AU
C002004

DTC C002004 indicates a functional fault in the return pump motor inside the ABS/ESC Hydraulic Control Unit (HCU) — Seal 6 EV

Braking System

DTC C002004 indicates a functional fault in the return pump motor inside the ABS/ESC Hydraulic Control Unit (HCU).

The return pump is a core actuator in the ABS system.

During the anti-lock braking cycle, it pumps brake fluid from the low-pressure side of the wheel cylinder back to the high-pressure side or the reservoir.

The fault falls into two categories: 1) "Unable to run" — Indicates an open or shorted motor winding, completely worn carbon brushes, a burnt commutator, or a damaged motor drive circuit (H-bridge MOSFET or relay) inside the ABS control module, preventing the pump motor from receiving drive current. 2) "Unable to stop running" — Indicates stuck motor drive relay contacts, failed control chip logic, or an abnormal feedback signal, causing the pump motor to run continuously when not required.

This fault directly disables ABS, ESP, and TCS functions.

In extreme cases, it affects brake pedal feel (hardening or abnormal pulsation).

This is a Level 2 fault affecting driving safety.

5
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Recirculation pump motor damage: Excessive motor carbon brush wear causing poor contact, a burnt commutator, or an open or shorted armature winding causes the motor to fail to start or operate weakly.
  • 2ABS control module drive circuit fault: The motor driver chip (H-bridge circuit), power MOSFET, or relay contacts inside the control module are burnt out or stuck, preventing the module from driving the motor or cutting off the motor power supply.
  • 3Power supply and wiring issues: Blown ABS hydraulic unit high-current fuse (usually 30A-60A), loose or oxidized power wiring connections, or poor ground connections, causing insufficient motor supply voltage or abnormal control signals.
  • 4Mechanical binding: Overdue brake fluid replacement causes the internal valve body or pump mechanism to bind. This generates excessive stall current at motor startup, triggering overcurrent protection or burning out the drive circuit.
  • 5Control module connector fault: Water ingress, oxidation, terminal back-out, or poor contact in the multi-pin connector between the ABS control module and the hydraulic unit interrupts or disrupts motor drive signal transmission.
What To Do
  • 1
    Fault confirmation and freeze frame recording: Use a dedicated BYD diagnostic tool (VDS2000/VDS6000 or Launch X431) to read fault code C002004. Record freeze frame data (vehicle speed, voltage, temperature, etc.) and confirm whether the fault is intermittent or continuous.
  • 2
    Basic circuit check: Check if the ABS pump high-current fuse in the engine compartment fuse box (marked ABS MOTOR or similar, usually 40A-60A) is blown; check the power supply (BAT+), ignition power (IG+), and ground (GND) voltages at the ABS control module connector, and verify the battery voltage is normal (above 12.6V).
  • 3
    Actuator test: Use the diagnostic tool to perform the 'Return Pump Active Test' and listen for the motor running inside the hydraulic unit. If there is no sound, measure the motor resistance. If the motor runs continuously and fails to stop, diagnose a stuck drive circuit.
  • 4
    Physical connection check: Disconnect the ABS control module connector and inspect the terminals for green oxidation, backed-out pins, enlarged pin holes, or signs of water ingress. Clean the connector with electrical contact cleaner, apply conductive grease, and reconnect it. Clear the fault code and road test the vehicle to confirm if poor contact caused the intermittent fault.
  • 5
    Motor resistance measurement (qualified personnel only): If certified for ABS repair, disassemble the hydraulic control unit and use a multimeter to measure the resistance between the two terminals of the return pump motor. Normal resistance is 2-5Ω (varies slightly by model). Infinite resistance (open circuit) or resistance near 0Ω (short circuit) confirms the motor itself is damaged.
  • 6
    Assembly Replacement and Matching: If diagnostics confirm an internal fault in the hydraulic unit, replace the ABS hydraulic control unit assembly (Note: BYD models usually require replacing the complete assembly; match the part number to the VIN). After installation, use a diagnostic tool to perform: ① Brake system bleeding procedure (sequence: right-rear - left-rear - right-front - left-front) ② ESC system calibration/configuration ③ Wheel speed sensor signal check
  • 7
    Function verification: Clear all fault codes and perform a road test: ① Brake hard at low speed (below 30 km/h) and confirm normal ABS operation with brake pedal pulsation; ② Drive in an S-pattern at medium to high speed (above 60 km/h) and confirm normal ESP intervention; ③ Verify the instrument cluster ABS/ESP warning lights are off and fault code C002004 does not reappear.
Real-World Cases
BYD DTC AI Analysis

