UAE
AU
C002004

DTC C002004 indicates a functional fault in the return pump motor inside the ABS/ESC Hydraulic Control Unit (HCU) — Atto 3

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
Real-World Cases
BYD DTC AI Analysis

2014 BYD Qin Hybrid: Oxidized ABS connector causing DTC C002004

✓
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.

✓
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

✓
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

✓
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

✓
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 Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
Data confidence: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.