AU
C003A08

C003A08 indicates the ABS control unit detects an abnormal right rear wheel speed sensor (RR WSS) signal — Atto 8

Braking System

C003A08 indicates the ABS control unit detects an abnormal right rear wheel speed sensor (RR WSS) signal.

Trigger conditions for this fault code include: complete loss of sensor signal (0 signal), signal amplitude below threshold, signal frequency mismatching the vehicle dynamics model (e.g., the other three wheels operate normally but the right rear signal changes abruptly), or electromagnetic interference causing signal noise.

In BYD ABS systems, subtype 08 specifically denotes a signal plausibility fault or intermittent signal interruption, distinct from an open circuit (C003B) or power supply fault.

This fault causes partial or complete failure of the ABS, EBD, ESC, TCS, and Automatic Emergency Braking (AEB) functions.

The vehicle enters limp braking mode, retaining only basic hydraulic braking.

The C003A08 fault code on the Atto 8 indicates an abnormal right rear wheel speed sensor signal, such as signal loss, weak output, mismatch, or interference. Severity is medium because ABS, EBD, ESC, TCS, and AEB may be partly or fully disabled, leaving basic braking only. Common causes include a failed wheel speed sensor or damaged/wet wiring connector. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Wheel speed sensor failure: Internal coil open/short circuit (magnetic induction type) or Hall element aging (Hall type). On E5 models, prolonged high temperatures near the exhaust pipe thermal management area accelerate aging of the right rear wheel sensor.
  • 2Wiring harness and connector fault: The right rear sensor wiring harness passes through the chassis side member mounting point. Vibration easily chafes the insulation, or an aging connector seal allows water ingress, causing an intermittent short circuit.
  • 3Abnormal sensor installation gap: Hub bearing wear causes the air gap between the sensor and tone ring to exceed tolerance (standard: 0.3-1.2 mm), or the sensor retaining bolt is loose.
  • 4Signal tone ring (magnetic ring) issue: Iron filings or mud attracted to the tone ring surface, or the tone ring is deformed, missing teeth, or demagnetized (integrated magnetic rings in certain BYD E5 bearing batches risk demagnetization).
  • 5ABS control unit signal processing circuit fault: Burnt internal sampling resistor or faulty ADC conversion module triggers a false sensor signal fault.
What To Do
  • 1
    Diagnostic confirmation: Use VDS3000 to read complete DTCs and freeze frame data. Confirm vehicle speed and wheel speed values at the time of the fault. Check for accompanying C003B00 (power supply fault) or U-class communication faults.
  • 2
    Visual inspection: Raise the vehicle and check the installation status of the right rear wheel speed sensor. Inspect the sensor tip for dirt, the wiring harness for wear, and the connector for looseness or water ingress. Check the inner side of the tyre for foreign metal objects.
  • 3
    Resistance measurement: Disconnect the sensor connector and measure the sensor resistance (magnetic induction standard value: 1.0-1.6 kΩ at 20°C). If the resistance is infinite or close to 0 Ω, replace the sensor. Measure the harness insulation resistance to ground; the value must exceed 10 MΩ.
  • 4
    Signal waveform check: Connect an oscilloscope and rotate the wheel. The magnetic type should output a sine wave (amplitude increases with wheel speed, typically 0.1V-5V). The Hall type should output a square wave. Check for waveform interruptions or noise.
  • 5
    Tone ring inspection: Remove the brake disc. Inspect the tone ring integrated on the wheel hub bearing for dirt or deformation. Clean the tone ring or replace the wheel hub bearing assembly (for BYD E5, replace the bearing with magnetic ring as a complete unit).
  • 6
    Air gap measurement: Use a feeler gauge to check the air gap between the sensor and tone ring. If bearing wear causes an excessive gap, replace the wheel hub bearing.
  • 7
    Road test verification: Clear the fault code, drive straight at above 20 km/h, and perform left and right turns. Verify in the ABS data stream that the right rear wheel speed synchronizes with the other wheel speeds, the fault light turns off, and the fault does not recur.
Real-World Cases
BYD DTC AI Analysis

E5 taxi right rear wheel speed sensor intermittent failure

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Vehicle: 2018 BYD E5 taxi, 280,000 km. Symptoms: ABS and ESP warning lights come on intermittently, especially on rough roads. Diagnosis: Scanned DTC C003A08 (intermittent). Freeze frame showed right rear wheel speed at 0 km/h while other wheels read 45 km/h when the fault occurred. Lifted the vehicle and found the right rear sensor wiring harness chafed through near the fuel line retaining clip, exposing copper wires. Road bumps caused the wires to short to ground against the body. Repair: Repaired the damaged harness section, reinforced insulation with heat-shrink tubing, and rerouted the wiring away from sharp edges. Fault resolved.
BYD DTC AI Analysis

BYD E5 right rear wheel hub bearing magnetic ring demagnetization

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Vehicle: 2019 BYD E5, 120,000 km. Symptoms: Dashboard displayed "Check ABS System", DTC C003A08 could not clear. Diagnosis: Sensor resistance measured 1.2kΩ (normal), 12V supply normal, but oscilloscope showed extremely low signal amplitude (peak only 0.05V). Removed sensor and found heavy iron powder buildup on the head; signal remained weak after cleaning. Further inspection revealed obvious wear marks on the wheel hub bearing's integrated magnetic ring with weakened magnetism. Fix: Replaced right rear wheel hub bearing assembly (including magnetic ring) and installed new sensor (replace both together). Fault resolved.
BYD DTC AI Analysis

Right rear wheel speed sensor signal interference after driving through water

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Vehicle: 2018 BYD E5, driven through heavy flood water. Symptoms: ABS warning light on steady, DTC C003A08. Diagnosis: Right rear wheel speed sensor connector showed visible water stains and white oxide on the pins. Sensor body resistance checked normal, but signal wire-to-ground insulation measured only 0.5MΩ (spec >10MΩ). Water entered the connector during wading, causing slight leakage to ground on the signal line. The resulting electrical noise made the ABS ECU interpret the signal as abnormal. Repair: Thoroughly cleaned the connector pins, blew out the moisture, applied conductive anti-corrosion compound, and wrapped the connector with waterproof tape. Fault cleared.
BYD DTC AI Analysis

Aftermarket wheels caused abnormal sensor gap

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Vehicle: 2019 BYD E5, aftermarket 17-inch wheels fitted. Symptom: ABS light flashes intermittently while driving. DTC: C003A08. Diagnosis: The aftermarket wheels’ center bore is slightly off from OEM spec, causing the wheels to sit further outboard. This increases the sensor-to-tone-ring air gap to 2.1 mm (out of specification). Signal is adequate at low speed but amplitude drops too low at high speed, causing the ECU to set the fault code. Solution: Reverted to OEM-spec wheels (or fitted hub centric rings to correct positioning) and adjusted sensor mounting. Fault cleared.
BYD DTC AI Analysis

Misdiagnosed as ABS control unit internal circuit fault

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Vehicle: 2018 BYD E5. Multiple repairs failed to resolve the issue. Symptoms: DTC C003A08 kept returning. Replaced sensor, harness and wheel bearing; fault persisted. Diagnosis: Cross-connected right rear sensor harness to left rear channel (modified harness connector). Left rear wheel speed signal read normally, yet ABS ECU still set C003A08 (right rear fault) despite the physical connection being the left rear sensor. Isolated the fault to internal signal processing circuit in ABS control unit's right rear channel. Repair: Replaced ABS pump assembly (including ECU). Bled brakes and performed programming/calibration. Fault completely resolved.
Other Atto 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.