2014 BYD Qin Hybrid: Oxidized ABS connector causing DTC C002004

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Vehicle: 2014 BYD Qin (petrol-electric hybrid). Symptoms: ABS and ESP warning lights stayed on. Scanner read fault code C002004 (return pump error). Repair: Checked ABS fuse — normal. Ran return pump actuator test; no response. Pulled ABS control module connector and found green oxide inside (likely from washing or wading). Several pins were corroded. Cleaned connector pins with electronic contact cleaner, applied conductive grease, and reconnected. Cleared codes and test drove — fault cleared temporarily. Two days later, fault returned. Inspection showed the return pump motor inside the hydraulic unit had overheated and failed from the prolonged poor contact. Final repair: Replaced ABS hydraulic control unit assembly. Performed brake bleed and ESC calibration after installation. Fault completely resolved.
Original source ↗
BYD DTC AI Analysis

BYD Song DM ABS return pump motor burned out, assembly replaced.

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Vehicle: 2017 BYD Song DM (plug-in hybrid). Symptoms: ABS, ESP and TCS warning lights illuminated suddenly while driving. Fault code: C002004. No ABS kickback felt during emergency braking; brake pedal stiff. Repair: Scan tool confirmed C002004; code would not clear. ABS pump supply voltage: 12.4 V (normal). Connector condition good. Return pump active test: relay clicked but motor did not run. Diagnosed as motor body or drive circuit fault. The BYD Song DM uses an integrated ABS/ESC assembly (Bosch or Continental system); the return pump motor and ECU are inside the hydraulic unit and cannot be replaced separately. Replaced ABS hydraulic control unit assembly (PN 5A-XXXXXX). Used Launch X431 to bleed brake system and configure ESC. Road test: ABS function normal.
Original source ↗
BYD DTC AI Analysis

BYD F3: Return pump relay stuck, causing continuous pump operation

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Vehicle: 2015 BYD F3 (Bosch 8.1 ABS). Symptoms: ABS pump runs continuously with a buzzing noise after the ignition is switched on, keeps running briefly after the ignition is switched off, and the ABS warning light stays on. Fault code: C002004 (Unable to Stop Running). Repair: This fault manifests as "unable to stop running" — the opposite of the common "unable to run" failure. Inspection of the ABS control module revealed the return pump relay contacts had fused together, keeping the pump motor powered continuously. The F3 ABS assembly is interchangeable with certain Volkswagen models and readily available on the used market. The owner chose a salvaged ABS assembly (cost: approximately 400 yuan). Replacement cleared the fault — the ABS warning light went out and the pump now operates normally (running only during ABS activation or self-check).
Original source ↗
BYD DTC AI Analysis

Sticking return pump on BYD e5 commercial vehicle caused regenerative braking failure

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Vehicle: 2018 BYD e5 (battery electric taxi, 180,000 km). Symptoms: Dashboard displayed "Check Braking System" and "Check ESP", DTC C002004, regenerative braking completely inoperative, significant range loss. Diagnosis: The e5 uses an Electro-Hydraulic Brake (EHB) system; the ABS return pump modulates hydraulic pressure for regenerative braking. The scan tool read C002004; the pump motor showed no response during the actuator test. Disassembled the ABS hydraulic unit and found the return pump motor carbon brushes completely worn from prolonged high-load operation (frequent taxi braking). The brake fluid had not been changed for over 50,000 km, causing poor lubrication and mechanical seizure inside the pump. Fix: Replaced the ABS hydraulic control unit assembly, replaced the brake fluid (DOT4), and calibrated the ESC system. Result: Regenerative braking restored, fault codes cleared.
Original source ↗
BYD DTC AI Analysis

BYD Qin Pro EV ABS Control Module Circuit Board Repair Case

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Vehicle: 2019 BYD Qin Pro EV (battery electric). Symptoms: ABS and ESP warning lights on. Scan tool showed DTC C002004 (return pump error). ABS pump self-test noise at startup, but ABS inoperative while driving. Repair: Checked ABS power and ground — normal. No connector oxidation. Oscilloscope check revealed no PWM drive signal from control module to return pump. Internal motor driver chip (H-bridge) faulty. Dealership quoted ~¥3,200 for complete ABS assembly replacement; owner chose professional electronics repair. Disassembled ABS control module (ECU separated from hydraulic unit), replaced internal motor driver chip (MOSFET), resealed and reinstalled. Cleared DTCs and performed brake bleed. Road test confirmed fault resolved; ABS function restored.
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.