AU
C003A08

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

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.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Wheel speed sensor failure: Internal coil open/short circuit (magnetic induction type) or Hall element aging (Hall type). On E5 models, prolonged high temperatures from the adjacent exhaust pipe thermal management area accelerate right rear wheel sensor aging.
  • 2Wiring harness and connector fault: The right rear sensor wiring harness passes through the chassis side member mounting point, where vibration easily chafes the insulation, or an aging connector seal allows water ingress, causing an intermittent short circuit.
  • 3Abnormal sensor installation gap: Wheel hub bearing wear causes the air gap between the sensor and tone ring to be out of tolerance (standard: 0.3-1.2 mm), or the sensor retaining bolt is loose.
  • 4Signal tone wheel (magnetic ring) issue: Iron filings or mud adhering to the tone wheel surface, tone wheel deformation, missing teeth, or loss of magnetism (certain batches of BYD E5 bearings with integrated magnetic rings risk demagnetization).
  • 5ABS control unit signal processing circuit fault: burnt internal sampling resistor or faulty ADC conversion module causes false sensor signal faults.
What To Do
  • 1
    Diagnostic confirmation: Use VDS3000 to read all DTCs and freeze frame data. Confirm vehicle speed and wheel speed values when the fault occurred. Check for accompanying C003B00 (power supply fault) or U-class communication faults.
  • 2
    Visual inspection: Raise the vehicle and check the right rear wheel speed sensor installation. Inspect the sensor head for dirt, the wiring harness for wear, and the connector for looseness or water ingress. Check the inner side of the tyre for metallic foreign objects.
  • 3
    Resistance measurement: Disconnect the sensor connector and measure the sensor resistance (magnetic induction type 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; it must be greater than 10 MΩ.
  • 4
    Signal waveform check: Connect an oscilloscope and rotate the wheel. Magnetic inductive sensors should output a sine wave (amplitude increases with wheel speed, typically 0.1V-5V). Hall-effect sensors should output a square wave. Check for waveform interruptions or noise.
  • 5
    Tone ring inspection: Remove the brake disc. Check the tone ring integrated into 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 the 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 over 20 km/h and perform left and right turns. Verify the right rear wheel speed in the ABS data stream synchronizes with the other wheel speeds, the warning 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 Seal U 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.