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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 — Qin Plus

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 Qin Plus 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 actuator motor coil or interference from a loose/damaged right rear wheel speed sensor circuit. Have the vehicle inspected by an authorised dealer. Typical repair cost data is available from recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 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 on the magnetic encoder ring causes the EPB control unit to receive an unreliable wheel speed signal and falsely detect an actuator fault.
  • 3CAN communication circuit fault: Chafed CAN-H/CAN-L wiring harness between the EPB control unit and 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 (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'. Confirm the environmental conditions at the time of the fault, including vehicle speed and temperature.
  • 2
    Raise the vehicle and check the right rear EPB actuator connector for a broken locking clip, backed-out terminals, water ingress, or oxidation. Measure the motor resistance: standard is 1.2-2.0 Ω. An infinite reading 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 check the wiring for short or open circuits.
  • 4
    Check the right rear wheel speed sensor: measure resistance (1.5-2.0kΩ), inspect the connector for looseness, clean iron filings from the magnetic encoder ring surface, and eliminate false alarms caused by signal interference.
  • 5
    Check the brake light switch: verify synchronization between the two signal circuits of the four-wire switch, measure the output voltage (should be 12V/B+), and rule out burnt contacts causing inconsistent signals.
  • 6
    If the hardware inspection reveals no faults, check the Technical Service Bulletin (TSB) to confirm the software version. Use the 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 verify 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 Qin Plus 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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.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 Qin Plus →Qin Plus 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.