measured abnormal CAN bus voltages: CAN-H 2.8V, CAN-L 2.2V. Removing the right rear interior trim panel revealed the wiring harness had chafed through and shorted at a sheet metal hole. Repaired the damaged CAN wiring, insulated and waterproofed the repair, and rerouted the harness. Vehicle returned to normal.
Original source ↗
BYD DTC AI Analysis

BYD Han EV - Control unit software bug

✓
When cold-starting the vehicle in winter, the dashboard displayed 'Electronic Parking System Fault'. The warning cleared after 3-5 minutes and did not return when the vehicle was warm. Read historical DTC C004C04; no current faults present. Hardware inspection found no issues. Checked the TSB and confirmed software version V2.1.0 had an overly strict low-temperature detection threshold. Upgraded the EPB control unit software to V2.3.5, optimizing the low-temperature detection algorithm. Continuous testing confirmed the fault was resolved.
Original source ↗
BYD DTC AI Analysis

BYD e5 450 - Brake Light Switch Fault

✓
Electronic parking brake won't auto-release (doesn't disengage when selecting Drive and applying throttle), cruise control inoperative. EPB system stored DTC C004C04 (brake signal validation failure); motor control system simultaneously logged 'brake switch signal inconsistency'. Checked the brake light switch: one signal circuit measured only 3.2V (should be 12V), confirming internal contact burn-out. Replaced brake light switch assembly (HA2-3720010) and adjusted mounting clearance to 1.5-2.0mm. Fault resolved.
Original source ↗
Other Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV 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.