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 — Atto 8

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.

5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1EPB actuator motor internal coil burnt out or open circuit: Prolonged motor operation causes overheating, the internal winding opens, and resistance becomes infinite (normal: 1.2-2.0Ω).
  • 2Wheel speed sensor signal interference: A loose right rear wheel speed sensor connector, damaged wiring harness, or iron filings on the magnetic encoder ring cause the EPB control unit to receive an unreliable wheel speed signal and incorrectly detect an actuator fault.
  • 3CAN communication circuit fault: Worn insulation on the CAN-H/CAN-L wiring harness between the EPB control unit and the vehicle network at the right rear quarter panel causes a short to ground or abnormal signal voltage (deviating from the 2.5V reference).
  • 4Control unit software bug: Specific software versions (e.g., 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 brake light switch contacts prevent the EPB control unit from receiving a valid "brake pedal 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 'loss of communication with EPB', and confirm the vehicle speed, temperature, and other environmental conditions at the time of the fault.
  • 2
    Raise the vehicle and inspect the right rear EPB actuator connector for broken locking tabs, 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 the connector for looseness, and clean iron filings from the magnetic encoder ring surface to eliminate false faults from signal interference.
  • 5
    Check the brake light switch: Verify synchronization of the two signal circuits on the four-wire switch, measure the output voltage (should be 12V/B+), and rule out burnt contacts causing signal inconsistency.
  • 6
    If the hardware check reveals no faults, 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 standard 6-8A 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 Atto 8 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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.