AU
C003B04

DTC C003B04 indicates the ABS control unit detects an electrical fault in the right rear wheel speed sensor signal circuit, including open circuit, short to ground, short to power, or abnormal signal — Atto 8

Braking System

DTC C003B04 indicates the ABS control unit detects an electrical fault in the right rear wheel speed sensor signal circuit, including open circuit, short to ground, short to power, or abnormal signal.

The wheel speed sensor (typically utilizing Hall effect or electromagnetic principles) serves as a key input component for the ABS/ESC system.

It converts wheel speed into electrical signals and transmits them to the control unit to calculate slip ratio, vehicle speed, and travel direction.

Triggering this DTC degrades or disables functions such as Anti-lock Braking System (ABS), Electronic Brakeforce Distribution (EBD), Electronic Stability Program (ESP), and Automatic Emergency Braking (AEB).

The instrument cluster illuminates the ABS/ESC warning lamp to alert the driver.

In models such as the BYD E5, the sensor typically integrates into the wheel hub assembly and connects to the ABS control unit via the floor wiring harness.

The wiring routes through wear-prone areas like the chassis side member, frequently developing hidden faults after long-term use.

3
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Wheel speed sensor damage: Internal Hall element failure, coil open circuit, or coil short circuit, preventing signal generation or causing signal distortion.
  • 2Harness wear or crushing: Long-term vibration and friction damage the harness insulation under the chassis and at the bottom of the frame rail, causing a short to ground or an intermittent open circuit.
  • 3Internal open circuit in the floor wiring harness: The internal copper conductor breaks but the insulation remains intact. Vehicle vibration causes poor contact, resulting in an intermittent fault.
  • 4Spare part model mismatch: The replacement wheel hub unit assembly or sensor model does not match the original factory specification (e.g., missing suffix letter), causing incompatible electrical parameters or signal characteristics.
  • 5Incorrect sensor installation gap or abnormal tone ring: The sensor-to-tone ring gap is too large or too small, or the tone ring is deformed, missing teeth, or contaminated, causing an implausible signal and triggering a circuit fault judgment.
What To Do
  • 1
    Use the VDS diagnostic tool to read the fault code and freeze frame data. Check the data stream for an abnormal right rear wheel speed signal (e.g., displaying an unreasonable value such as 2252km/h, or differing excessively from other wheel speeds).
  • 2
    Visual inspection: Check the right rear wheel speed sensor installation. Check the connector for looseness, water ingress, or oxidation. Measure the sensor supply voltage (Ignition ON: should be approximately 12V or 5V, depending on vehicle model).
  • 3
    Sensor component inspection: Measure the sensor resistance (standard value for a magnetic induction type is usually 1-1.5 kΩ) or check the signal output waveform (a Hall-effect type should output a square wave). Compare the readings with the left rear wheel to determine the sensor condition.
  • 4
    Circuit continuity check: Disconnect the ABS control unit and sensor connectors. Measure the harness resistance between them (should be less than 1Ω) and measure the insulation resistance to ground and power supply (should be greater than 10MΩ).
  • 5
    Dynamic wiring harness test: Wiggle and pull the sensor wiring harness (especially the floor harness section and the bottom of the chassis rail) while monitoring the scan tool data stream or measuring voltage changes to identify intermittent open circuits.
  • 6
    Reluctor ring inspection: Raise the vehicle and inspect the reluctor ring on the right rear half shaft or wheel hub for deformation, missing teeth, cracks, contamination (such as metal shavings or dirt), or demagnetization.
  • 7
    Spare part verification: If replacing, confirm the new part number exactly matches the original (note suffix differences, such as HAD-3630330 and HAD-3630330A). If necessary, swap the left and right sensors to cross-validate.
  • 8
    Repair verification: After rectifying the fault, clear the DTC and perform a road test (including flat and bumpy roads). Confirm the data stream is normal, the fault lamp is off, and system function returns to normal.
Real-World Cases
BYD DTC AI Analysis

Wiring harness chafed through to ground, causing ABS warning light to illuminate intermittently.

✓
BYD F3 with approximately 103,000 km. ABS warning light intermittently illuminated while driving. Live data showed right rear wheel speed at 2252 km/h (other wheels at 0). Replaced the sensor; no change. Measured wiring and found continuity to body. Found white-red wire chafed through at bottom of right side member. Taped and secured wiring. Fault cleared.
Original source ↗
BYD DTC AI Analysis

Internal break in floor wiring harness causes faults on bumpy roads

✓
When driving on rough roads, the dashboard displayed 'Automatic Emergency Braking function limited, please check ESP system'; flat roads normal. VDS scan showed C003B04 and other codes. Sensor voltage tested normal, but fluctuated abnormally when tugging the wiring harness. Diagnosed internal break in floor wiring harness. Replaced floor wiring harness assembly; fault resolved.
Original source ↗
BYD DTC AI Analysis

Replacement part number mismatch caused sensor failure

✓
ESP warning lamp on; VDS reported C003B04. Checked sensor power supply — normal. Replaced wheel hub unit assembly (including sensor); fault remained. Swapped left/right sensor harnesses; fault transferred, confirming the new part was defective. Found ordered PN was HAD-3630330, while the original vehicle had HAD-3630330A (A suffix). Installed the correct PN; fault cleared.
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.